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The present study examined the impact of breakfast and exercise on postprandial metabolism, appetite and macronutrient balance. A sample of twelve (blood variables n 11) physically active males completed four trials in a randomised, crossover design comprising a continued overnight fast followed by: (1) rest without breakfast (FR); (2) exercise without breakfast (FE); (3) breakfast consumption (1859 kJ) followed by rest (BR); (4) breakfast consumption followed by exercise (BE). Exercise was continuous, moderate-intensity running (expending approximately 2·9 MJ of energy). The equivalent time was spent sitting during resting trials. A test drink (1500 kJ) was ingested on all trials followed 90 min later by an ad libitum lunch. The difference between the BR and FR trials in blood glucose time-averaged AUC following test drink consumption approached significance (BR: 4·33 (sem 0·14) v. FR: 4·75 (sem 0·16) mmol/l; P= 0·08); but it was not different between FR and FE (FE: 4·77 (sem 0·14) mmol/l; P= 0·65); and was greater in BE (BE: 4·97 (sem 0·13) mmol/l) v. BR (P= 0·012). Appetite following the test drink was reduced in BR v. FR (P= 0·006) and in BE v. FE (P= 0·029). Following lunch, the most positive energy balance was observed in BR and least positive in FE. Regardless of breakfast, acute exercise produced a less positive energy balance following ad libitum lunch consumption. Energy and fat balance is further reduced with breakfast omission. Breakfast improved the overall appetite responses to foods consumed later in the day, but abrogated the appetite-suppressive effect of exercise.
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Breakfast and exercise contingently affect postprandial metabolism and
energy balance in physically active males
Javier T. Gonzalez
1
*, Rachel C. Veasey
1
, Penny L. S. Rumbold
2
and Emma J. Stevenson
1
1
Brain, Performance and Nutrition Research Centre, School of Life Sciences, Northumbria University, Northumberland
Building, Newcastle upon Tyne NE1 8ST, UK
2
Department of Sport and Exercise Sciences, School of Life Sciences, Northumbria University, Northumberland Building,
Newcastle upon Tyne NE1 8ST, UK
(Submitted 30 July 2012 – Final revision received 4 October 2012 – Accepted 14 November 2012)
Abstract
The present study examined the impact of breakfast and exercise on postprandial metabolism, appetite and macronutrient balance.
A sample of twelve (blood variables n11) physically active males completed four trials in a randomised, crossover design comprising a
continued overnight fast followed by: (1) rest without breakfast (FR); (2) exercise without breakfast (FE); (3) breakfast consumption
(1859 kJ) followed by rest (BR); (4) breakfast consumption followed by exercise (BE). Exercise was continuous, moderate-intensity running
(expending approximately 2·9 MJ of energy). The equivalent time was spent sitting during resting trials. A test drink (1500 kJ) was ingested
on all trials followed 90 min later by an ad libitum lunch. The difference between the BR and FR trials in blood glucose time-averaged
AUC following test drink consumption approached significance (BR: 4·33 (SEM 0·14) v. FR: 4·75 (SEM 0·16) mmol/l; P¼0·08); but it
was not different between FR and FE (FE: 4·77 (SEM 0·14) mmol/l; P¼0·65); and was greater in BE (BE: 4·97 (SEM 0·13) mmol/l) v.BR
(P¼0·012). Appetite following the test drink was reduced in BR v.FR(P¼0·006) and in BE v.FE(P¼0·029). Following lunch, the most
positive energy balance was observed in BR and least positive in FE. Regardless of breakfast, acute exercise produced a less positive
energy balance following ad libitum lunch consumption. Energy and fat balance is further reduced with breakfast omission. Breakfast
improved the overall appetite responses to foods consumed later in the day, but abrogated the appetite-suppressive effect of exercise.
Key words: Appetite: Fasted state: Glycaemia: Fat oxidation
Regular breakfast consumption has been inversely associated
with BMI
(1)
, yet it is not clear whether this association is due
to differences in energy expenditure, metabolism or energy
intake. Although the ostensible benefits of regular breakfast
consumption could be due to improved diet composition
with breakfast cereals
(1)
, rather than meal pattern per se,
acute consumption of breakfast can enhance glucose
tolerance, insulin sensitivity and subjective and physiological
satiety responses to a test drink
(2)
.
A recent position statement concluded that further research
is required in regular exercisers with regards to meal pattern,
metabolism and appetite regulation
(3)
, as research in exercis-
ing individuals in this area is sparse. However, this population
do use diet/exercise strategies, such as training in the fasted
state, to control body fat/mass and improve metabolic
adaptations to training
(4)
. Exercise attenuates adverse dietary
outcomes such as fat-induced glucose intolerance
(5)
, and the
nutritional state in which exercise is performed can modulate
the magnitude of these improvements
(5)
. Exercise in the fasted
state results in a greater reliance on fat as a substrate
(6)
and
has led to its use as a tool to reduce body fat by athletes
(4)
.
Training in the fasted state also leads to enhanced fat transpor-
ter protein mRNA content
(5)
, mitochondrial enzyme activity
and maximal aerobic capacity
(7)
, making exercise in the
fasted state an attractive proposition for both recreational
and elite athletes. On the other hand, high carbohydrate avail-
ability during exercise training may result in improved body
composition, as gains in fat-free mass are amplified, whilst
fat loss is similar
(8)
. Hence, although there is a suggestion
that exercise in the fasted state can maximise some benefits
already associated with exercise, ensuing effects on appetite
and metabolism are not entirely clear.
The regulation of acute energy balance involves (not
exclusively) the exposure and sensitivity to the circulating
*Corresponding author: J. T. Gonzalez, fax þ44 191 243 7012, email javier.gonzalez@northumbria.ac.uk
Abbreviations: AUC
INS/GLU
, serum insulin AUC to blood glucose AUC ratio; BE, overnight fast followed by breakfast and exercise; BR, overnight fast
followed by breakfast and rest; FE, overnight fast followed by exercise without breakfast; FR, overnight fast followed by rest without breakfast; GLP-1,
glucagon-like peptide 1; ISI
Matsuda
, Matsuda insulin sensitivity index; VAS, visual analogue scale.
British Journal of Nutrition, page 1 of 12 doi:10.1017/S0007114512005582
qThe Authors 2013
British Journal of Nutrition
hormonal and metabolic milieu
(9)
, which underscores the
importance of determining these changes concomitant with
measuring energy balance. Exercise training improves glucose
tolerance
(5)
, yet acute exercise effects are less lucid
(10 – 13)
.
Muscle glucose uptake is increased after exercise
(14)
,as
assessed in rat hindlimb muscle. However, both this method
and the most commonly used technique for assessing insulin
sensitivity in human subjects (the euglycaemic hyperinsuli-
naemic clamp) possess some caveats. First, they ignore the
gastrointestinal response to food ingestion. Direct contact of
nutrients with L-cells in the intestine stimulates secretion of
glucagon-like peptide 1 (GLP-1), which potentiates insulin
secretion and sensitivity and reduces food intake
(9)
. GLP-1
exists in two active forms; in human subjects, the primary
circulating form is GLP-1
7–36(9)
. Acute exercise has been
shown to increase GLP-1 concentrations in the fed state
(15)
.
Therefore, GLP-1 may be an important mediator in the
acute regulation of energy homeostasis regarding breakfast
consumption and exercise.
Second, provision of nutrients other than glucose can
influence glucose tolerance and insulin sensitivity. Protein,
for example, stimulates insulin and/or incretin hormone
secretion
(16)
. Flavoured milk providing mixed macronutrients
is an increasingly consumed post-exercise drink due to its
recovery-enhancing potential
(17)
. Therefore, assessing the
whole-body metabolic and endocrine response to an orally
ingested mixed-nutrient load provides more applicable
findings to regular exercisers. Acute exercise can transiently
suppress hunger
(15,18)
, possibly via changes in appetite-related
hormones
(15,18,19)
. Subsequent relative energy intake is usually
also reduced
(18,19)
. The influence of nutritional status on
appetite regulation and energy intake following exercise is
not entirely understood. Of the studies investigating appetite
responses to fasted v. fed exercise, one used a high-fat
(70 %) meal
(20)
, which is not representative of a typical break-
fast, and another compared meal-exercise sequence rather
than omission of breakfast per se
(21)
.
Accordingly, the aim of the present study was to explore
the interaction of breakfast consumption and exercise on the
metabolic, endocrine and appetite responses to a commonly
consumed post-exercise drink, and to assess subsequent
energy intake and macronutrient balance in physically
active males.
Materials and methods
Participants
A group of twelve healthy males was recruited from the
student and staff population at Northumbria University
between December 2010 and April 2011. All participants
gave informed written consent and completed the entire
study. Participants who self-reported as physically inactive,
defined by less than 30 min of moderate activity, five times
per week by the International Physical Activity Question-
naire
(22)
; restrained eaters, defined by a score of .11 on
the Three Factor Eating Questionnaire
(23)
; or those with
any metabolic disorders or on medications were omitted.
The protocol was approved by the School of Life Sciences
Ethics Committee at Northumbria University.
Preliminary measurements
Participants undertook preliminary tests to establish: (1) the
relationship between O
2
uptake and running speed on a flat
treadmill (Woodway ELG, Woodway) using a four-stage,
16 min test; (2) their V
O2peak
using an incremental treadmill
test, whereby the gradient was increased by 1 %/min to
exhaustion, as described previously in detail
(24)
. The duration
of the exercise period in the main trials was calculated from
submaximal O
2
uptake and CO
2
values in order to expend
2·9 MJ (693 kcal) of energy whilst running at a speed estimated
to elicit 60 % V
O2peak
. This value was chosen to equate to
approximately 1 h on average, whilst maintaining similar
energy expenditure across participants. On the same day, par-
ticipants were familiarised with the visual analogue scales
(VAS) to assess subjective appetite sensations in main trials,
and it was verbally confirmed that participants did not have
any particular disliking of foods contained in the test meals.
Experimental design
All participants completed four trials in a randomised
(performed by J. T. G with Research Randomizer version 3.0;
http://www.randomizer.org/), crossover design separated by
$7 d comprising a continued overnight fast followed by:
(1) rest without breakfast (FR); (2) exercise without breakfast
(FE); (3) breakfast consumption (1859 kJ) followed by rest
(BR); and (4) breakfast consumption followed by exercise
(BE). By necessity of the design (food intake and exercise),
the intervention was not blinded. All trials were performed
under similar laboratory conditions (ambient temperature,
humidity and pressure; all P.0·05; data not shown). Food and
fluid diaries were kept for the day preceding the first trial and
participants were instructed to replicate this for all subsequent
trials. Alcohol, caffeine and vigorous activity were prohibited
for 24 h prior to trials.
On trial days, participants arrived in the laboratory at 07.30
hours after a 1014 h fast and a cannula was inserted into an
antecubital vein for blood sampling. After baseline samples of
expired gas and VAS were taken, in breakfast trials (BE and
BR), participants consumed a porridge breakfast. In fasting
trials (FE and FR), participants were permitted to consume
water only, which was consumed ad libitum on the first
exercise and non-exercise trials, and water consumption was
replicated for the following exercise and non-exercise trials
(Fig. 1). Following 120 min of rest, during exercise trials (BE
and FE), participants ran on a treadmill at 61·1 (SEM 0·6) %
V
O2peak
for 59 (SEM 2) min based on the a priori estimated
energy expenditure. Treadmill speed was adjusted accordingly
on the first trial to obtain the appropriate V
O2
. Changes in
speed were noted for duplication in subsequent exercise
trials. In resting trials (BR and FR), participants rested for the
equivalent amount of time as the exercise trials.
Within 20 min of exercise termination, participants ingested
a chocolate milk test drink. Following a 90 min postprandial
J. T. Gonzalez et al.2
British Journal of Nutrition
period, a homogeneous ad libitum test lunch was provided.
Participants were provided with an initial 430 g (3694 kJ;
882 kcal) portion of the test meal, which was replaced upon
completion. The test meal was terminated when the partici-
pant instructed that they felt ‘comfortably full’. Participants
were constantly reminded to follow this instruction and
were always presented with fresh, warmed portions before
participant-induced termination to ensure that the end of a
portion was not the reason for meal termination. Remaining
food was then removed and weighed out of the sight of the
participants to determine energy intake.
Anthropometric measurements
Body mass was determined to the nearest 0·1 kg using balance
scales (Seca) upon arrival at the laboratory, immediately prior
to and following exercise, where participants wore only light
clothing. Height was measured to the nearest 0·1 cm using a
stadiometer (Seca).
Test meals
The breakfast consisted of 72 g oats (Oatso Simple Golden
Syrup, Quaker Oats) and 360 ml semi-skimmed milk (Tesco)
and provided 1859 kJ of energy (444 kcal; 17 % protein, 60 %
carbohydrate and 23 % fat). The test drink was 500 ml of
chocolate milk (Yazoo, Campina Limited) and contained
1500 kJ of energy (358; 18 % protein, 63 % carbohydrate and
19 % fat). The test lunch comprised pasta (Tesco), tomato
sauce (Tesco), cheddar cheese (Tesco) and olive oil (Tesco)
and provided 859 kJ of energy per 100 g of food (205 kcal;
14 % protein, 52 % carbohydrate and 34 % fat).
Blood sampling and analysis
Blood samples, 10 ml, were collected at baseline, immediately
prior to and following exercise (or the equivalent points in
resting trials) at 15, 30, 50, 70 and 90 min following consump-
tion of the test drink (immediately prior to the test meal). All
samples were obtained whilst participants were seated upright
to control for postural changes in plasma volume. Additional
5 ml samples were collected at 5, 10, 20 and 25 min following
test drink ingestion, where blood glucose was determined
immediately by a glucose analyser (Biosen C_line, EKF
Diagnostics). From the 10 ml samples, a 20 ml capillary tube
was filled with whole blood to determine blood glucose
concentrations, 4 ml was dispensed into an EDTA vacutainer
containing 100 ml aprotinin and immediately centrifuged
at 3000 rpm at 48C for 10 min. Plasma was stored for later
determination of GLP-1
7–36
using an immunoassay (Phoenix
Pharmaceuticals, Inc.). Remaining whole blood from 10 ml
samples was allowed to stand for 30 min in a non-anticoagulant
tube before being centrifuged at 3000 rpm at 48C for 10 min.
Aliquots of serum were then stored for later determination of
NEFA (WAKO Diagnostics) and insulin (DIAsource Immuno-
Assays S.A.) concentrations in duplicate. All plasma/serum
samples were stored at 2808C. The intra-assay CV were 5·6
and 7·2 % for NEFA and insulin, respectively. Inter-assay CV
were 8·1, 3·6 and 18·5 % for NEFA, insulin and GLP-1
7–36
,
respectively. In order to reduce the inter-assay variation,
samples from each participant were analysed during the same
run where possible. It was decided that it was unnecessary to
adjust analyte concentrations to account for plasma volume
changes, as exercise of a similar and greater intensity and
duration does not result in changes in plasma volume
(15,25)
.
Energy expenditure and substrate oxidation
Expired gas samples were collected using an online gas
analysis system (Metalyzer 3B, Cortex) calibrated using gases
of known concentrations and a 3 l syringe. Participants wore a
facemask and after a 2 min stabilisation phase, 5 min samples
were obtained and averaged at baseline, at every 30 min after
breakfast consumption (or equivalent time in breakfast omis-
sion trials) and at 5, 15, 30, 50, 70 and 90 min following consump-
tion of the test drink. Expired gas was continuously sampled
throughout the exercise and averaged over each 5 min period,
ignoring the first 5 min to allow for steady-state values.
Substrate metabolism was calculated, assuming negligible
protein oxidation, with V
O2
and CO
2
production values using
stoichiometric equations and was adjusted during exercise to
account for the contribution of glycogen to metabolism
(26)
:
Rate of fat oxidation at rest and during exercise ðg=minÞ
¼ð1:695 £VO2 Þ2ð1:701 £VCO2Þ:
Rate of carbohydrate oxidation at rest ðg=minÞ
¼ð4:585 £VCO2 Þ2ð3:226 £VO2Þ:
Rate of carbohydrate oxidation during exercise ðg=minÞ
¼ð4:210 £VCO2Þ2ð2:962 £VO2Þ:
V
O2
and V
CO2
are measured in litres/min.
Energy expenditure was calculated based on fat, glucose
and glycogen concentrations providing 40·81, 15·64 and
17·36 kJ/g of energy, respectively. At rest, calculations were
based on glucose providing all of the carbohydrate for
metabolism, whereas during moderate-intensity exercise,
Visual analogue scales and expired
gas sample
Test
drink
Exercise
2 h rest
or
60 % VO2peak
2·9 MJ or
rest
15 30
Time (min)
50 70 90
Ad libitum
lunch
Fig. 1. Schematic representation of trials. , Breakfast consumption; , blood sample.
Integrated effects of breakfast and exercise 3
British Journal of Nutrition
carbohydrate oxidation is met by both glucose and glycogen
providing a 20 and 80 % contribution, respectively
(26)
.
Subjective ratings
Paper-based 100 mm VAS were completed at baseline, prior to
and immediately following breakfast and at every 30 min
thereafter until exercise (or equivalent time points in breakfast
omission trials); further, VAS were completed immediately
following exercise and after test drink consumption and at
30 min intervals thereafter. Final VAS were completed follow-
ing termination of the test meal. Questions asked were used
to determine hunger, fullness, satisfaction and prospective
food consumption. An overall appetite score was calculated
using the following formula, as previously used
(27)
:
Overall appetite
¼ðhunger þprospective food consumption
þð100 – fullnessÞþð100 – satisfactionÞÞ=4:
Statistical analysis
Due to difficulties associated with blood collection, data for
GLP-1
7–36
are presented from ten participants and, for all
other blood analytes, from eleven participants. After the
consumption of the test drink, glucose, insulin, GLP-1
7–36
and NEFA concentrations and appetite sensations were con-
verted into AUC using the trapezoidal rule. Indices of insulin
secretion and sensitivity, post-test drink serum insulin AUC
to blood glucose AUC ratio (AUC
INS/GLU
) and Matsuda insulin
sensitivity index (ISI
Matsuda
) were calculated as described pre-
viously
(28,29)
. Unless otherwise stated, all data are presented as
mean values with their standard errors. One-way, repeated
measures ANOVA was used to determine differences at base-
line, between all AUC values and total fat and carbohydrate
oxidation and energy expenditure between trials. Two-way
repeated measures ANOVA (trial £time) was used to detect
differences for all variables, and following a significant inter-
action effect, simple main effects analyses were employed.
This approach allowed for a comparison between the four
conditions (FR, FE, BR and BE) across time to determine
the most appropriate diet/exercise strategy. The Holm
Bonferroni step-wise post hoc test was utilised to determine
the location of the variance, and all Pvalues reported have
already been adjusted for multiple comparisons. Differences
were considered significant at P,0·05.
Results
The participants’ age, height, body mass, BMI and peak O
2
uptake (V
O2peak
) were 23·2 (SD 4·3) years, 178·0 (SD 7·0) cm,
77·2 (SD 5·3) kg, 24·5 (SD 2·0) kg/m
2
and 53·1 (SD 5·5) ml/kg
per min, respectively.
Blood glucose
Blood glucose concentration displayed a trial £time inter-
action effect (Fig. 2(A); P,0·001). Breakfast consumption
reduced time to reach peak blood glucose concentration
following test drink ingestion by 10 and 4 min during rest
and exercise trials, respectively (P¼0·012 and P¼0·02,
respectively). Peak blood glucose concentration was unaf-
fected by breakfast consumption during resting trials (FR:
5·95 (SEM 0·20) mmol/l, BR: 5·75 ( SEM 0·14) mmol/l; P¼0·20).
No difference was observed in peak or in time to peak
blood glucose concentrations in FR v. FE trials (P¼0·73 and
P¼0·28, respectively). However, in BE, blood glucose concen-
tration reached 6·66 (SEM 0·24) mmol/l, significantly greater
than FE (5·89 (SEM 0·17) mmol/l; P¼0·06) and BR (P¼0·030).
The difference between the BR and FR trials in AUC for
blood glucose approached statistical significance (Fig. 2(B);
P¼0·09); but it was not significantly different between
the FR and FE trials (P¼0·65); and was greater in BE v.BR
trials (P¼0·012).
FR BR FE BE
Trial
3·0
3·5
4·0
Time-averaged blood
glucose AUC (mmol/l)
Blood glucose
concentration (mmol/l)
4·5
5·0
(B)
(A)
3·0
BLPE 0 102030405060708090
Time post-drink (min)
*
*†§||
a,b,c
‡¶
*‡¶
‡||¶ ||
||
*
§
EX
b,c
b
a
3·5
4·0
4·5
5·0
5·5
6·0
6·5
Fig. 2. (A) Blood glucose concentration in response to test drink consumption
in the overnight fast followed by rest without breakfast (FR, W), overnight fast
followed by breakfast and rest (BR, X), overnight fast followed by exercise
(EX) without breakfast (FE, D) and overnight fast followed by breakfast and
EX (BE, O) trials. BL, baseline; PE, pre-EX. Values are means, with their
standard errors represented by vertical bars. * Mean value for the FE trial
was significantly different from that of BR trial (P,0·05). † Mean value for the
FR trial was significantly different from that of FE trial (P,0·05). ‡ Mean
value for the FR trial was significantly different from that of BE trial (P,0·05).
§ Mean value for the BR trial was significantly different from that of FE trial
(P,0·05). kMean value for the BR trial was significantly different from that of
BE trial (P,0·05). {Mean value for the FE trial was significantly different
from that of BE trial (P,0·05). (B) Time-averaged blood glucose AUC follow-
ing test drink consumption.
a,b,c
Values with unlike letters were significantly
different (P,0·05).
J. T. Gonzalez et al.4
British Journal of Nutrition
Serum insulin
A trial £time interaction effect was observed for serum
insulin concentrations (P,0·001), where peak concentrations
occurred at 37 (SEM 3) min in the FR trial, and the delay
compared with BR (29 (SEM 1) min; P¼0·09) and FE
(30 (SEM 4) min; P¼0·10) approached statistical significance.
Serum insulin concentrations rose after test drink consump-
tion (Fig. 3(A)) to a similar peak between trials (FR: 682
(SEM 71), BR: 607 (SEM 46), FE: 570 (SEM 72) and BE: 586 (SEM
64) pmol/l; P¼0·21). The greater AUC for serum insulin in FR
v. all other trials approached statistical significance (Fig. 3(B);
P¼0·07, P¼0·12 and P¼0·09 for BR, FE and BE, respectively).
Indices of insulin secretion and sensitivity
The AUC
INS/GLU
was similar between FR and BR trials (82
(SEM 7) and 80 (SEM 6) pmol/mmol; P¼0·45), but was reduced
by exercise compared with the FR trial (FE: 70 (SEM 7) and BE:
67 (SEM 6) pmol/mmol; P¼0·03 and P¼0·04 for FE and BE
trials, respectively). ISI
Matsuda
was similar between the trials
(12 (SEM 4), 12 (SEM 4), 12 (SEM 4) and 13 (SEM5) arbitrary units
for FR, BR, FE and BE respectively; all P.0·05).
Serum NEFA
Test drink consumption transiently suppressed NEFA concen-
trations and a significant trial £time interaction effect was
observed (Fig. 4(A); P,0·001). The time at which the nadir of
NEFA concentrations was reached was delayed in the FR trial (81
(SEM 3) min) compared with all other trials (BR: 65 (SEM 3) min,
P¼0·019; FE: 57 (SEM 3) min, P,0·001; and BE: 55 (SEM 6) min,
P¼0·007). The AUC for BR was lower than that for FR and
BE trials (Fig. 4(B); P¼0·019 and P¼0·004, respectively).
Plasma glucagon-like peptide 1
7–36
There was no trial £time interaction effect or main effects of
trial on GLP-1
7–36
concentrations (Fig. 5(A); both P.0·05).
FR BR FE BE
Trial
0·0
0·1
Time-averaged serum
NEFA AUC (mmol/l)
Serum NEFA
concentration (mmol/l)
0·2
0·3
0·4(B)
(A)
0·0
BLPE 0 102030405060708090
Time post-drink (min)
*
§
*§||
*|| ‡||
a
EX
a,b,c a,c
b
0·1
0·2
0·3
0·4
0·5
0·6
0·7
Fig. 4. (A) Serum NEFA concentration in response to test drink consumption
in the overnight fast followed by rest without breakfast (FR, W), overnight fast
followed by breakfast and rest (BR, X), overnight fast followed by exercise
(EX) without breakfast (FE, D) and overnight fast followed by breakfast and
EX (BE, O) trials. BL, baseline; PE, pre-EX. Values are means, with standard
errors represented by vertical bars. * Mean value for the FE trial was signifi-
cantly different from that of BR trial (P,0·05). † Mean value for the FR trial
was significantly different from that of FE trial (P,0·05). ‡ Mean value for the FR
trial was significantly different from that of BE trial (P,0·05). § Mean value for
the BR trial was significantly different from that of FE trial (P,0·05). kMean
value for the BR trial was significantly different from that of BE trial (P,0·05).
{Mean value for the FE trial was significantly different from that of BE trial
(P,0·05). (B) Time-averaged serum NEFA AUC following test-drink consump-
tion.
a,b,c
Values with unlike letters were significantly different (P,0·05).
FR BR FE BE
Trial
BLPE 0 102030405060708090
Time post-drink (min)
*
§
§
||
EX
*‡
*
*‡§
*द
Time-averaged serum
insulin AUC (pmol/l)
Serum insulin
concentration (pmol/l)
0
100
200
300
400
0
100
200
300
400
500
600
700
(B)
(A)
Fig. 3. (A) Serum insulin concentration in response to test drink consumption
in the overnight fast followed by rest without breakfast (FR, W), overnight fast
followed by breakfast and rest (BR, X), overnight fast followed by exercise
(EX) without breakfast (FE, D) and overnight fast followed by breakfast and
EX (BE, O) trials. BL, baseline; PE, pre-EX. Values are means, with standard
errors represented by vertical bars. * Mean value for the FE trial was signifi-
cantly different from that of BR trial (P,0·05). † Mean value for the FR trial
was significantly different from that of FE trial (P,0·05). ‡ Mean value for the
FR trial was significantly different from that of BE trial (P,0·05). § Mean
value for the BR trial was significantly different from that of FE trial (P,0·05).
kMean value for the BR trial was significantly different from that of BE trial
(P,0·05). {Mean value for the FE trial was significantly different from that of
BE trial (P,0·05). (B) Time-averaged serum insulin AUC following test-drink
consumption.
Integrated effects of breakfast and exercise 5
British Journal of Nutrition
There was also no difference in AUC (Fig. 5(B)), peak or
time to peak GLP-1
7–36
concentrations (P¼0·17, P¼0·27 and
P¼0·45, respectively).
Energy intake, metabolism and balance
Energy expenditure, fat oxidation and carbohydrate oxidation
did not differ at baseline (P¼0·43, P¼0·13 and P¼0·57,
respectively).
In the breakfast postprandial period, energy expenditure
was not significantly different between the trials (Table 1).
Less fat and more carbohydrate were utilised during the break-
fast postprandial period in the breakfast trials (i.e. BE and BR)
v. fasting trials (i.e. FE and FR) (Table 1; P¼0·005 and
P,0·001, respectively).
The exercise bout lasted for 59 (SEM 2) min and mean O
2
uptake was similar between the FE and BE trials during
this period (2·52 (SEM 0·11) and 2·50 (SEM 0·11) litres/min;
P¼0·54). In spite of the equivalent amount of external work
performed, exercise increased energy expenditure more
during the breakfast trials (3279 (SEM 50) kJ) compared
with that during the fasting trials (2627 (SEM 43) kJ; P,0·01).
Breakfast consumption reduced the reliance on fat as a
substrate and subsequently raised carbohydrate metabolism
in the exercise period, an effect which was independent of
exercise/rest (Table 1). This resulted in similar carbohydrate
balance (intake minus oxidation) post-exercise between FE
and BE, in spite of a large difference in carbohydrate balance
prior to exercise (pre-exercise: 217 (SEM 2) and 43 (SEM 2) g,
P,0·001; post-exercise: 2108 (SEM 7) and 2102 (SEM 8) g,
P¼0·38 for FE and BE trials, respectively). Following con-
sumption of the test drink, energy expenditure and fat
oxidation were greater in both exercise trials compared with
rest trials, yet carbohydrate oxidation was similar (Table 1).
There was no detectable difference in ad libitum energy
intake at lunch (Fig. 6; P¼0·78). Hence, when energy intakes
from the breakfast and the test drink are taken into consider-
ation, breakfast trials produced a greater total energy intake
(Fig. 6; P,0·001). The variation in the compensation of
energy intake to account for the increase in energy expenditure
(energy intake on exercise trials minus energy intake on resting
trials) ranged from 21916 to 3749 kJ (2458 to 895 kcal) in the
fasting trials and from 21447 to 3683 kJ (2346 to 880 kcal) in
the breakfast trials. A total of seven individuals consumed
less in the FE v. FR trial, four individuals partially compensated
for exercise, consuming more in the FE v. FR trial, but not
enough to overcome the exercise-induced energy expenditure.
Only one participant over-compensated for exercise, consum-
ing more than the exercise-induced energy expenditure in
the FE v. FR trial. In breakfast trials, six individuals consumed
less in the BE v. BR trial, five partially compensated and only
one over-compensated for the exercise-induced energy expen-
diture. No significant relationship was present between the
compensation on fast days and the compensation on breakfast
days (r20·07, P.0·05).
Energy balance post-lunch was most positive with BR and
least positive with FE trials (Fig. 7). There was no detectable
difference in carbohydrate balance when breakfast was omitted
v. consumed, although the difference at rest approached
significance (FR v. BR, P¼0·06; FE v. BE, P¼0·95; Fig. 7). Yet,
fat balance was significantly different between all trials, apart
from the FR v. BE trial, albeit in BE, a reduction which
approached statistical significance was observed (P¼0·06).
Subjective ratings
Feelings of hunger during the exercise period were
suppressed in FE v.FR(P¼0·015) and BE v. BR trials
(P¼0·016). This was still the case immediately post-exercise
in the FE v. FR trial (P¼0·002), yet, in the BE v. BR trial,
there was no detectable difference (P¼0·45). FE also reduced
ratings of prospective consumption during and after exercise
v.FR(P¼0·028 and P¼0·032, respectively), whereas BE did
not significantly affect prospective consumption ratings com-
pared with BR (P¼0·67 and P¼0·15, respectively). Overall
appetite rating showed similar findings (Fig. 8(A)), where
the change from pre- to during the exercise period was signifi-
cantly different between the FR and the FE trials (2 (SEM 1) v.
211 (SEM 4); P¼0·048), but not between the BR and BE trials
(6 (SEM 2) v.0(SEM 4); P¼0·21).
Breakfast did not influence hunger immediately pre-
lunch during exercise trials (P¼0·11), but did reduce hunger
FR BR FE BE
Trial
Time post-drink (min)
BLPE 0 102030405060708090
EX
Time-averaged plasma
GLP-17–36 AUC (pmol/l)
Plasma GLP-17–36
concentration (pmol/l)
0
20
15
10
5
0
15
10
5
(B)
(A)
Fig. 5. (A) Plasma glucagon-like peptide-1
7–36
(GLP-1
7–36
) concentration
in response to test drink consumption in the overnight fast followed by rest
without breakfast (FR, W), overnight fast followed by breakfast and rest
(BR, X), overnight fast followed by exercise (EX) without breakfast (FE, D)and
overnight fast followed by breakfast and EX (BE, O) trials. BL, baseline; PE,
pre-EX. (B) Time-averaged GLP-1
7–36
AUC following test drink consumption.
Values are means, with standard errors represented by vertical bars.
J. T. Gonzalez et al.6
British Journal of Nutrition
in resting trials (P¼0·006). The same pattern was
observed with prospective consumption (FR v. BR: P¼0·005;
BR v. FE: P¼0·005; FE v. BE: P¼0·10). However, immediately
prior to lunch, overall appetite was suppressed in the BR
trial compared with that in both fasting trials (i.e. FE
and FR) (P¼0·001 and P¼0·005, for rest and exercise, respect-
ively; Fig. 8(B)).
There was no detectable difference in AUC for hunger
between exercise and rest (P¼0·47 and P¼0·71 for FR v.FE
and BR v. BE trials, respectively). The AUC for overall appetite
following consumption of the test drink was greater in the FR
trial v. the BR trial (Table 2; P¼0·006), and this pattern was
still apparent, although it was attenuated when exercise was
performed (Table 2; P¼0·029). Similar patterns were shown
for hunger and prospective consumption AUC and mirrored
by fullness and satisfaction AUC (Table 2).
Discussion
The present study attempted to examine the cumulative effects
of breakfast consumption and exercise on the metabolic and
appetite responses to foods consumed later in the day and on
subsequent energy and macronutrient balance. The main find-
ings were that acute breakfast consumption is likely to reduce
postprandial glycaemia and insulinaemia at rest. Acute exercise
did not affect glucose tolerance when breakfast was omitted,
but reduced glucose tolerance when breakfast was consumed;
the pertinence of this chronically should be noted with cau-
tion, given the benefits of exercise training. Exercise in the
fasted state led to a greater transitory reduction in appetite
compared with exercise in the fed state. Energy and fat bal-
ance were least positive following exercise in the fasted state.
Acute breakfast consumption has been shown to improve
glucose tolerance
(2)
. The present findings in physically active
males somewhat support the previous data, although the
effect may be more trivial in these aerobically fit individuals,
with magnitude-based inferences
(30)
indicating 41 and 59 %
likelihoods of beneficial and negligible effects, respectively,
on glucose tolerance. This could be due to the fact that
subjects in the present study are regular exercisers and therefore
displaying better basal glucose tolerance
(5)
. Lower fasting blood
glucose concentrations (approximately 4·5 v. 4·8 mmol/l)
support this proposition. Lower NEFA exposure prior to con-
sumption of the test drink in the BR trial compared with the
FR trial is a possible cause of the potential improvement
in glucose tolerance, as prolonged NEFA elevations reduce
insulin-stimulated glucose disposal by inhibiting insulin signal-
ling
(31)
. The (non-significant) increase in insulinemia and delay
in peak insulin concentrations do support this proposition.
Muscle contraction stimulates insulin-independent glucose
uptake
(14)
, and thus explains why glucose uptake is augmen-
ted following an acute bout of exercise in spite of increased
NEFA concentrations, which was observed in the FE and
BE trials. Increased glucose uptake is a well-established
observation at the muscle
(14)
and whole-body level
(32)
. Thus,
based on insulin clamp studies, it may seem surprising
that there was no difference in glucose tolerance between
the fasted rest and exercise trials, but this does, in fact,
Table 1. Energy expenditure and substrate metabolism during the breakfast postprandial period, exercise or the equivalent rest period and the recovery period following test drink consumption
(Mean values with their standard errors)
Breakfast period (120 min) Exercise period (about 60 min) Recovery period (90 min)
EE (kJ) FO (g) CO (g) EE (kJ) FO (g) CO (g) EE (kJ) FO (g) CO (g)
Trial Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM
FR 919 90 17·4 1·9 13·5 2·8 377 25 7·3 0·8 5·0 0·9 754 4 12·6 1·6 15·5 2·0
BR 922 61 12·4* 1·5 26·6* 2·5 376 20 5·9* 0·8 8·6* 1·1 775 47 11·1 1·2 20·5 2·1
FE 875 46 15·0 1·4 16·8† 1·8 3003*† 43 35·3*† 3·1 91·7*† 7·0 831* 37 15·3† 1·2 13·2 1·8
BE 946 60 13·8* 1·8 24·3a 2·4 3655*†‡ 47 29·3*†‡ 3·2 144·6*†‡ 7·6 832* 37 14·7† 1·5 14·9 2·2
EE, energy expenditure; FO, fat oxidation; CO, carbohydrate oxidation; FR, overnight fast followed by rest without breakfast; BR, overnight fast followed by breakfast and rest; FE, overnight fast followed by exercise without
breakfast; BE, overnight fast followed by breakfast and exercise.
* Mean value was significantly different from FR (P,0·05).
Mean value was significantly different from BR (P,0·05).
Mean value was significantly different from FE (P,0·05).
Integrated effects of breakfast and exercise 7
British Journal of Nutrition
corroborate with studies using oral glucose tolerance tests.
Until now, studies in healthy participants have shown either
decreases
(10,11,33 – 37)
or no difference
(12,13,38)
in glucose toler-
ance following acute endurance exercise. In those displaying
no difference, the tests were either performed in the fasted
state
(13,38)
or glucose tolerance was assessed more than 2 h
after exercise
(12)
. The present study is the first to demonstrate
that when nutrients are ingested immediately post-exercise,
the effect on acute postprandial glucose kinetics may
depend on the nutritional state (fasted or fed) prior to exercise.
It may be the accrual of this acute effect that contributes to the
attenuated improvements in glucose tolerance seen during
exercise training when carbohydrate availability is high
(5)
.
Regarding the effects of exercise when fasted, endurance
exercise increases the rate of appearance of endogenous
glucose
(37)
. Therefore, the increase in muscle glucose uptake
after exercise
(14)
(affecting rate of disappearance) could
ostensibly be offset by the increase in splanchnic glucose
output (affecting rate of appearance) and, hence, result in
an increase in flux, but there was no difference in the systemic
concentrations of glucose after exercise compared with that
after rest when fasted. Future studies are needed to address
whether this is indeed the mechanism at play.
Food consumption prior to exercise also increases splanch-
nic blood flow during exercise
(6)
. As mesenteric blood flow
is positively associated with intestinal glucose absorption
(39)
,
it can be speculated that the increase in blood flow (from
breakfast consumption), combined with increased passive
absorption (from exercise), results in the greater peak blood
glucose concentration in the BE trial compared with the FE
trial. However, recent evidence associates the increase in
intestinal absorption with reduced gut blood flow occurring
during intense exercise and may result in intestinal
damage
(40)
, indicating faster entry of glucose into the circula-
tion when gut blood flow is reduced (which occurs when
exercising after fasting compared with after feeding
(6)
).
This adds to the confusion in the previous conjecture, as the
putative increase in splanchnic blood flow in BE would
result in less intestinal cell damage and reduced passive
absorption, leading to a lower blood glucose AUC (assuming
that endogenous glucose production and glucose disappear-
ance remain constant, which can be presumed due to similar
carbohydrate balance post-exercise and thus similar whole-
body glycogen concentrations).
The present study used an exercise intensity that was lower
(61 % V
O2peak
v. 70 % of maximum power output) than that of
van Wijck et al.
(40)
. At lower intensities (55 % V
O2peak
), the
exercise-induced reduction in splanchnic blood flow is abol-
ished
(6)
. This makes it tempting to presume that other factors,
such as heat or mechanical stresses or changes in hormone
concentrations, contribute to the increase in intestinal glucose
absorption following exercise
(41)
. Another factor at play could
be reductions in insulin sensitivity of non-exercised (upper
limb) muscle following exercise
(42)
. Clearly, this area has
great scope for future work, pertinent to the understanding
of the impact of food intake and exercise on subsequent
whole-body glucose tolerance.
The AUC
INS/GLU
was lower in both exercise trials com-
pared with the FR trial, whereas ISI
Matsuda
was similar between
trials, suggesting that postprandial insulin secretion is reduced
immediately following exercise, but insulin sensitivity is
unaffected
(28,29)
. This strengthens the assumption that the
change in glucose kinetics seen in the present study is due
to a difference in the glucose rate of appearance.
The finding that GLP-1
7–36
concentrations were not differ-
ent between trials is in accordance with the proposition that
glucose entered the circulation via passive absorption. Intrave-
nous infusion of glucose mirroring the plasma glucose profile
to oral ingestion does not augment GLP-1 concentrations
(43)
.
Therefore, as GLP-1
7–36
concentrations were not different
between trials, this provides support for elevated glucose
appearance from passive absorption, as greater GLP-1
7–36
secretion would not occur. GLP-1
7–36
is also a potent incretin
a
a
a
a
b
b
c
c
b
a
d
7000
6000
5000
4000
3000
2000
1000
0
FR
Substrate balance (kJ)
BR FE BE
Trial
b
Fig. 7. Substrate balance. Carbohydrate ( ), fat ( ) and energy ( and
combined) balance at the end of the trial. FR, overnight fast followed by rest
without breakfast; BR, overnight fast followed by breakfast and rest; FE,
overnight fast followed by exercise without breakfast; BE, overnight fast fol-
lowed by breakfast and exercise. Values are means, with standard errors
represented by vertical bars.
a,b,c,d
Values with unlike letters were significantly
different (P,0·05).
10 000
a
b
a
b
8000
6000
4000
2000
0FR
Energy intake (kJ)
BR FE BE
Trial
Fig. 6. Energy intake. Energy intake at lunch ( ) and throughout the whole
trial ( ). FR, overnight fast followed by rest without breakfast; BR, overnight
fast followed by breakfast and rest; FE, overnight fast followed by exercise
without breakfast; BE, overnight fast followed by breakfast and exercise.
Values are means, with standard errors represented by vertical bars.
a,b
Values with unlike letters were significantly different (P,0·05).
J. T. Gonzalez et al.8
British Journal of Nutrition
hormone, stimulating insulin secretion and also suppressing
appetite
(9)
. Thus, as GLP-1
7–36
concentration did not differ
between trials, it would seem that other factors are playing a
role in enhanced insulin action and appetite suppression with
breakfast consumption. It should be noted that GLP-1
7–36
may interact with neurons expressed locally in L-cells, prior
to being rapidly degraded on entry into the circulation,
where its clearance can exceed cardiac output by two to
three times
(44)
. Hence, GLP-1
7–36
can still influence appetite
in spite of no detectable rise in its plasma concentrations.
There was evidence of delayed suppression of NEFA follow-
ing consumption of the test drink in the FR trial compared
with the BR trial, suggestive of metabolic inflexibility, again
associated with insulin resistance. Exercise uncoupled the
link between breakfast, NEFA and insulin concentrations,
whereby, in both the FE and BE trials, insulin and NEFA con-
centrations were similar prior to and following consumption
of the test drink. Increased NEFA availability during and
following exercise is required to support higher rates of fat
oxidation by skeletal muscle as carbohydrate is used to
replenish glycogen stores
(11)
. As such, NEFA flux is raised,
and, as insulin-resisting effects of NEFA on muscle seem to
be time dependent
(31)
, turnover may be more important
than NEFA concentrations for insulin sensitivity.
Exercise transiently suppressed hunger and overall appetite.
This is a common phenomenon
(15,18,45)
, yet less is known
about the effect of nutritional status on the ability of exercise
to influence appetite. The present study found that, compared
with rest, exercise suppressed hunger and overall appetite
to a greater extent when fasted compared with the fed state
(approximately 17 v. 9 %, respectively). Nevertheless, it
should be noted that appetite was higher in the fasting state
prior to exercise. To our knowledge, this is the first crossover
study to demonstrate the effect of exercise in fasted and fed
conditions on appetite sensations compared with resting
trials in the equivalent nutritional state.
Harmonious with preceding research
(15,18)
, the exercise-
induced suppression of appetite was abolished within
30 min of exercise termination and appetite was subsequently
similar between exercise and rest trials until lunch. Breakfast
consumption, however, reduced overall appetite following
test drink consumption by approximately 17 and 14 % in the
rest and exercise trials, respectively. Despite a 10 % reduction
in appetite ratings with breakfast consumption, no detectable
difference in energy intake between trials was observed at
lunch. This occurred regardless of the additional 1859 kJ
of energy consumed during breakfast and approximately
2423 kJ of energy expended during exercise. Subsequently,
energy intake was higher in breakfast trials. Observational
data corroborate the present findings with daily energy
intake increase in regular breakfast consumers compared
with omitters
(1)
. Yet, when BMI was measured, it was still
inversely associated with breakfast consumption
(1)
, suggesting
that it may be the increased energy expenditure and the
improved metabolic responses to food consumption that
result in better weight maintenance.
The outcome that exercise did not influence subsequent
energy intake is in accord with most of the prior research in
this area, although some have found an increase in immediate
energy intake
(46)
. It may be that individual variation exists,
whereby some individuals’ drive to eat following exercise is
dominated by hedonic processes
(47)
. This leads to a diver-
gence between those who compensate for extra energy
expenditure by increasing intake and non-compensators,
who fail to increase intake in the face of an increase in expen-
diture. In the present study, the range of compensation for
exercise-induced energy expenditure was large (5665 kJ of
energy separated the individual who over-compensated and
the individual who under-compensated the greatest). This
variation in the compensation of energy expenditure is likely
to account for the variation seen in body fat changes in an
exercise intervention (reviewed by Caudwell et al.
(48)
). It is
interesting to note that there was no significant relationship
between the degree of compensation to exercise on fasted
trials and breakfast trials, suggesting that those who over-
compensate during exercise in one nutritional state (i.e. the
100 *द
*†‡
§¶ *‡§
80
60
40
20
0
0 20406080100
Time post-drink (min)
Overall appetite (mm)
**‡§
Time (min)
(A)
100
80
60
40
20
0
Overall appetite (mm)
(A)
BL 0 30 60 90 120 DE EE
EX
Breakfast postprandial period
*
Fig. 8. Overall appetite. Overall appetite sensations during (A) the breakfast
postprandial and exercise (EX) periods and (B) following test drink consump-
tion in the overnight fast followed by rest without breakfast (FR, W), overnight
fast followed by breakfast and rest (BR, X), overnight fast followed by EX
without breakfast (FE, D) and overnight fast followed by breakfast and EX
(BE, O) trials. BL, baseline; DE, during EX; EE, end of EX; PL, post-lunch.
Values are means, with standard errors represented by vertical bars. * Mean
value for the FE trial was significantly different from that of BR trial (P,0·05).
† Mean value for the FR trial was significantly different from that of FE trial
(P,0·05). ‡ Mean value for the FR trial was significantly different from that of
BE trial (P,0·05). § Mean value for the BR trial was significantly different
from that of FE trial (P,0·05). {Mean value for the FE trial was significantly
different from that of BE trial (P,0·05).
Integrated effects of breakfast and exercise 9
British Journal of Nutrition
fasted/fed state) may not over-compensate in the opposing
circumstance. Another possibility is that exercise energy
expenditure is gradually compensated for by energy intake,
which is likely to require a period of several weeks, and
even then is not likely to be fully compensated for
(49)
.
The higher total energy intake with breakfast trials and the
exercise-induced energy expenditure led to energy balance
being most positive in the BR trial and least positive in the FE
trial. BE resulted in an approximately 1110 kJ reduction in
energy balance compared with FR. When taken in concert
with the similar appetite sensations to resting trials, exercise
may provide a more attractive option for restricting energy avail-
ability compared with omitting breakfast. Interestingly, in spite
of differing quantities of carbohydrate and fat oxidised with all
trials, carbohydrate balance was remarkably similar between
the FE and BE trials, whereas fat balance was 3-fold more posi-
tive in the BE trial. This may not be as clear at rest, as the differ-
ence between the FR and BR trials in carbohydrate balance did
approach a statistically significant difference (Fig. 7), but was
higher than that in exercise trials. At least in the short term,
the regulation of carbohydrate stores is more tightly regulated
than fat stores
(19)
. The findings of the present study add that
consumption/omission of breakfast will not alter carbohydrate
balance, whereas exercise can reduce carbohydrate balance.
The increased energy expenditure observed during
exercise with breakfast consumption was provided by a
higher rate of carbohydrate oxidation, this has previously
been reported
(50 – 52)
and may be magnified during running
due to the weight-bearing component
(53)
. The relevance of
this with respect to energy balance was, however, trivial,
as energy balance was lower in the FE trial compared with
the BE trial.
This controlled experimental study involved the provision
of a popular breakfast food consumed prior to a bout of exer-
cise or rest in physically active males, with a structure similar
to the eating patterns in Western society. It could be viewed
that a caveat with the present study is that the participants
were physically active and that a sedentary population
would benefit more from exercise/diet-induced improvements
in metabolism and appetite. However, those who regularly
exercise still utilise energy/carbohydrate restriction in order
to regulate body composition
(4)
. Therefore, the results are
pertinent to these populations; yet, it would undoubtedly be
of virtue to investigate these responses in other populations
(females, sedentary and obese) to extrapolate findings to a
wider population. Moreover, future work should examine
whether there is a difference in energy intake in subsequently
consumed meals over a longer duration.
It is also of merit to recognise that the environmental
conditions were similar between trials, which is important
due to the potential effect of temperature on appetite and
energy intake
(46)
.
The findings of the present investigation suggest that in
an acute setting, energy intake from breakfast and energy
expenditure from exercise are not compensated for at lunch.
Consequently, energy balance was most positive following
breakfast and rest and least positive following breakfast
omission and exercise. When exercise is performed, it may
be more pertinent to omit breakfast if a negative fat balance
is desirable, although the findings of the present study are
unable to predict the longer-term outcomes of energy and
fat balance due to the single-meal design, and as such this
conclusion should be interpreted with caution.
The present study aimed to explore the effect of breakfast
and exercise on the metabolic and appetite responses to
subsequent food consumption. The findings indicate that
breakfast ingestion may improve the metabolic and appetite
responses to subsequently consumed foods when sedentary.
When breakfast is consumed, subsequent postprandial
glycaemia is higher following exercise, yet care should
be taken during the interpretation for chronic effects, as
exercise training almost always confers a benefit for glucose
tolerance and insulin sensitivity. Exercise also resulted in
an ephemeral reduction in appetite, which is greater when
performed fasted.
Acknowledgements
We gratefully thank the volunteers for their participation and
A. Wilde for technical assistance. This project received no
external funding. J. T. G. and E. J. S. designed the study, J. T.
G. and R. C. V. performed the data collection and all authors
contributed to data analysis and interpretation and writing of
the manuscript. The authors declare no conflicts of interest.
Table 2. Time-averaged AUC values for subjective appetite responses to consumption of the test drink
(Mean values with their standard errors)
Hunger (mm) Fullness (mm)
Satisfaction
(mm)
Prospective
consumption
(mm)
Overall appe-
tite (mm)
Trial Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM
FR 65 4 30 4 27 2 72 3 70 2
BR 54* 4 40 4 40* 3 58* 4 58* 3
FE 63 3 28† 4 29† 3 68† 4 67† 3
BE 55 4 40 4 40*‡ 3 62* 4 59*‡ 4
FR, overnight fast followed by rest without breakfast; BR, overnight fast followed by breakfast and rest; FE, overnight fast
followed by exercise without breakfast; BE, overnight fast followed by breakfast and exercise.
* Mean value was significantly different from FR (P,0·05).
Mean value was significantly different from BR (P,0·05).
Mean value was significantly different from FE (P,0·05).
J. T. Gonzalez et al.10
British Journal of Nutrition
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J. T. Gonzalez et al.12
British Journal of Nutrition
... With the exception of one study which provided a notably small breakfast (~ 250 kcal) [15], breakfast omission studies show that the energy deficit created by omitting breakfast is not fully compensated for at lunch, and, as such, cumulative energy intake is reduced compared to when breakfast is consumed [9,10,12,16,29]. This was also the case in this study, as, compared to FOOD, cumulative energy intake was approximately 477 and 461 kcal lower during PLA and WAT. ...
... This is consistent with previous studies, which have reported an increase in lunch energy intake of between 153 and 206 kcal following breakfast omission, compared to when a breakfast containing ~ 250-733 kcal was consumed [10,12,15,16]. Some studies, however, have reported a similar energy intake at lunch following breakfast omission and consumption [9,16,29]. Inconsistencies in these findings may result from methodological differences between studies, such as differences in the time interval between breakfast and lunch, and/or the method employed to assess ad libitum energy intake (i.e. a homogenous, singleitem meal versus a multi-item buffet meal). ...
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Purpose This study aimed to assess the effects of consuming a very-low-energy placebo breakfast on subsequent appetite and lunch energy intake. Methods Fourteen healthy males consumed water-only (WAT), very-low-energy, viscous placebo (containing water, low-calorie flavoured squash, and xanthan gum; ~ 16 kcal; PLA), and whole-food (~ 573 kcal; FOOD) breakfasts in a randomised order. Subjects were blinded to the energy content of PLA and specific study aims. Venous blood samples were collected pre-breakfast, 60- and 180-min post-breakfast to assess plasma acylated ghrelin and peptide tyrosine tyrosine concentrations. Subjective appetite was measured regularly, and energy intake was assessed at an ad libitum lunch meal 195-min post-breakfast. Results Lunch energy intake was lower during FOOD compared to WAT ( P < 0.05), with no further differences between trials ( P ≥ 0.132). Cumulative energy intake (breakfast plus lunch) was lower during PLA (1078 ± 274 kcal) and WAT (1093 ± 249 kcal), compared to FOOD (1554 ± 301 kcal; P < 0.001). Total area under the curve (AUC) for hunger, desire to eat and prospective food consumption were lower, and fullness was greater during PLA and FOOD compared to WAT ( P < 0.05). AUC for hunger was lower during FOOD compared to PLA ( P < 0.05). During FOOD, acylated ghrelin was suppressed compared to PLA and WAT at 60 min ( P < 0.05), with no other hormonal differences between trials ( P ≥ 0.071). Conclusion Consuming a very-low-energy placebo breakfast does not alter energy intake at lunch but may reduce cumulative energy intake across breakfast and lunch and attenuate elevations in subjective appetite associated with breakfast omission. Trial registration NCT04735783, 2nd February 2021, retrospectively registered.
... Expression of purported molecular clock genes exhibits an individualized diurnal variation, which correlates with muscular strength exercise performance and the clock itself (Kemler et al., 2020;Basti et al., 2021). The timing of exercise remains a controversial topic, with some investigators favoring morning exercise to enhance muscle adaptations and fuel utilization (Bennard and Doucet, 2006;Van Proeyen et al., 2010;Gonzalez et al., 2013;Ezagouri et al., 2019;Sato et al., 2019;Willis et al., 2020); whereas, others have shown afternoon/evening exercise is most favorable to improve muscle function (Bernard et al., 1998;Racinais, 2010;Chtourou and Souissi, 2012;Küüsmaa et al., 2016). In either case, research exploring potential effects of exercise time of day (ETOD) on training-induced adaptations remains to be fully chartered within multiple domains of "real-life" applicability, warranting examination. ...
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The ideal exercise time of day (ETOD) remains elusive regarding simultaneous effects on health and performance outcomes, especially in women. Purpose: Given known sex differences in response to exercise training, this study quantified health and performance outcomes in separate cohorts of women and men adhering to different ETOD. Methods: Thirty exercise-trained women (BMI = 24 ± 3 kg/m ² ; 42 ± 8 years) and twenty-six men (BMI = 25.5 ± 3 kg/m ² ; 45 ± 8 years) were randomized to multimodal ETOD in the morning (0600–0800 h, AM) or evening (1830–2030 h, PM) for 12 weeks and analyzed as separate cohorts. Baseline (week 0) and post (week 12) muscular strength (1-RM bench/leg press), endurance (sit-ups/push-ups) and power (squat jumps, SJ; bench throws, BT), body composition (iDXA; fat mass, FM; abdominal fat, Abfat), systolic/diastolic blood pressure (BP), respiratory exchange ratio (RER), profile of mood states (POMS), and dietary intake were assessed. Results: Twenty-seven women and twenty men completed the 12-week intervention. No differences at baseline existed between groups (AM vs PM) for both women and men cohorts. In women, significant interactions ( p < 0.05) existed for 1RM bench (8 ± 2 vs 12 ± 2, ∆kg), pushups (9 ± 1 vs 13 ± 2, ∆reps), BT (10 ± 6 vs 45 ± 28, ∆watts), SJ (135 ± 6 vs 39 ± 8, ∆watts), fat mass (−1.0 ± 0.2 vs −0.3 ± 0.2, ∆kg), Abfat (−2.6 ± 0.3 vs −0.9 ± 0.5, ∆kg), diastolic (−10 ± 1 vs−5 ± 5, ∆mmHg) and systolic (−12.5 ± 2.7 vs 2.3 ± 3, mmHg) BP, AM vs PM, respectively. In men, significant interactions ( p < 0.05) existed for systolic BP (−3.5 ± 2.6 vs −14.9 ± 5.1, ∆mmHg), RER (−0.01 ± 0.01 vs −0.06 ± 0.01, ∆VCO 2 /VO 2 ), and fatigue (−0.8 ± 2 vs −5.9 ± 2, ∆mm), AM vs PM, respectively. Macronutrient intake was similar among AM and PM groups. Conclusion: Morning exercise (AM) reduced abdominal fat and blood pressure and evening exercise (PM) enhanced muscular performance in the women cohort. In the men cohort, PM increased fat oxidation and reduced systolic BP and fatigue. Thus, ETOD may be important to optimize individual exercise-induced health and performance outcomes in physically active individuals and may be independent of macronutrient intake.
... Data are presented as individual measured responses across time (a) and using the incremental AUC summary statistic displayed as mean ± 95% CI with individual measured responses (b). Real experimental data for nine participants extracted from Gonzalez et al. (2013). AUC = area under the curve; CI = confidence interval. ...
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The analysis of time series data is common in nutrition and metabolism research for quantifying the physiological responses to various stimuli. The reduction of many data from a time series into a summary statistic(s) can help quantify and communicate the overall response in a more straightforward way and in line with a specific hypothesis. Nevertheless, many summary statistics have been selected by various researchers, and some approaches are still complex. The time-intensive nature of such calculations can be a burden for especially large data sets and may, therefore, introduce computational errors, which are difficult to recognize and correct. In this short commentary, the authors introduce a newly developed tool that automates many of the processes commonly used by researchers for discrete time series analysis, with particular emphasis on how the tool may be implemented within nutrition and exercise science research.
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Bu araştırmanın amacı, kahvaltının egzersiz performansı üzerindeki etkilerini incelemektir. Bu doğrultuda vücudun uzun süre açlık ve tokluk durumlarındaki fizyolojik süreçleri detaylı olarak incelenmiştir. Araştırma, literatür taraması ve içerik analiz yöntemi kullanılarak yapılan derleme türü bir çalışmadır. Çalışmaya ait literatür veriler konuya ışık tutabilecek akademik yayınlar ve nitelikli kitaplardan elde edilmiştir. Çalışmaya dahil edilen literatür veriler ışığında kilo kontrol amaçlı egzersiz yapılan durumlarda aç karnına egzersiz yapmak, yağ oksidasyonunu arttırırken daha etkili ve hızlı kilo verilmesine destek olmaktadır. Ancak kas kütlesi kazanmak veya atletik performansı geliştirmek için antrenman yapıldığında, antrenmandan önce karbonhidrat tüketmek performansın korunmasına yardımcı olmaktadır. Aç karnına spor yapmak antrenman sırasında baş dönmesi, kan şekeri düşüklüğü veya aç hissetmeye neden oluyorsa, antrenmandan önce beslenmek doğru bir tercih olmaktadır. Yapılacak kahvaltı veya belli bir seviyedeki atıştırmalık bu olumsuzlukların giderilmesinde etkili olabilir. Kahvaltıyı atlamanın, günlük enerji alımını azaltmanın etkili bir yolu olabileceği düşünülürken o günün ilerleyen saatlerinde, öğle yemeğini tükettikten sonra bile egzersiz performansının bozulabileceği belirtilmektedir. Bu doğrultuda amaca yönelik olarak yapılacak doğru kahvaltı planlaması ister kilo kontrol amaçlı olsun ister performans amaçlı olsun büyük önem taşımaktadır. Anahtar Kelimeler: Kahvaltı, egzersiz, performans EFFECT OF BREAKFAST ON EXERCİSE PERFORMANCE ABSTRACT The aim of this research was to examine the effects of breakfast on exercise performance. In this direction, the physiological processes of the body in long-term hunger and satiety conditions were examined in detail. The research is a compilation type study using literature review and content analysis method. The literature data of the study were obtained from academic publications and qualified books that could shed light on the subject. In the light of the literature data included in the study, exercising on an empty stomach in cases where exercise for weight control purposes increases fat oxidation and supports more effective and faster weight loss. But when training to gain muscle mass or improve athletic performance, consuming carbohydrates before training helps maintain performance. If doing sports on an empty stomach causes dizziness, low blood sugar or feeling hungry during training, it is the right choice to eat before training. Breakfast or a snack at a certain level can be effective in eliminating these negativities. While it is thought that skipping breakfast can be an effective way to reduce daily energy intake, it is stated that exercise performance may deteriorate later in the day, even after consuming lunch. In this direction, the right breakfast planning to be done for the purpose, whether it is for weight control or performance purposes, is of great importance.
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Objective: To determine the acute effect of fasted and fed exercise on energy intake, energy expenditure, subjective hunger and gastrointestinal hormone release. Methods: CENTRAL, Embase, MEDLINE, PsycInfo, PubMed, Scopus and Web of Science databases were searched to identify randomised, crossover studies in healthy individuals that compared the following interventions: (i) fasted exercise with a standardised post-exercise meal [FastEx + Meal], (ii) fasted exercise without a standardised post-exercise meal [FastEx + NoMeal], (iii) fed exercise with a standardised post-exercise meal [FedEx + Meal], (iv) fed exercise without a standardised post-exercise meal [FedEx + NoMeal]. Studies must have measured ad libitum meal energy intake, within-lab energy intake, 24-h energy intake, energy expenditure, subjective hunger, acyl-ghrelin, peptide YY, and/or glucagon-like peptide 1. Random-effect network meta-analyses were performed for outcomes containing ≥5 studies. Results: 17 published articles (23 studies) were identified. Ad libitum meal energy intake was significantly lower during FedEx + Meal compared to FedEx + NoMeal (MD: -489 kJ; 95% CI, -898 to -80 kJ; P = 0.019). Within-lab energy intake was significantly lower during FastEx + NoMeal compared to FedEx + NoMeal (MD: -1326 kJ; 95% CI, -2102 to -550 kJ; P = 0.001). Similarly, 24-h energy intake following FastEx + NoMeal was significantly lower than FedEx + NoMeal (MD: -2095 kJ; 95% CI, -3910 kJ to -280 kJ; P = 0.024). Energy expenditure was however significantly lower during FastEx + NoMeal compared to FedEx+NoMeal (MD: -0.67 kJ/min; 95% CI, -1.10 to -0.23 kJ/min; P = 0.003). Subjective hunger was significantly higher during FastEx + Meal (MD: 13 mm; 95% CI, 5-21 mm; P = 0.001) and FastEx + NoMeal (MD: 23 mm; 95% CI, 16-30 mm; P < 0.001) compared to FedEx + NoMeal. Conclusion: FastEx + NoMeal appears to be the most effective strategy to produce a short-term decrease in energy intake, but also results in increased hunger and lowered energy expenditure. Concerns regarding experimental design however lower the confidence in these findings, necessitating future research to rectify these issues when investigating exercise meal timing and energy balance. Prospero registration number: CRD42020208041. Key points: Fed exercise with a standardised post-exercise meal resulted in the lowest energy intake at the ad libitum meal served following exercise completion. Fasted exercise without a standardised post-exercise meal resulted in the lowest within-lab and 24-h energy intake, but also produced the lowest energy expenditure and highest hunger. Methodological issues lower the confidence in these findings and necessitate future work to address identified problems.
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Abstract Aim: In this study the effects of a single training session of overweight men before and after a meal on serum acetylated ghrelin levels, daily energy intake and the exercise energy expenditure were compared. Method: In this semi experimental study, 30 overweight men (Mean and SD age of 25.2±3.54 years, BMI 27.96±3.64 kg/m2 , weight 83.2±5.8 kg) were randomized into three groups (n = 10) including before lunch training, post lunch training and control. Experimental groups performed eight weeks, three sessions/wk of aerobic training sessions, consisted of 25 to 40 min of treadmill running and/or cycling at maximal fat oxidation intensity, either an hour prior to or two hours after a meal. Exercise energy expenditure, daily caloric intake and fasting serum acylated ghrelin levels in response to a single exercise session were measured as data in both pre and post-test occasions. Results: A single training session either pre or post lunch meal increases serum acylated ghrelin level (P≤ 0/001), exercise energy expenditure (P≤ 0/001) and daily caloric intake (P≤ 0/001); indicating a compensatory energy intake which lowers the expected exercise-induced weight loss. However, pre meal exercise leads to more remarkable increases in exercise energy cost (P≤ 0/001) concomitant with an elevated fasting serum acylated ghrelin levels (P≤ 0/001). Conclusion: If appetite suppression is the only goal for exercise, it seems that exercise training should be performed after meals, and if maximizing each session’s energy cost is the case, it is better to practice before meals. Keywords: Obesity, Energy Intake, Energy Expenditure, Exercise, Meal
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Background Elevated glucose and insulin levels are major risk factors in the development of cardiometabolic disease. Aerobic exercise is widely recommended to improve glycaemic control, yet its acute effect on glycaemia and glucoregulatory hormones has not been systematically reviewed and analysed in healthy adults. Objective To determine the effect of a single bout of continuous aerobic exercise on circulating glucose, insulin, and glucagon concentrations in healthy adults. Methods CENTRAL, CINAHL, Embase, Global Health, HMIC, Medline, PubMed, PsycINFO, ScienceDirect, Scopus and Web of Science databases were searched from inception to May 2020. Papers were included if they reported a randomised, crossover study measuring glucose and/or insulin and/or glucagon concentrations before and immediately after a single bout of continuous aerobic exercise (≥ 30 min) compared to a time-matched, resting control arm in healthy adults. The risk of bias and quality of evidence were assessed using the Cochrane Risk of Bias Tool and GRADE approach, respectively. Random-effects meta-analyses were performed for glucose, insulin, and glucagon. Sub-group meta-analyses and meta-regression were performed for categorical (metabolic state [postprandial or fasted], exercise mode [cycle ergometer or treadmill]) and continuous (age, body mass index, % males, maximal aerobic capacity, exercise duration, exercise intensity) covariates, respectively. Results 42 papers (51 studies) were considered eligible: glucose (45 studies, 391 participants), insulin (38 studies, 377 participants) and glucagon (5 studies, 47 participants). Acute aerobic exercise had no significant effect on glucose concentrations (mean difference: − 0.05 mmol/L; 95% CI, − 0.22 to 0.13 mmol/L; P = 0.589; I²: 91.08%, large heterogeneity; moderate-quality evidence). Acute aerobic exercise significantly decreased insulin concentrations (mean difference: − 18.07 pmol/L; 95% CI, − 30.47 to − 5.66 pmol/L; P = 0.004; I²: 95.39%, large heterogeneity; moderate-quality evidence) and significantly increased glucagon concentrations (mean difference: 24.60 ng/L; 95% CI, 16.25 to 32.95 ng/L; P < 0.001; I²: 79.36%, large heterogeneity; moderate-quality evidence). Sub-group meta-analyses identified that metabolic state modified glucose and insulin responses, in which aerobic exercise significantly decreased glucose (mean difference: − 0.27 mmol/L; 95% CI, − 0.55 to − 0.00 mmol/L; P = 0.049; I²: 89.72%, large heterogeneity) and insulin (mean difference: − 42.63 pmol/L; 95% CI, − 66.18 to − 19.09 pmol/L; P < 0.001; I²: 81.29%, large heterogeneity) concentrations in the postprandial but not fasted state. Meta-regression revealed that the glucose concentrations were also moderated by exercise duration and maximal aerobic capacity. Conclusions Acute aerobic exercise performed in the postprandial state decreases glucose and insulin concentrations in healthy adults. Acute aerobic exercise also increases glucagon concentrations irrespective of metabolic state. Therefore, aerobic exercise undertaken in the postprandial state is an effective strategy to improve acute glycaemic control in healthy adults, supporting the role of aerobic exercise in reducing cardiometabolic disease incidence. PROSPERO registration number CRD42020191345.
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We investigated the relationship between mechanical and energy cost of transport and body mass in running humans. Ten severely obese (body mass ranging from 108.5 to 172.0 kg) and 15 normal-weighted (52.0-89.0 kg) boys and men, aged 16.0-45.8 years, participated in this study. The rate of O(2) consumption was measured and the subjects were filmed with four cameras for kinematic analysis, while running on a treadmill at 8 km h(-1). Mass specific energy cost (C (r)) and external mechanical work (W (ext)) per unit distance were calculated and expressed in joules per kilogram per meter, efficiency (η) was then calculated as W (ext) × C (r) (-1) × 100. Both mass-specific C (r) and W (ext) were found to be independent of body mass (M) (C (r) = 0.002 M + 3.729, n = 25, R (2) = 0.05; W (ext) = -0.001 M + 1.963, n = 25, R (2) = 0.01). It necessarily follows that the efficiency is also independent of M (η = -0.062 M + 53.3298, n = 25, R (2) = 0.05). The results strongly suggest that the elastic tissues of obese subjects can adapt (e.g., thickening) to the increased mass of the body thus maintaining their ability to store elastic energy, at least at 8 km h(-1) speed, at the same level as the normal-weighted subjects.
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This study investigated the effect of fasted and postprandial exercise on appetite, energy intake and resting metabolic responses. Twelve healthy males (mean±SD: age 23±3 years, body mass index 22.9±2.1 kg m(-2), maximum oxygen uptake 57.5±9.7 mL kg(-1) min(-1)) performed three 10 h experimental trials (control, fasted exercise and postprandial exercise) in a Latin Square design. Trials commenced at 8 am after an overnight fast. Sixty min of treadmill running at ∼70% of maximum oxygen uptake was performed at 0-1 h in the fasted exercise trial and 4-5 h in the postprandial exercise trial. A standardised breakfast was provided at 1.5 h and ad libitum buffet meals at 5.5 and 9.5 h. Appetite ratings and resting expired air samples were collected throughout each trial. Postprandial exercise suppressed appetite to a greater extent than fasted exercise. Ad libitum energy intake was not different between trials, resulting in a negative energy balance in exercise trials relative to control after accounting for differences in energy expenditure (control: 9774±2694 kJ; fasted exercise: 6481±2318 kJ; postprandial exercise: 6017±3050 kJ). These findings suggest that 60 min treadmill running induces a negative daily energy balance relative to a sedentary day but is no more effective when performed before or after breakfast.
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Splanchnic hypoperfusion is common in various pathophysiological conditions and often considered to lead to gut dysfunction. While it is known that physiological situations such as physical exercise also result in splanchnic hypoperfusion, the consequences of flow redistribution at the expense of abdominal organs remained to be determined. This study focuses on the effects of splanchnic hypoperfusion on the gut, and the relationship between hypoperfusion, intestinal injury and permeability during physical exercise in healthy men. Healthy men cycled for 60 minutes at 70% of maximum workload capacity. Splanchnic hypoperfusion was assessed using gastric tonometry. Blood, sampled every 10 minutes, was analyzed for enterocyte damage parameters (intestinal fatty acid binding protein (I-FABP) and ileal bile acid binding protein (I-BABP)). Changes in intestinal permeability were assessed using sugar probes. Furthermore, liver and renal parameters were assessed. Splanchnic perfusion rapidly decreased during exercise, reflected by increased gap(g-a)pCO(2) from -0.85±0.15 to 0.85±0.42 kPa (p<0.001). Hypoperfusion increased plasma I-FABP (615±118 vs. 309±46 pg/ml, p<0.001) and I-BABP (14.30±2.20 vs. 5.06±1.27 ng/ml, p<0.001), and hypoperfusion correlated significantly with this small intestinal damage (r(S) = 0.59; p<0.001). Last of all, plasma analysis revealed an increase in small intestinal permeability after exercise (p<0.001), which correlated with intestinal injury (r(S) = 0.50; p<0.001). Liver parameters, but not renal parameters were elevated. Exercise-induced splanchnic hypoperfusion results in quantifiable small intestinal injury. Importantly, the extent of intestinal injury correlates with transiently increased small intestinal permeability, indicating gut barrier dysfunction in healthy individuals. These physiological observations increase our knowledge of splanchnic hypoperfusion sequelae, and may help to understand and prevent these phenomena in patients.
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Position Statement: Admittedly, research to date examining the physiological effects of meal frequency in humans is somewhat limited. More specifically, data that has specifically examined the impact of meal frequency on body composition, training adaptations, and performance in physically active individuals and athletes is scant. Until more research is available in the physically active and athletic populations, definitive conclusions cannot be made. However, within the confines of the current scientific literature, we assert that: 1. Increasing meal frequency does not appear to favorably change body composition in sedentary populations. 2. If protein levels are adequate, increasing meal frequency during periods of hypoenergetic dieting may preserve lean body mass in athletic populations. 3. Increased meal frequency appears to have a positive effect on various blood markers of health, particularly LDL cholesterol, total cholesterol, and insulin. 4. Increased meal frequency does not appear to significantly enhance diet induced thermogenesis, total energy expenditure or resting metabolic rate. 5. Increasing meal frequency appears to help decrease hunger and improve appetite control. The following literature review has been prepared by the authors in support of the aforementioned position statement.
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Investigations of the impact of physical activity on appetite control have the potential to throw light on the understanding of energy balance and therefore, upon body weight regulation and the development of obesity. Given the complexity of the landscape influencing weight regulation,research strategies should reflect this complexity. We have developed a research approach based on the concept of the psychobiological system (multi-level measurement and analysis) and an experimental platform that respects the operations of an adaptive regulating biological system. It is important that both sides of the energy balance equation (activity and diet) receive similar detailed levels of analysis. The experimental platform uses realistic and fully supervised levels of physical activity, medium-term (not acute) interventions, measurement of body composition, energy metabolism (indirect calorimetry), satiety physiology(gut peptides), homeostatic and hedonic processes of appetite control, non-exercise activity, obese adult participants and both genders. This research approach has shown that the impact of physical activity on appetite control is characterised by large individual differences. Changes in body composition, waist circumference and health benefits are more meaningful than changes in weight. Further, we are realising that the acute effects do not predict what will happen in the longer term. The psychobiological systems approach offers a strategy for simultaneously investigating biological and behavioural processes relevant to understanding obese people and how obesity can be managed. This experimental platform provides opportunities for industry to examine the impact of foods under scientifically controlled conditions relevant to the real world.
Article
Background:Whey proteins have insulinotropic effects and reduce the postprandial glycemia in healthy subjects. The mechanism is not known, but insulinogenic amino acids and the incretin hormones seem to be involved. Objective:The aim was to evaluate whether supplementation of meals with a high glycemic index (GI) with whey proteins may increase insulin secretion and improve blood glucose control in type 2 diabetic subjects. Design:Fourteen diet-treated subjects with type 2 diabetes were served a high-GI breakfast (white bread) and subsequent high-GI lunch (mashed potatoes with meatballs). The breakfast and lunch meals were supplemented with whey on one day; whey was exchanged for lean ham and lactose on another day. Venous blood samples were drawn before and during 4 h after breakfast and 3 h after lunch for the measurement of blood glucose, serum insulin, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide 1 (GLP-1). Results:The insulin responses were higher after both breakfast (31%) and lunch (57%) when whey was included in the meal than when whey was not included. After lunch, the blood glucose response was significantly reduced [−21%; 120 min area under the curve (AUC)] after whey ingestion. Postprandial GIP responses were higher after whey ingestion, whereas no differences were found in GLP-1 between the reference and test meals. Conclusions:It can be concluded that the addition of whey to meals with rapidly digested and absorbed carbohydrates stimulates insulin release and reduces postprandial blood glucose excursion after a lunch meal consisting of mashed potatoes and meatballs in type 2 diabetic subjects.
Article
This study assessed the effect of exercise timing relative to meal consumption on appetite and its hormonal regulators (i.e., PYY3–36, ghrelin and leptin) in moderately active young men. Twelve men performed three trials in a random order: (1) meal consumption, (2) exercise 2 h after a meal, (3) exercise 1 h before a meal. The test meal provided 16.5 kcal kg−1 with 70% fat, 26% carbohydrate and 4% protein. Exercise was performed at a work rate eliciting 60% of VO2max for 50 min. Hunger ratings and plasma leptin concentrations were measured at baseline and hours 1, 3, 5, and 7 post-meal, and plasma concentrations of ghrelin and PYY3–36 were measured at baseline and 1, 3, and 7 h after meal consumption. Exercise performed 2 h after meal consumption extended the appetite suppressing effect of food intake. Furthermore, plasma PYY3–36 concentration tended to be elevated by exercise after meal consumption. Exercise prior to food intake decreased appetite and increased plasma ghrelin concentrations. No response to timing of exercise relative to food intake on plasma leptin concentration was detected. These data indicated the timing of exercise to meal consumption may influence appetite and its hormonal regulators. Post-meal exercise may extend the suppressive effects of meal consumption on appetite.
Article
Paired frequently sampled intravenous glucose tolerance tests (FSIGT) were performed on five highly trained athletes within 2 hours of completing a 6-day ultramarathon run (E) and after 2 weeks of complete rest (R). Severe exercise increased free fatty acid (FFA) levels (E 1.2 ± 0.16 v 0.42 ± 0.07 mmol/L, P < .01) and norepinephrine levels (E 573 ± 141 v 224 ± 33 pg/mL, P < .01), with only moderate reductions in glucose tolerance (glucose disappearance [Kg] E 1.06 ± 0.2 v R 1.7 ± 0.3 min−1 × 102, P < .05). The minimal model analysis of FSIGT data using the method of Bergman et al (Endocr Rev 6:45–86, 1985) showed a reduced second-phase insulin secretion ([Φ2] E 5.2 ± 1.3 v 13 ± 2.2 μU/mL · min−2 per mg/dL, P < .05) and glucose disposition index ([SI × Φ2] E 33.8 ± 10 v 73.9 ± 11 mg−1 · dL · min−3 × 104, P < .02). Insulin sensitivity (SI) and glucose-mediated glucose disposal (SG) were unchanged (SI E 6.9 ± 1.0 v 6.0 ± 0.6 min−1 per μU/mL × 104; SG E 1.8 ± 0.6 v 1.4 ± 0.3 min−1 × 102). Reduced glucose tolerance after prolonged extreme physical exercise was accompanied by reduced Φ2 and not by alterations of SI or SG, despite the marked increase of FFA levels. Elevated norepinephrine levels, reflecting activation of the sympathetic noradrenergic system, was also associated with the reduction in Kg. The reduction in Φ2 would promote mobilization of FFA, the predominant metabolic substrate in these endurance events.
Article
The effects of breakfast consumption on energy intake and the responses to foods consumed later in the day remain unclear. Twelve men of healthy body weight who reported regularly consuming breakfast (mean ± SD age 23.4 ± 7.3 y; BMI 23.5 ± 1.7 kg/m(2)) completed 2 trials using a randomized crossover design. Participants were provided with a 1050-kJ liquid preload 150 min after consuming a standardized breakfast (B) (10% daily energy requirement and 14, 14, and 72% energy from protein, fat, and carbohydrate, respectively), or no breakfast (NB). Blood glucose and serum insulin responses to the preload (area under the curve) were higher in the NB condition (P < 0.05). Plasma FFA responses to the preload were higher in the NB condition (P < 0.01). Plasma glucagon-like peptide 1 (P < 0.01) and plasma peptide Y (P < 0.05) responses were higher after the preload in the B condition. Desire to eat, fullness, and hunger ratings collected immediately prior to consuming the preload were all different from the fasting values in the NB condition (P < 0.05). Thus, immediately prior to consuming the preload, the fullness rating was lower and hunger and desire to eat ratings were higher in the NB condition (P < 0.05). Energy intake at the lunchtime test meal was ~17% lower in the B condition (P < 0.01). In conclusion, missing breakfast causes metabolic and hormonal differences in the responses to foods consumed later in the morning as well as differences in subjective appetite and a compensatory increase in energy intake.