EFFECTS OF AEROBIC EXERCISE PERFORMED IN FASTED VERSUS FED STATE ON FAT AND CARBOHYDRATE METABOLISM IN ADULTS: A SYSTEMATIC REVIEW AND META-ANALYSIS

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DOI: 10.1017/S0007114516003160
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Abstract
This study aimed to verify the effect of aerobic exercise performed in the fasted versus fed states on fat and carbohydrate metabolism in adults. Searches were conducted in March 2015, and updated in July 2016, using PubMed®, Scopus, and Cochrane databases (terms: ‘fasting’, ‘exercise’, ‘aerobic exercise’, ‘substrate’, ‘energy metabolism’, ‘fat’, ‘glucose’, ‘insulin’, and ‘adult’) and references from selected studies. Trials that compared the metabolic effects of aerobic exercise (duration ≤120 minutes) performed in the fasted versus fed states in adults, were accepted. The outcomes evaluated were fat oxidation during exercise, and the plasma concentrations of insulin, glucose, and non-esterified fatty acids before and immediately after exercise. Two independent reviewers extracted the data (A.F.V. and L.C.). The results were presented as weighted mean differences between treatments, with 95% confidence intervals. Of 10405 articles identified, 30 studies—with a total of 273 participants—were included. There was a significant increase in fat oxidation during exercise performed in the fasted, compared with fed, state (-3.08 g; 95% CI: -5.38, -0.79; I²: 39.1%). The weighted mean difference of non-esterified fatty acid concentrations was not significantly different between states (0.00 mmol/L; CI 95%: -0.07, 0.08; I²: 72.7%). However, the weighted mean differences of glucose (0.78 mmol/L; CI 95%: 0.43, 1.14; I²: 90.8%) and insulin concentration (104.5 pmol/L; CI 95%: 70.8, 138.2; I²: 94,5%) were significantly higher for exercise performed in the fed state. We conclude that aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.
Effects of aerobic exercise performed in fasted
v.
fed state on fat and
carbohydrate metabolism in adults: a systematic review and meta-analysis
Alexandra Ferreira Vieira
2
*, Rochelle Rocha Costa
1,2
, Rodrigo Cauduro Oliveira Macedo
1,3
,
Leandro Coconcelli
1,2
and Luiz Fernando Martins Kruel
1,2
1
Physical Education, Physiotherapy and Dance School, Federal University of Rio Grande do Sul, 750, Felizardo Street,
90690-200 Porto Alegre, Brazil
2
Research Group on Water and Land Activities, Federal University of Rio Grande do Sul, 750, Felizardo Street,
90690-200 Porto Alegre, Brazil
3
Research Group on Exercise Physiology and Biochemistry, Federal University of Rio Grande do Sul, 750, Felizardo Street,
90690-200 Porto Alegre, Brazil
(Submitted 7 March 2016 Final revision received 29 July 2016 Accepted 3 August 2016)
Abstract
This study aimed to verify the effect of aerobic exercise performed in the fasted v. fed states on fat and carbohydrate metabolism in adults.
Searches were conducted in March 2015, and updated in July 2016, using PubMed
®
, Scopus and Cochrane databases (terms: fasting,
exercise,aerobic exercise,substrate,energy metabolism,fat,glucose,insulinand adult) and references from selected studies. Trials
that compared the metabolic effects of aerobic exercise (duration 120 min) performed in the fasted v. fed states in adults were accepted. The
outcomes evaluated were fat oxidation during exercise and the plasma concentrations of insulin, glucose and NEFA before and immediately
after exercise; two independent reviewers extracted the data (A. F. V. and L. C.). The results were presented as weighted mean differences
between treatments, with 95 % CI. Of 10 405 articles identied, twenty-seven studies with a total of 273 participants were included. There
was a signicant increase in fat oxidation during exercise performed in the fasted, compared with fed, state (3·08 g; 95 % CI 5·38, 0·79; I
2
39·1 %). The weighted mean difference of NEFA concentrations was not signicantly different between states (0·00 mmol/l; 95 % CI 0·07,
0·08; I
2
72·7 %). However, the weighted mean differences of glucose (0·78 mmol/l; 95 % CI 0·43, 1·14; I
2
90·8 %) and insulin concentrations
(104·5 pmol/l; 95 % CI 70·8, 138·2; I
2
94·5 %) were signicantly higher for exercise performed in the fed state. We conclude that aerobic
exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.
Key words: Fasting: Exercise: Energy metabolism: Reviews
Fasting is characterised by the absence of food and/or energy
beverage intake for a period of time, which may last from several
hours to a few weeks
(1,2)
. However, most people fast for 812 h
daily the overnight fastingperiod
(2)
. During this period, NEFA,
ketone bodies and glucose derived from liver glycogen and
gluconeogenesis are the predominant energy sources
(3)
.
During exercise, NEFA also make a considerable contribution
to energy metabolism owing to the increased availability of
these substrates in the plasma. This is caused by increased
adrenaline levels and decreased insulin concentrations in the
blood
(4)
. Fasting promotes low levels of insulin and hepatic
glycogen
(2)
. Thus, when aerobic exercise is performed under
these conditions, an increase in the utilisation of fat as an
energy substrate is observed, when compared with exercise
performed in the fed state
(5,6)
. The decrease in fat oxidation
during exercise in the fed state can be mainly attributed to
higher insulin concentrations caused by a meal, which may
inhibit the breakdown of intramuscular TAG (IMTG) and
reduce the availability of NEFA for oxidation
(7,8)
.
Several studies have indicated that regular exercise promotes
benecial effects in terms of health and body composition
(911)
,
including an improvement in insulin sensitivity and main-
tenance and reduction of body weight and body fat. It has been
suggested that exercise enhances fat oxidation and that
this adaptation may be associated with improved insulin
sensitivity
(12)
. Furthermore, higher fat oxidation capacity during
exercise seems to be related to a decrease in the number of
metabolic risk factors
(13)
. Venables & Jeukendrup
(14)
demon-
strated that participating in a training programme for 4 weeks,
with continuous aerobic exercise programmed for the max-
imum contribution of fat as the energy substrate during each
session, can further increase fat oxidation. This higher oxidation
was associated with improvements in insulin sensitivity in
obese men. In healthy, young men, the maximal fat oxidation
Abbreviation: IMTG; intramuscular TAG.
*Corresponding author: A. F. Vieira, fax +55 51 3308 5820, email alexandrafvieira@hotmail.com
British Journal of Nutrition, page 1 of 12 doi:10.1017/S0007114516003160
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during exercise was positively associated with insulin sensitivity
and 24-h fat oxidation
(15)
. Studies have demonstrated that
exercise performed in the fasted state can increase the rate of fat
oxidation at rest from 9
(16)
to 24 h
(1719)
after exercise when
compared with the same exercise performed after a meal. This
higher utilisation of fat as an energy source at rest may promote
reduction in body fat.
On the basis of these data, aerobic exercise performed in the
fasted state has been considered a strategy to increase fat
oxidation during exercise and, chronically, to promote adapta-
tions that may be benecial to health. However, although most
studies reported higher fat oxidation under these conditions
compared with a carbohydrate-fed state, it is not clear whether
the stimulation of lipolytic activity and/or decreased
re-esterication of NEFA that occur during the fasted state
(20)
result in a signicantly increased use of fat as an energy substrate
during exercise. This systematic review with meta-analysis aimed
to verify the effect of aerobic exercise performed during fasted v.
fed states on fat and carbohydrate metabolism in adults.
Methods
Eligibility criteria
This review considered clinical trials (parallel and randomised
cross-over designs) evaluating the effect of performing an
aerobic exercise intervention of no >120 min duration (or data
at 120 min for those interventions with longer durations) in
a fasted state among adults aged 1959 years. These interven-
tions had to be compared with the same exercise performed in
the fed state (prior consumption of meals containing at least
25 g of carbohydrates)
(21)
. Included studies evaluated the
following outcome measures: fat oxidation during exercise,
considered the primary end point; and serum concentrations of
NEFA, glucose and insulin immediately before and after the
exercise session; the absolute weighted mean differences of
these concentrations were considered the secondary end
points. Studies that evaluated these acute responses to aerobic
exercise were included; trials that did not present acute
outcome data were excluded. In the case of trials with several
publications (or sub-studies), the study was included only once.
Search strategy
The electronic databases MEDLINE
®
(via PubMed
®
), Scopus
and Cochrane were used. In addition, manual searches were
conducted of references of studies identied for inclusion. The
search was conducted in March 2015 and updated in July 2016.
The terms fasting,exercise,aerobic exercise,substrate,
energy metabolism,fat,glucose,insulinand adultas well
as related entry terms were used. The searches were limited
to articles published in English, Portuguese and Spanish
languages. The search strategy used in the PubMed
®
database is
available as the online Supplementary Material. Details of other
strategies may be obtained upon request. This systematic
review and meta-analysis was prepared and is presented in
accordance with Preferred Reporting Items for Systematic
Reviews and Meta-Analysesguidelines
(22,23)
.
Selection of studies
Selection of studies for review was performed independently and
duplicated, without restriction on the date of publication. First,
the titles and abstracts of all articles identied by the search
strategy were evaluated for inclusion independently by two
researchers (A. F. V. and L. C.), in duplicate form. Whenever the
abstract did not provide sufcient information about inclusion
and exclusion criteria, the full article was evaluated. Second, the
same reviewers independently evaluated the full articles of those
identied as appropriate from the abstract screening process, and
made their selection according to eligibility criteria. Disagree-
ments between reviewers were resolved by consensus, and in
the case of continuing disagreement the evaluation was made by
a third reviewer (R. R. C.). To avoid possible double counting of
participants included in more than one report by the same
authors/working groups, the periods of recruitment of partici-
pants and areas of recruitment were evaluated, and authors were
contacted for clarication where necessary.
Data extraction
Data extraction was performed by two reviewers (A. F. V. and
L. C.) independently concerning methodological characteristics,
interventions and outcomes of the studies using a standardised
form. As in the selection stage, disagreements were resolved
by consensus or by a third reviewer (R. R. C.). The extracted
data included average age, BMI, sex and training status of
participants; exercise duration and intensity; time between dietary
intake and the start of exercise; amount of carbohydrate
consumed in the pre-exercise meal; and the end points analysed.
Iftherequireddatawerenotfoundinthepublishedreport,the
corresponding author was contactedtoprovidemissingdataand,
in the absence of responses or data extraction alternatives, the
study or missing end point was excluded from the review. Data
presented only graphically, and for which more detail was not
provided despite a request to the corresponding authors, were
extracted using DigitizeItsoftware. Where it was not possible to
extract means or standard deviations from graphs at the required
points, the variable was excluded from the analysis.
In this phase, studies that included diabetic participants, or those
in which carbohydrates were provided during exercise as part of
the study protocol, were excluded to avoid possible bias in the
results. The primary end point we assessed was the total absolute
average fat oxidation during exercise. Secondary end points were
theweightedmeandifferenceininsulin,glucoseandNEFAcon-
centrations. Weighted mean differences were calculated from
values taken immediately before and during the last minute of
exercise for studies lasting 120 min. For studies of longer dura-
tion, the time 120 minwas considered the last minute of exercise.
In studies where the total absolute average fat oxidation during
exercise was not presented in the published article, a request was
submitted to the authors, and if means for VO
2
and carbon
dioxide production values were provided these were applied to
the formula determined by Péronnet & Massicotte
(24)
in order to
determine the fat oxidation rate. The units of measurements
used in this review were grams for fat oxidation, mmol/l for
concentrations of NEFA and glucose, and pmol/l for insulin
2 A. F. Vieira et al.
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concentrations. Study data not presented in these units were
converted. For instance, where fat oxidation was presented using
an energy value (kJ/kcal), these averages were divided by 40·79 kJ
(9·75 kcal) in order to obtain the value in grams
(25)
.Ifthesedata
were not provided by authors, or if it was not possible to calculate
the total oxidised absolute averageduringexercise,thevariableor
the study was excluded. Studies with two or more comparison
groups with the same population were included with only one
comparator, which was selected according to the time between
dietary intake and exercise and/or the nutritional characteristics of
meals consumed that most closely resembled the other studies
being reviewed, in an effort to standardise results. For studies with
two or more intervention groups, a single group was also inclu-
ded, selected according to characteristics similar to other studies.
Evaluation of risk of bias
The assessment of the methodological quality of included
studies was performed according to criteria proposed by
Cochrane
(26)
: appropriate use of randomisation sequences,
allocation concealment, blinding of participants and/or thera-
pists, blinding of assessors to outcomes, and description of
losses and exclusions. When these processes had been descri-
bed in the published document, it was considered that criteria
had been met and these studies were classied as being at low
riskof bias and, in opposition, as high risk. Studies that did not
report these data were classied as unclear risk. Descriptions
of losses and exclusions were considered low riskwhen the
number of participants evaluated were presented in the legends
of charts and graphs. Quality evaluation was performed
independently by two reviewers (A. F. V. and L. C.).
Data analysis
Results are presented as weighted mean differences for absolute
values between treatments with 95 % CI. The standard deviation
of mean difference values not provided by studies was imputed
according to the equation proposed by Higgins et al.
(27)
.
Statistical heterogeneity of treatment effects between studies
was evaluated by CochransQtest and I
2
inconsistency test;
values above 50 % indicated high heterogeneity
(28)
. In case of
low heterogeneity, the xed effect model was used to pool
study results for the outcomes. When signicant heterogeneity
was observed (I
2
>50 %), the random effects model was
applied. Meta-analyses comprised comparisons of fat oxidation
during aerobic exercise performed in the fasted v. fed state and
the changes in concentrations (expressed using weighted mean
differences) of glucose, NEFA and insulin from immediately
before exercise to the last minute of exercise (post-exercise).
Values of α0·05 were considered statistically signicant.
For variables with high heterogeneity, sensitivity analyses
were performed according to the following criteria: exercise
time, exercise intensity, sex of participants, BMI of participants,
training level of participants, pre-exercise values for each vari-
able, time between dietary intake and the start of exercise, and
amount of carbohydrate consumed in the pre-exercise meal.
Furthermore, publication bias was assessed using funnel plots
for each outcome (of each trials effect size against the standard
error). Funnel plot asymmetry was evaluated using Begg and
Egger tests
(29)
,andasignicant publication bias was considered
if P<0·10. The trim-and-ll computation was used to estimate
the effect of publication bias on the interpretation of results.
All analyses were performed using Comprehensive
Meta-Analysis version 2.0, except the risk of bias, which was
performed using Review Manager version 5.3 (Cochrane
Collaboration).
Results
Description of studies
Of the 10 405 studies identied from the database searches,
twenty-three met our inclusion criteria. An additional four studies
were included from a manual search of the reference lists of the
included studies, bringing the total number of articles included to
twenty-seven. Of these, three studies
(3032)
were included twice
because they had met eligibility criteria for two groups with
different populations, in which each population had a different
intervention group and control group: references Bergman &
Brooks, 1999aand Montain et al., 1991arelated to populations
comprised of trained men, Bergman & Brooks, 1999band
Montain et al., 1991brelated to populations comprised of
untrained men, and Isacco et al., 2012aand Isacco et al., 2012b
related to populations of women who did not and did use the
contraceptive pill, respectively. Thus, thirty comparisons were
used in this meta-analysis (Fig. 1). In total, 270 and 269 partici-
pants were included in the fasted and fed groups, respectively.
The majority of studies (80 %) analysed men, whereas 13·3%
analysed women, and 6·6 % analysed both sexes. Most samples
comprised physically active individuals (86·7 %), and exercise
sessions lasted an average of 73min. The meals were provided
30240min before the interventions and were composed of a
maximum of 215g of carbohydrates (Table 1).
In all, four studies were excluded from our analysis: one study
was unaccessible
(33)
, and the other three met all eligibility criteria,
but were not used because of the unavailability of results
(34)
,
or the presentation of averages
(19)
and standard deviations
(35)
graphically, with no clarication received from authors and no
possibility of data extraction using DigitizeItsoftware.
From some of the studies included, it was necessary to exclude
certain variables because absolute averages were not given for
example, the absolute average of fat oxidation during
exercise
(6,7,3638)
. Other variables were excluded as it was
impossible to extract values for standard deviation of insu-
lin
(3942)
,glucose
(40,41,43)
and NEFA
(32,40)
concentrations. These
data were all requested from authors but were not provided.
DigitizeItsoftware was used to extract the average relating to fat
oxidation from one study
(44)
, relating to NEFA concentrations
from fourteen studies
(6,7,37,38, 4143,4551)
, relating to glucose con-
centrations from sixteen studies
(6,7,32,3639,42,4552)
and relating to
insulin concentrations from thirteen studies
(6,7,37,38 ,43,4552)
.
Risk of bias
Of the included studies, 80 % showed adequate generation
of randomisation sequence, 6·6 % reported allocation
Exercise in fasted adults and fat oxidation 3
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concealment, 20 % had blinded participants and/or therapists,
6·6 % had blinded the assessors to the outcomes and 66·6%
described losses to follow-up and exclusions (Fig. 2 and 3).
Effects of interventions
Fat oxidation. Data on fat oxidation were available from eleven
studies
(30,31,3941,43,44,47,5052)
, with a total of 117 individuals
evaluated (Fig. 4). Aerobic exercise performed in the fasted
state was associated with a signicant increase in fat oxidation
during exercise when compared with the fed state (effect size:
3·53; 95 % CI 4·76, 2·30; I
2
39·1 %). Aerobic exercise
performed in the fasted state led to an increase in fat oxidation
of approximately 3·53 g, compared with execution of the same
exercise after consumption of meals containing carbohydrates.
However, the analysis of publication bias identied a signicant
bias (P=0·007), and thus the adjusted value of the effect size,
according to the Duval & Tweedies trim and ll test, resulted
in 3·08 g.
Given the inuence of exercise intensity on fat oxidation,
sensitivity analyses were performed to identify whether there
was an effect difference when stratied by two different
intensity ratings VO
2max
<70 % and VO
2max
70 %. Thus, even
though the meta-analysis did not demonstrate signicant het-
erogeneity (P=0·07), sensitivity analyses were performed:
<70 % VO
2max
(3·45 g; 95 % CI 2·19, 4·71; P<0·001; I
2
50 %) and
70 % VO
2max
(5·38 g; 95 % CI 0·45, 11·21; P=0·07; I
2
0 %).
Aerobic exercise of low-to-moderate intensity performed in the
fasted state induced a higher fat oxidation compared with a fed
state. On the other hand, there was no signicant difference
between fasted and fed states in relation to fat oxidation during
aerobic exercise of moderate-to-high intensity.
Sensitivity analyses were also performed for fat oxidation
taking the following into account: exercise time (60 min:
3·35 g; 95 % CI 2·07, 4·62; P<0·001; I
2
54 %; >60 min: 6·13 g;
95 % CI 1·37, 10·88; P=0·01; I
2
9 %); sex of participants (male:
6·39 g; 95 % CI 3·84, 8·94; P<0·001; I
2
0 %; female: 2·60 g;
95 % CI 1·19, 4·01; P=0·0003; I
2
0 %); BMI of participants
(<25 kg/m
2
:2·79 g; 95 % CI 1·42, 4·17; P<0·001; I
2
30 %);
training level of participants (physically active: 3·74 g; 95 % CI
1·97, 5·52; P<0·001; I
2
49 %; sedentary: 3·34 g; 95 % CI 1·62,
5·05; P=0·0001; I
2
23 %); time between consumption of meal
and the beginning of exercise (<100 min: 3·41 g; 95 % CI 1·68,
5·14; P=0·0001; I
2
57 %; >100 min: 3·66 g; 95 % CI 1·91, 5·41;
P<0·001; I
2
37 %); and quantity of carbohydrate consumed in
the pre-exercise meal (<100 g: 3·51 g; 95 % CI 1·84, 5·17;
P<0·001; I
2
34 %; 100 g: 3·56 g; 95 % CI 1·73, 5·39; P=0·0001;
I
2
53 %). Thereby, these results demonstrated no change in
the pattern already presented, of higher fat oxidation when
the exercise is performed in the fasted state, regardless of the
adopted criteria for the sensitivity analyses.
NEFA. Data on NEFA concentrations were available from
sixteen studies
(6,7,31,37,38,4143,4552)
, with a total of 144 indivi-
duals evaluated (Fig. 5). All but one of these studies used
the same sample populations for both interventions
(37)
. The
weighted mean difference of NEFA before and after exercise
10 405 articles identified through
database search
Identification
9857 articles after the removal of
duplicates
69 full-text articles assessed
for eligibility
27 articles included 3 studies with two different populations
4 studies selected based on analysis of the
references of included studies
46 exclusions after reading the full-text
4 did not study the target population
3 did not evaluate the interest variables
23 did not perform the intervention
10 did not have the adequate comparator
2 studies with multiple publications
4 studies without access to the results
9788 exclusions based on the title and/or
summary review
2073 did not study the target population
5020 did not perform the intervention
40 did not have the adequate comparator
56 did not evaluate the interest variables
2599 did not have the appropriate design
SelectionEligibilityInclusion
Fig. 1. Flow chart of the included studies.
4 A. F. Vieira et al.
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Tab le 1 . Characteristics of included studies
(Mean values and standard deviations)*
Age (years)
Exercise duration Time between meal Amount of carbohydrate
Studies Mean SD Sex/nTraining status (min) Exercise intensity and exercise (min) pre exercise meal (g)
Aziz et al.
(53)
27·37·2 Male/10 Physically active 60 65·0% VO
2max
180 to 240 126·7
Bergman & Brooks
(30)
25·14·8 Male/7 Physically active 90 60·0% VO
2peak
180 119·6
Bergman & Brooks
(30)
22·13·4 Male/7 Sedentary 120 40·0% VO
2peak
180 119·6
Bouhlel et al.
(54)
19·02·0 Male/9 Physically active 30 20·0, 30·0, 40·0, 50·0, 60·0% W
max
Does not mention Does not mention
Coyle et al.
(45)
25·05·0 Male/7 Physically active 105 70·0% VO
2max
240 141·8
Coyle et al.
(7)
22·04·9 Male/6 Physically active 40 50·0% VO
2max
60 and 10 96·6
Dohm et al.
(46)
28·73·9 Male/9 Physically active 90 or until exhaustion
(about 80)
70·075·0% VO
2max
120 to 240 47·0
Farah & Gill
(39)
28·110·7 Male/10 Sedentary 60 50·0% VO
2max
30 56·5
Gonzalez et al.
(47)
23·24·3 Male/12 Physically active 59 61·1% VO
2peak
120 66·6
Guéye et al.
(55)
22·51·7 Male/12 Physically active 60 75·0% HR
max
Does not mention Does not mention
Horowitz et al.
(6)
26·59·3 Male/6 Physically active 60 44·0% VO
2peak
60 60·0
Isacco et al.
(31)
22·93·6 Female/10 Sedentary 45 65·0% VO
2max
180 72·2
Isacco et al.
(31)
21·21·9 Female/11 Sedentary 45 65·0% VO
2max
180 73·4
Kirwan et al.
(48)
22·02·4 Male/6 Physically active Until exhaustion (120) 60·0% VO
2peak
45 75·0
Kirwan et al.
(49)
24·04·9 Female/6 Physically active Until exhaustion (120) 60·0% VO
2peak
45 75·0
Little et al.
(36)
23·33·8 Male/7 Physically active 90 (45) V
max
180 86·0
Little et al.
(50)
22·83·2 Male/13 Physically active 105 V
max
120 Does not mention (1·5 g/kg)
Massicotte et al.
(52)
24·8(SD 6·9) (fast)
22·1(
SD 5·8) (fed)
Male/5 Physically active 120 (60) 52·0% VO
2max
180 50·0
Maughan &
Gleeson
(40)
34·08·9 Male/5 Physically active Until exhaustion (90) 70·0% VO
2max
45 69·8
Montain et al.
(32)
Does not mention Male/9 Physically active 30 70·0% VO
2peak
120 131·6
Montain et al.
(32)
Does not mention Male/8 Physically active 30 70·0% VO
2peak
120 154·6
Paul et al.
(41)
24·93·4 Mixed/12 Physically active 90 60·0% VO
2peak
90 32·4
Ramos-Jiménez
et al.
(56)
22·53·7 Mixed/30 Physically active 8 to 15 98·0% HR
max
70 Does not mention
(60 % ETV meal)
Satabin et al.
(42)
25·217·7 Male/9 Physically active 110 60·0% VO
2max
60 100·0
Schabort et al.
(37)
26·07·9 Male/7 Physically active 105 70·0% VO
2max
180 100·0
Shin et al.
(38)
23·32·5 Male/8 Physically active 60 50·0% VO
2max
30 66·4
Whitley et al.
(43)
21·010·8 Male/8 Physically active 90 70·0% VO
2max
240 215·0
Willcutts et al.
(44)
23·72·4 Female/8 Physically active 30 (23) 62·0% VO
2max
90 109·3
Wu et al.
(51)
26·83·3 Male/9 Physically active 60 65·0% VO
2max
180 141·0
Ziogas & Thomas
(57)
27·43·8 Male/7 Physically active 60 60·0% VO
2max
180 111·5
VO
2peak
, peak VO
2
;W
max
, maximum power; HR
max
, maximum heart rate; V
max
, maximum velocity; ETV, energy total value.
* Exercise duration: total time of exercise duration evaluated in the study (time post exercise extracted).
Exercise in fasted adults and fat oxidation 5
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  • Article
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    In this study we investigated the acute effects of low-intensity exercise on the postprandial hormonal and metabolic milieu induced by breakfast consumption. Exercise began 100 min after the initiation of breakfast consumption and consisted in cycling at 40% VO2max for 20 min. Three different breakfasts were used to elicit the postprandial state: B1 = skimmed milk (125mL) and 30-g corn flakes; B2 = skimmed milk (220mL), 200-g apple, 30-g cocoa-cream-filled sponge cake; B3 = skimmed milk (125mL), 50-g bread, 150-g apple, and 15-g hazelnut and cocoa spread. Nineteen young healthy subjects (8M/11F; BMI 22.7±0.5 kg/m2; 31±0.7 yrs) underwent the three breakfasts, as well as an oral glucose load (50-g OGTT), under either resting or exercise conditions, in a randomized-crossover fashion. Blood glucose, insulinemia, ghrelinemia, lipidemia, and satiety were measured throughout the studies. In order to evaluate the metabolic effects of exercise, the changes that glucose, insulin, ghrelin, FFA exhibited in the interval 90-120 min were analyzed with a two-way repeated measures ANOVA (factor 1: type of oral test; factor 2: resting/exercise condition). No interaction between the two factors was found for any of the examined variables. Light exercise produced a modest, significant decrease in blood glucose levels (p=0.004) and a modest, significant increase in FFA levels (p=0.002) with respect to the resting condition. These findings suggest that short, mild exercise has beneficial effects on postprandial metabolism and this may have direct bearing on the issue of counteracting the epidemic rising of sedentary lifestyle of the general population. S.B. and R.C., listed in alphabetical order, contributed equally to this work.
  • Article
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    Background Heart rate variability (HRV) has proven to be a powerful non-invasive tool to investigate cardiac autonomic control and, seems to be influenced by nutritional status and exercise practice. However, the acute effects of fed or fasting states on HRV and blood pressure (BP) during low-to-moderate intensity aerobic exercise are currently unknown. Therefore, we investigated the baseline values and behavior of HRV, BP, and heart rate (HR) before and after low-to-moderate intensity aerobic exercise in fed and fasted states in healthy adults. Methods 12 healthy individuals with mean age (SD) 59.0 (9.1) years performed two tests on a treadmill at 80% of the mean velocity of the 6-min walking test separated by 48 h: 12 h fasted (FST) or 1 h fed (FED). HRV, BP and HR were analyzed at rest, posttest, and at the third, fifth, and seventh minutes of recovery. Results HRV and HR presented no significant alterations between nutritional conditions. HR at baseline was not different between nutritional conditions. Diastolic blood pressure was increased during the fasted baseline state. Conclusions The results of the current study provide that 12 h overnight fasting does not seem to be enough to affect significant changes in the autonomic modulation in healthy adults submitted to low-to-moderate intensity aerobic exercise.
  • Article
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    Introduction: Physical exercise in the fasting state has been a controversial topic; however, some studies have shown a greater loss of body fat and better glycemic control in those who participate in aerobic training when fasting. Aim: To evaluate the glycemic response after a session of moderate or vigorous physical exercise in young women in the state of fasting. Material and method: A randomized clinical trial was carried out. Twenty-six women (19 to 22 years old) were randomly assigned to two intervention groups. The first group was trained at an intensity of 70% of maximum heart rate (MHR) for 30 minutes, and the second group at an intensity of 90% MHR for 15 minutes. Height (cm), weight (Kg), body mass index (BMI), fat percentage, and maximum oxygen consumption (VO 2max) during a stress test were evaluated. Blood glucose levels were checked before and after the exercise session of each group. Results: No significant changes were found in post-exercise blood glucose levels in any experimental group, and the existing differences were not statistically significant. Conclusions: Moderate or vigorous physical exercise during fasting did not show significant variations in blood glucose, which suggests that it is safe for healthy young women to train when fasting.
  • Research
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    Objective: To investigate the effect of brisk walking in the fasted versus fed state on gastric emptying rate (GER), metabolic responses and appetite hormone responses. Subjects/methods: Twelve healthy men completed two 45 min treadmill walks, fasted (FASTED) and followed consumption of a standardised breakfast (FED). GER of a standardised lunch was subsequently measured for 2 h using the 13C-breath test method. Blood samples were collected at baseline, post-breakfast period, pre-exercise, immediately post exercise, pre-lunch then every 30 min following lunch for 2 h. Circulating concentrations of acylated ghrelin (GHR), glucagon-like peptide-1 (GLP-1), peptide tyrosine tyrosine (PYY), pancreatic polypeptide (PP), glucose, insulin, triglycerides, non-esterified fatty acids (NEFA) and cholesterol were measured. Subjective feelings of appetite were assessed at 15 min intervals throughout. Substrate utilisation was measured every 30 min, and continuously throughout exercise by indirect calorimetry. Results: No differences were observed for GER T½ (FASTED 89 ± 22 vs. FED 89 ± 24 min, P = 0.868) nor Tlag (FASTED 55 ± 15 vs. FED 54 ± 14 min, P = 0.704). NEFA concentrations were higher in FASTED at pre-exercise, post exercise and 30 min post exercise (pre-lunch) (all P < 0.05) but no differences were observed for glucose, cholesterol or triglycerides. Carbohydrate oxidation was greater at all time-points during FED exercise (all P < 0.05). Minimal changes in appetite were observed post lunch ingestion with no differences in PYY or GHR observed between trials. GLP-1 concentrations were greater in FED post-breakfast and pre-exercise (P < 0.05), though no differences were observed after lunch. A greater concentration of PP was observed in FED from pre-exercise to 30 min post lunch consumption (all P < 0.05). Insulin concentrations were higher in FED pre-exercise but higher in FASTED 1.5 h post lunch (P < 0.05). Conclusion: These findings suggest that gastrointestinal function, hunger and appetite regulatory hormones are not sensitive to low-intensity bouts of physical activity and holds positive implications for weight management practices.
  • Article
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    Consuming milk proteins (casein (CP) and whey (WP)) at night before sleep has been shown to positively influence next morning resting metabolic rate (RMR). No data exist regarding the effect of pre-sleep consumption of CP and WP on the ability to perform resistance exercise (RE) the following morning. The present study compared the effects of low (24 g) and high (48 g) doses of CP and WP and a non-energetic placebo (PLA) consumed 30 min before sleep on morning RMR, and RE performance. Nine active women participated in this randomized, double-blind, crossover study. Next morning RMR was measured via indirect calorimetry. RE was performed on six machines for 2 sets of 10 repetitions, and a 3rd set to failure at 60% of one-repetition maximum to calculate RE volume (weight lifted × sets × repetitions). Magnitude based inferences were used. Compared to the PLA, 48 g CP had a likely increase in RMR (4.0 ± 4.8%) and possibly trivial (1.1 ± 7.0%) effect on RE volume. There were no clear effects of 24 g CP, 24 g and 48 g of WP on RMR and RE volume. In conclusion, 48 g CP elicited favorable changes in morning RMR, with only trivial changes in RE performance.
  • Article
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    The role of an athlete’s dietary intake (both timing and food type) goes beyond simply providing fuel to support the body’s vital processes. Nutritional choices also have an impact on the metabolic adaptations to training. Over the past 20 years, research has suggested that strategically reducing carbohydrate (CHO) availability during an athlete’s training can modify the metabolic responses in lieu of simply maintaining a high CHO diet. Several methods have been explored to manipulate CHO availability and include: Low-carb, high-fat (LCHF) diets, performing two-a-day training without glycogen restoration between sessions, and a “sleep-low” approach entailing a glycogen-depleting session in the evening without consuming CHO until after a morning training session performed in an overnight fasted state. Each of these methods can confer beneficial metabolic adaptations for the endurance athlete including increases in mitochondrial enzyme activity, mitochondrial content, and rates of fat oxidation, yet data showing a direct performance benefit is still unclear.
  • Article
    The objective of this review paper is to evaluate the impact of undertaking aerobic exercise in the overnight-fasted v. fed-state, in the context of optimising the health benefits of regular physical activity. Conducting a single bout of aerobic exercise in the overnight-fasted v. fed-state can differentially modulate the aspects of metabolism and energy balance behaviours. This includes, but is not limited to, increased utilisation of fat as a fuel source, improved plasma lipid profiles, enhanced activation of molecular signalling pathways related to fuel metabolism in skeletal muscle and adipose tissue, and reductions in energy intake over the course of a day. The impact of a single bout of overnight-fasted v. fed-state exercise on short-term glycaemic control is variable, being affected by the experimental conditions, the time frame of measurement and possibly the subject population studied. The health response to undertaking overnight-fasted v. fed-state exercise for a sustained period of time in the form of exercise training is less clear, due to a limited number of studies. From the extant literature, there is evidence that overnight-fasted exercise in young, healthy men can enhance training-induced adaptations in skeletal muscle metabolic profile, and mitigate against the negative consequences of short-term excess energy intake on glucose tolerance compared with exercising in the fed-state. Nonetheless, further long-term studies are required, particularly in populations at-risk or living with cardio-metabolic disease to elucidate if feeding status prior to exercise modulates metabolism or energy balance behaviours to an extent that could impact upon the health or therapeutic benefits of exercise.
  • Article
    Objective The role of selective beta2-adrenergic stimulation in regulation of leg glucose uptake and free fatty acid (FFA) balance is inadequately explored in humans. The objective of this study was to investigate beta2-adrenergic effects on net leg glucose uptake and clearance, and FFA balance at rest and during exercise. Design The study was a randomized, placebo-controlled crossover trial, where 10 healthy men received either infusion of beta2-agonist terbutaline (0.2–0.4 mg) or placebo. Net leg glucose uptake and clearance, and FFA balance were determined at rest and during 8 min of knee-extensor exercise using Fick’s principle. Vastus lateralis muscle biopsies were collected at rest and at cessation of exercise. The primary outcome measure was net leg glucose uptake. Results At rest, net leg glucose uptake and clearance were 0.35 (±0.16) mmol×min⁻¹ and 41 (±17) mL×min⁻¹ (mean±95%CI) higher (p<0.001) for terbutaline than placebo, corresponding to increases of 84 and 70%. During exercise, no treatment differences were observed in net leg glucose uptake, whereas clearance was 101 (±86) mL×min⁻¹ lower (p<0.05) for terbutaline than placebo. At rest, terbutaline induced a net leg FFA release of 21 (±14) µmol×min⁻¹, being different from placebo (p=0.04). During exercise, net leg FFA uptake was not different between the treatments. Conclusions These observations indicate that beta2-agonist alters net leg glucose uptake and clearance, as well as FFA balance in humans, which is associated with myocellular beta2-adrenergic and insulin-dependent signaling. Furthermore, the study shows that exercise confounds the beta2-adrenergic effect on net leg glucose uptake and FFA balance.
  • Article
    This review aimed to verify the effect of exercise and meal timing on energy metabolism. Many people are exercising and playing sports in their own spare time. Although guidelines for daily exercise for healthy life suggest indications of intensity and frequency, there is no instruction about when exercise should be performed. However, there are some diurnal variations in energy metabolism responses to exercise and food intake. In addition, exercise performed before meals and vice versa are different stimuli to whole body energy metabolism, respectively. Further research is required to optimize that translating the results in laboratory to real life, because with growing diversity in lifestyle.
  • Article
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    The aim of this study was to investigate the effect of lactatemia elevation and glycemia reduction on strenuous swimming performance in fasted rats. Three rats were placed in a swimming tank at the same time. The first rat was removed immediately (control group) and the remaining ones were submitted to a strenuous swimming session. After the second rat was exhausted (Exh group), the third one was immediately removed from the water (Exe group). According to the period of time required for exhaustion, the rats were divided into four groups: low performance (3-7 min), low-intermediary performance (8-12 min), high-intermediary performance (13-17 min), and high performance (18-22 min). All rats were removed from the swimming tanks and immediately killed by decapitation for blood collection or anesthetized for liver perfusion experiments. Blood glucose, lactate, and pyruvate concentrations, blood lactate/pyruvate ratio, and liver lactate uptake and its conversion to glucose were evaluated. Exhaustion in low and low-intermediary performance were better associated with higher lactate/pyruvate ratio. On the other hand, exhaustion in high-intermediary and high performance was better associated with hypoglycemia. Lactate uptake and glucose production from lactate in livers from the Exe and Exh groups were maintained. We concluded that there is a time sequence in the participation of lactate/pyruvate ratio and hypoglycemia in performance during an acute strenuous swimming section in fasted rats. The liver had an important participation in preventing hyperlactatemia and hypoglycemia during swimming through lactate uptake and its conversion to glucose.
  • Article
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    : Protocols of systematic reviews and meta-analyses allow for planning and documentation of review methods, act as a guard against arbitrary decision making during review conduct, enable readers to assess for the presence of selective reporting against completed reviews, and, when made publicly available, reduce duplication of efforts and potentially prompt collaboration. Evidence documenting the existence of selective reporting and excessive duplication of reviews on the same or similar topics is accumulating and many calls have been made in support of the documentation and public availability of review protocols. Several efforts have emerged in recent years to rectify these problems, including development of an international register for prospective reviews (PROSPERO) and launch of the first open access journal dedicated to the exclusive publication of systematic review products, including protocols (BioMed Central's Systematic Reviews). Furthering these efforts and building on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines, an international group of experts has created a guideline to improve the transparency, accuracy, completeness, and frequency of documented systematic review and meta-analysis protocols--PRISMA-P (for protocols) 2015. The PRISMA-P checklist contains 17 items considered to be essential and minimum components of a systematic review or meta-analysis protocol.This PRISMA-P 2015 Explanation and Elaboration paper provides readers with a full understanding of and evidence about the necessity of each item as well as a model example from an existing published protocol. This paper should be read together with the PRISMA-P 2015 statement. Systematic review authors and assessors are strongly encouraged to make use of PRISMA-P when drafting and appraising review protocols.
  • Article
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    Background: As part of the growing lifestyle diversity in modern society, there is wide variation in the time of day individuals choose to exercise. Recent surveys in the US and Japan have reported that on weekdays, more people exercise in the evening, with fewer individuals exercising in the morning or afternoon. Exercise performed in the post-prandial state has little effect on accumulated fat oxidation over 24 h (24-h fat oxidation) when energy intake is matched to energy expenditure (energy-balanced condition). The present study explored the possibility that exercise increases 24-h fat oxidation only when performed in a post-absorptive state, i.e. before breakfast. Methods: Indirect calorimetry using a metabolic chamber was performed in 10 young, non-obese men over 24 h. Subjects remained sedentary (control) or performed 60-min exercise before breakfast (morning), after lunch (afternoon), or after dinner (evening) at 50% of VO2max. All trials were designed to be energy balanced over 24 h. Time course of energy and substrate balance relative to the start of calorimetry were estimated from the differences between input (meal consumption) and output (oxidation). Findings: Fat oxidation over 24 h was increased only when exercise was performed before breakfast (control, 456 ± 61; morning, 717 ± 64; afternoon, 446 ± 57; and evening, 432 ± 44 kcal/day). Fat oxidation over 24 h was negatively correlated with the magnitude of the transient deficit in energy and carbohydrate. Interpretation: Under energy-balanced conditions, 24-h fat oxidation was increased by exercise only when performed before breakfast. Transient carbohydrate deficits, i.e., glycogen depletion, observed after morning exercise may have contributed to increased 24-h fat oxidation.
  • Article
    Systematic reviews and meta-analyses are essential to summarize evidence relating to efficacy and safety of health care interventions accurately and reliably. The clarity and transparency of these reports, however, is not optimal. Poor reporting of systematic reviews diminishes their value to clinicians, policy makers, and other users. Since the development of the QUOROM (QUality Of Reporting Of Meta-analysis) Statement-a reporting guideline published in 1999-there have been several conceptual, methodological, and practical advances regarding the conduct and reporting of systematic reviews and meta-analyses. Also, reviews of published systematic reviews have found that key information about these studies is often poorly reported. Realizing these issues, an international group that included experienced authors and methodologists developed PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) as an evolution of the original QUOROM guideline for systematic reviews and meta-analyses of evaluations of health care interventions. The PRISMA Statement consists of a 27-item checklist and a four-phase flow diagram. The checklist includes items deemed essential for transparent reporting of a systematic review. In this Explanation and Elaboration document, we explain the meaning and rationale for each checklist item. For each item, we include an example of good reporting and, where possible, references to relevant empirical studies and methodological literature. The PRISMA Statement, this document, and the associated Web site (www.prisma-statement.org) should be helpful resources to improve reporting of systematic reviews and meta-analyses.
  • Article
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    Disturbances in fat oxidation have been associated with an increased risk of obesity and metabolic disorders such as insulin resistance. There is large inter-subject variability in the capacity to oxidize fat when physically active although the significance of this for metabolic health is unclear. We investigated whether the maximal capacity to oxidize fat during exercise is related to 24 hour (h) fat oxidation and insulin sensitivity. Maximal Fat Oxidation (MFO; indirect calorimetry during incremental exercise) and insulin sensitivity (Quantitative Insulin Sensitivity Check Index, QUICKI) was measured in 53 young, healthy men (age 24±7 y; V̇O2max 52±6 ml/kg/min). 24 h Fat Oxidation (24 h FO; indirect calorimetry) was assessed in 16 young, healthy men (age 26±8 y; V̇O2max 52±6 ml/kg/min) during a 36 h stay in a whole-room respiration chamber. MFO (g/min) was positively correlated with 24 h FO (g/d) (R=0.65, P=0.003; R=0.46, P=0.041 when controlled for V̇O2max [L/min]), 24 h % energy from FO (R=0.58, P=0.009) and insulin sensitivity (R=0.33, P=0.007). MFO (g/min) was negatively correlated with 24 h fat balance (g/d) (R=-0.51, P=0.021) but not significantly correlated with 24 h RQ (R=-0.29, P=0.142). While further investigations are needed, our data showing positive associations between maximal fat oxidation and 24 h fat oxidation, and maximal fat oxidation and insulin sensitivity, in healthy young men suggests that a high capacity to oxidize fat whilst physically active could be advantageous for the maintenance of metabolic health. Copyright © 2015, Journal of Applied Physiology.
  • Article
    Full-text available
    Protocols of systematic reviews and meta-analyses allow for planning and documentation of review methods, act as a guard against arbitrary decision making during review conduct, enable readers to assess for the presence of selective reporting against completed reviews, and, when made publicly available, reduce duplication of efforts and potentially prompt collaboration. Evidence documenting the existence of selective reporting and excessive duplication of reviews on the same or similar topics is accumulating and many calls have been made in support of the documentation and public availability of review protocols. Several efforts have emerged in recent years to rectify these problems, including development of an international register for prospective reviews (PROSPERO) and launch of the first open access journal dedicated to the exclusive publication of systematic review products, including protocols (BioMed Central's Systematic Reviews). Furthering these efforts and building on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines, an international group of experts has created a guideline to improve the transparency, accuracy, completeness, and frequency of documented systematic review and meta-analysis protocols-PRISMA-P (for protocols) 2015. The PRISMA-P checklist contains 17 items considered to be essential and minimum components of a systematic review or meta-analysis protocol.This PRISMA-P 2015 Explanation and Elaboration paper provides readers with a full understanding of and evidence about the necessity of each item as well as a model example from an existing published protocol. This paper should be read together with the PRISMA-P 2015 statement. Systematic review authors and assessors are strongly encouraged to make use of PRISMA-P when drafting and appraising review protocols. © BMJ Publishing Group Ltd 2014.
  • Article
    Whole body fat oxidation increases during exercise. However, 24-h fat oxidation on a day with exercise often remains similar to that of sedentary day, when energy intake is increased to achieve an energy-balanced condition. The present study aimed to examine a possibility that time of the day when exercise is performed makes differences in 24-h fat oxidation. As a potential mechanism of exercise affecting 24-h fat oxidation, its relation to exercise-induced transient energy deficit was examined. Nine young male endurance athletes underwent three trials of indirect calorimetry using a metabolic chamber, in which they performed a session of 100 min of exercise before breakfast (AM), after lunch (PM), or two sessions of 50 min of exercise before breakfast and after lunch (AM/PM) at 65% of maximal oxygen uptake. Experimental meals were designed to achieve individual energy balance. Twenty-four-hour energy expenditure was similar among the trials, but 24-h fat oxidation was 1,142 ± 97, 809 ± 88, and 608 ± 46 kcal/24 h in descending order of its magnitude for AM, AM/PM, and PM, respectively (P < 0.05). Twenty-four-hour carbohydrate oxidation was 2,558 ± 110, 2,374 ± 114, and 2,062 ± 96 kcal/24 h for PM, AM/PM, and AM, respectively. In spite of energy-balanced condition over 24 h, exercise induced a transient energy deficit, the magnitude of which was negatively correlated with 24-h fat oxidation (r = -0.72, P < 0.01). Similarly, transient carbohydrate deficit after exercise was negatively correlated with 24-h fat oxidation (r = -0.40, P < 0.05). The time of the day when exercise is performed affects 24-h fat oxidation, and the transient energy/carbohydrate deficit after exercise is implied as a factor affecting 24-h fat oxidation. Copyright © 2015 the American Physiological Society.
  • Article
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    Background: The early detection of glucose metabolism impairment is a very important goal, mainly in individuals with a family history of diabetes (FHD) or in those with borderline insulin resistance (BIR: HOMA-IR > 2.0). Aims/hypothesis: To document the differences in glucose metabolism between healthy subjects with and without FHD and with BIR, in response to a maximal exercise test in both fasting and postprandial conditions. Methods: Twenty nine healthy and physically active subjects (15 female and 14 male) volunteered to participate in three maximal exercise tests, in fasting and postprandial states. Maximal O2 consumption, heart rate, blood pressure, anthropometry, glucose (basal and after exercise), and insulin measurements were obtained. Results: glycemia diminished at the end of maximal exercise and decreased the most in FHD and/or HOMA-IR > 2.0 compared to without FHD and/or HOMA-IR < 2.0. Recovery of post-exercise glycemia was slower in subjects with FHD and HOMA-IR > 2.0. Conclusions: the maximal exercise test in fasting or postprandial conditions proved to detect glucose metabolism differences between subjects with vs. without FHD and with vs. without BIR.