Night-time consumption of protein or carbohydrate results in increased morning resting energy expenditure in active college-aged men

Abstract

The purpose of the present study was to investigate whether whey protein (WP), casein protein (CP), carbohydrate (CHO) or a non-energy-containing placebo (PLA) consumed before sleep alters morning appetite and resting energy expenditure (REE) in active men. A total of eleven men (age: 23·6 (sem 1·0) years; body fat: 16·3 (sem 2·5) %) participated in this randomised, double-blind, cross-over study. A single dose of WP (30 g), CP (30 g), CHO (33 g) or PLA was consumed 30 min before sleep, and each trial was separated by 48-72 h. The next morning (05.00-08.00 hours), measurements of satiety, hunger and desire to eat and REE were taken. After a 30 min equilibration period, REE in the supine position was measured for 60 min. An analysis of 10 min mean intervals over the final 50 min of the measurement period was conducted. Statistical analyses were conducted using repeated-measures ANOVA for metabolic variables, and a one-way ANOVA was used for measuring changes in appetite markers. Group differences were examined by Tukey's post hoc analysis. There were no significant differences in appetite measures among the groups. There was a main group effect for REE. The predicted REE was significantly greater after consumption of the WP (8151 (sem 67) kJ/d), CP (8126 (sem 67) kJ/d) and CHO (7988 (sem 67) kJ/d) than after that of the PLA (7716 (sem 67) kJ/d, P <0·0001). There were no significant differences between the WP and CP groups in any metabolic measurements. Night-time consumption of WP, CP or CHO, in the hours close to sleep, elicits favourable effects on the next-morning metabolism when compared with that of a PLA in active young men.

Full text

Night-time consumption of protein or carbohydrate results in increased
morning resting energy expenditure in active college-aged men
Takudzwa A. Madzima, Lynn B. Panton, Sarah K. Fretti, Amber W. Kinsey and Michael J. Ormsbee*
Department of Nutrition, Food and Exercise Sciences, Institute of Sports Science and Medicine, The Florida State University,
120 Convocation Way, 430 Sandels Building, Tallahassee, FL 32311, USA
(Submitted 14 December 2012 – Final revision received 15 May 2013 – Accepted 16 May 2013 – First published online 17 June 2013)
Abstract
The purpose of the present study was to investigate whether whey protein (WP), casein protein (CP), carbohydrate (CHO) or a
non-energy-containing placebo (PLA) consumed before sleep alters morning appetite and resting energy expenditure (REE) in active
men. A total of eleven men (age: 23·6 (SEM 1·0) years; body fat: 16·3 (SEM 2·5) %) participated in this randomised, double-blind, cross-
over study. A single dose of WP (30 g), CP (30 g), CHO (33 g) or PLA was consumed 30 min before sleep, and each trial was separated
by 48–72 h. The next morning (05.00–08.00 hours), measurements of satiety, hunger and desire to eat and REE were taken. After a
30 min equilibration period, REE in the supine position was measured for 60 min. An analysis of 10 min mean intervals over the final
50 min of the measurement period was conducted. Statistical analyses were conducted using repeated-measures ANOVA for metabolic
variables, and a one-way ANOVA was used for measuring changes in appetite markers. Group differences were examined by Tukey’s
post hoc analysis. There were no significant differences in appetite measures among the groups. There was a main group effect for
REE. The predicted REE was significantly greater after consumption of the WP (8151 (SEM 67) kJ/d), CP (8126 (SEM 67) kJ/d) and CHO
(7988 (SEM 67) kJ/d) than after that of the PLA (7716 (SEM 67) kJ/d, P,0·0001). There were no significant differences between the WP
and CP groups in any metabolic measurements. Night-time consumption of WP, CP or CHO, in the hours close to sleep, elicits favourable
effects on the next-morning metabolism when compared with that of a PLA in active young men.
Key words: RMR: Night-time eating: Whey protein: Casein protein
It is well known that proteins elicit greater thermic effects,
increase resting energy expenditure (REE)
(1 – 3)
and satiety
(4,5)
and decrease respiratory exchange ratios in the immediate
postprandial period
(1,6,7)
when compared with carbohydrates
(CHO) and fats. Furthermore, the addition of a protein
supplement to a normal diet promotes weight loss and main-
tenance, mainly as a result of increases in satiety
(8,9)
and
energy expenditure
(1,10,11)
.
The positive physiological effects of protein consumption
have primarily been observed in studies investigating the post-
prandial effects of mixed meals consumed in the morning and
afternoon
(11 – 14)
or after consumption of single macronutrients
in the hours close to exercise
(15 – 17)
. However, less is known
about the effects of different macronutrients consumed in
the late evening within 30 to 60 min of sleep on the desire
to eat and REE the following morning.
Night-time eating is a largely unexplored component of
nutrient timing studies and could be a key factor that plays
an instrumental role in the modulation of the effects of differ-
ent macronutrients on body composition, metabolism and
satiety. Until recently, the majority of the information regard-
ing what individuals should be consuming at night has been
anecdotal and based on the idea that late-evening ingestion
of food will increase the likelihood of weight gain
(18)
. The
potential for weight gain with late-evening food consumption
is plausible given that both metabolic rate
(19)
and satiety
(18)
are reduced during this time, which may favour a positive
energy balance. For this reason, it has been recommended
that individuals concerned with weight regulation avoid
consuming energy-containing products in the hours close to
sleep due to the potential body composition implications associ-
ated with increased food intake and attenuated physiological
functioning. However, this is not the case for physically active
individuals who would probably benefit from a constant flow
of nutrients that may be necessary for optimal recovery both
post-exercise and during the overnight period
(17,20)
.
Interestingly, the milk proteins, whey protein (WP) and
casein protein (CP), are digested and absorbed at different
rates
(21)
. CP has been described as a ‘slow protein’ due to
the slower digestion and absorptive rates observed compared
*Corresponding author: M. J. Ormsbee, fax þ1 850 645 5000, email mormsbee@fsu.edu
Abbreviations: CHO, carbohydrate; CP, casein protein; PLA, non-energy-containing placebo; REE, resting energy expenditure; WP, whey protein.
British Journal of Nutrition (2014), 111, 71–77 doi:10.1017/S000711451300192X
qThe Authors 2013
British Journal of Nutrition

with those of WP, and therefore CP has popularly been
recommended as a night-time protein
(21)
. Furthermore, in
some
(6,7)
, but not all
(14)
, studies, CP has been shown to
increase satiety and reduce appetite to a greater extent
when compared with WP. Recently, Res et al.
(17)
have
reported that oral CP consumption before sleep results in
elevated muscle protein synthesis throughout the sleeping
hours compared with non-energy-containing placebo (PLA)
consumption in healthy young men after a resistance exercise
bout. Another study carried out in this laboratory has demon-
strated that CP administered via nasogastric tubing during
sleep increased overnight muscle protein synthesis in elderly
men
(22)
. These data highlight the potential benefits of pro-
viding a constant flow of nutrients through night-time protein
intake. It is possible that night-time protein intake may be
a new window of opportunity for physiological benefits
and, in the long term, optimal performance, but no studies
have compared the effects of different proteins consumed
before bed.
Therefore, the present study investigated the extent to
which a single serving of WP, CP, CHO or a PLA before
sleep affects satiety and metabolism, independent of exercise,
in healthy, physically active young men. We hypothesised
that consumption of protein at night before sleep would
have a positive impact on next-morning metabolism and appe-
tite to a greater extent than that of CHO or a PLA beverage.
Methods
Participants
In the present study, eleven physically active ($4 d/week
and 50 min/d of self-reported moderate-to-vigorous physical
activity for .12 months) college-aged men (age: 23·6 (SEM 1·0)
years; height: 183·1 (SEM 2·2) cm; weight: 86·2 (SEM 3·5) kg; BMI:
25·8 (SEM 0·8) kg/m
2
; and body fat: 16·3 (SEM 2·5) %) parti-
cipated. Participants were excluded if they had uncontrolled
hypertension (blood pressure .160/100 mmHg), were taking
blood pressure or cholesterol medications, or had been
diagnosed with CVD, stroke, diabetes, or thyroid or kidney
dysfunction or had milk allergies. Additionally, all smokers
were excluded. The participants were asked to refrain from
taking any nutritional supplements (except for a multivitamin)
for 2 weeks before their first laboratory visit and throughout
the duration of the study. In addition, the participants were
asked to maintain their usual exercise regimen for the duration
of the study. The present study was conducted according
to the guidelines laid down in the Declaration of Helsinki,
and all procedures involving human participants were
approved by the Florida State University Institutional Review
Board. Written informed consent was obtained before partici-
pation in the study.
Study design
The study had a randomised, double-blind, cross-over
design. Before the start of the study, the participants
reported to the laboratory for baseline measurements of
height (Seca Corporation), weight (Detecto
w
; DETECTO
Scale Company), waist and hip circumferences (Creative
Health Products, Inc.), and body composition via air-displace-
ment plethysmography (BOD POD
w
; COSMED). WP and CP
are the commonly consumed supplements by physically
active individuals and have been associated with improve-
ments in many physiological outcomes
(17,22 – 24)
. Therefore,
these proteins were administered in the present study. The fol-
lowing four supplements were randomly consumed with each
trial being separated by 48–72 h: (1) WP (38 g, 628 kJ
(150 kcal), 30 g protein, 3 g CHO and 2 g fat); (2) CP (38 g,
586 kJ (140 kcal), 30 g protein, 3 g CHO and 1 g fat); (3) CHO
(maltodextrin; 38 g, 628 kJ (150 kcal), 0 g protein, 33 g CHO
and 2 g fat); (4) PLA (2·9 g, 0 kJ (0 kcal); Propel Zeroe;
PepsiCo Inc.). Powdered WP, CP and CHO were labelled A,
B and C and packaged by an external investigator who was
not otherwise involved in the study. All powders were fla-
voured identically (vanilla chai) and had an identical texture
to ensure that the participants were truly blinded to each
experimental trial. The non-energy-containing PLA (Propel
Zeroe) was also in a powdered form and was labelled as sup-
plement D. The flavour and consistency of the PLA were
different from those of the WP, CP and CHO powders. There-
fore, the PLA was single blinded and not double blinded to the
participants. The administered dose of 30 g was chosen
because it has previously been shown to be ideal for healthy,
physically active men
(25,26)
, and the 627 kJ (150 kcal) serving
was chosen in an attempt to offer a reasonable energetic
load that mimics many manufactured protein beverages. All
supplements were consumed at home with 12 oz of water as
the last food or energy-containing beverage of the day,
taken at least 1 h following consumption of the participant’s
last evening meal and within 30 min of going to sleep. The
morning following the evening consumption (05.00 – 08.00
hours), the participants reported to the laboratory for the
measurement of satiety and metabolism.
On two consecutive days before each experimental trial,
all the participants completed a dietary log and were asked
to replicate this eating pattern before each visit. Compliance
was verified by the analysis of food records by the same
research technician (United States Department of Agricul-
ture, www.choosemyplate.gov). Furthermore, the participants
were instructed to refrain from consuming caffeine or alcohol
and undertaking any planned physical activity 24 h before
each visit.
Hunger, satiety and desire to eat assessment
Upon arrival to the laboratory on each test morning, the parti-
cipants completed a visual analogue scale
(27)
to subjectively
assess hunger, satiety and desire to eat. The visual analogue
scale is a 100 mm horizontal scale with opposing extremes
(‘not at all’ to ‘extremely’) of each appetite sensation (hunger,
satiety and desire to eat) anchored at each end of the 100 mm
line. The participants indicated their subjective feelings by pla-
cing a vertical line along the 100 mm scale, and each rating
was converted to a score in mm using a standard ruler. Higher
scores indicated greater feelings of each sensation.
T. A. Madzima et al.72
British Journal of Nutrition

Resting energy expenditure
Following the visual analogue scale measurements, the
participants were asked to lie supine on a bed in a dark,
quiet and climate-controlled room (20–228C) for 30 min in
an effort to have them feel completely rested. Gas exchange
was then measured continuously for 60 min to assess VO
2
(ml/kg per min), REE (kcal/d) and respiratory quotient via
indirect calorimetry using a ventilated hood (TrueOne 2400
metabolic cart; ParvoMedics). The last 50 min of the data
collection period were used for analysis and compared
across five 10 min segments over the last 50 min period.
The test–retest intra-class CV for the measurement of REE
in our laboratory is 1·7 %.
Anthropometrics and body composition
Upon completion of the metabolic measurements, the
participants had their height and weight measured without
shoes while wearing only spandex shorts to the nearest
0·1 cm and 0·1 kg, respectively, via a wall-mounted stadio-
meter (Seca Corporation) and a digital scale (Detecto
w
).
Waist and hip circumferences were taken a minimum of
two times using a Gulick fibreglass measuring tape with
a tension handle (Creative Health Products, Inc.). Additional
measurements were taken if duplicate readings were in
excess of 5 mm of each other, until the discrepancy between
the two readings was equal to or less than 5 mm. Body com-
position (% body fat, lean and fat mass) was measured with
the participants wearing spandex shorts and a lycra cap
over their hair via air-displacement plethysmography (BOD
POD
w
; COSMED)
(28)
.
Statistical analyses
Statistical analyses were conducted using JMP Pro 10 (SAS).
A4£5 (group £time) repeated-measures ANOVA was con-
ducted to measure differences during each of the five 10 min
segments of the final 50 min period of indirect calorimetry.
A one-way ANOVA was conducted for the measurement
of hunger, satiety and desire to eat for each trial. Tukey’s
post hoc analysis was used where appropriate to examine
group differences. A Shapiro test was used to ensure normality
for body fat percentage and BMI. Significance was set at
P,0·05, and data are reported as mean with their standard
errors, unless otherwise noted.
Results
There were no differences in total energy, protein, CHO or
fat consumed before any of the four experimental trials.
The analysis of the 2 d dietary logs indicated that an average
of 9223 (SEM 3169) kJ/d (2204 (SEM 757) kcal/d) was consumed
(19·9 (SEM 6·6) % protein, 48·4 (SEM 9·5) % CHO and 30·8
(SEM 8·2) % fat).
Subjective assessments of hunger, satiety and desire to eat
are presented in Table 1. No significant differences were
observed for hunger, satiety or desire to eat among the WP,
CP, CHO and PLA groups. However, although not statistically
significant, satiety (feeling of fullness) after consumption of
both WP (40·6 (SEM 5·4) mm) and CP (45·4 (SEM 0·4) mm)
Table 1. Visual analogue scale of hunger, satiety and desire to eat (n11)
(Mean values with their standard errors)
CHO WP CP PLA
Mean SEM Mean SEM Mean SEM Mean SEM
Hunger (mm) 44·4 6·74 39·4 6·74 36·6 6·74 44·1 6·74
Satiety (mm) 36·1 5·42 40·6 5·42 45·4 5·42 33·9 5·42
Desire to eat (mm) 43·2 7·20 43·4 7·20 40·6 7·20 53·3 7·20
CHO, carbohydrate; WP, whey protein; CP, casein protein; PLA, placebo.
3·0
3·1
3·2
3·3
3·4
3·5
(a)
*
Experimental trial
PLA CHO WP CP
10 20 30 40 50
VO2 (ml/kg per min)
3·0
3·1
3·2
3·3
3·4
3·5
Time (min)
(b)
VO2 (ml/kg per min)
Fig. 1. (a) VO
2
(ml/kg per min) and (b) 10 min intervals of VO
2
(ml/kg per
min) for 50 min the morning after night-time consumption of a single serving
of whey protein (WP), casein protein (CP), maltodextrin (CHO) and a
non-energetic placebo (PLA). Values are means, with their standard errors
represented by vertical bars. * Mean value was significantly different from
that of WP and CP (P,0·05). (b) , PLA; , CHO; , WP; , CP.
Night-time eating and energy expenditure 73
British Journal of Nutrition

was greater than that after consumption of CHO (36·1
(SEM 5·4) mm) and PLA (33·9 (SEM 5·4) mm). Metabolic assess-
ment of VO
2
(ml/kg per min) was done continuously for
60 min, and 10 min mean intervals from the final 50 min
period were analysed (Fig. 1). There were no group £time
interactions or time effects; however, there were group differ-
ences. Mean VO
2
(ml/kg per min) for the WP (3·35
(SEM 0·03) ml/kg per min) and CP (3·30 (SEM 0·03) ml/kg per
min) groups were significantly (P,0·0001) greater than
those for the PLA group (3·16 (SEM 0·03) ml/kg per min) but
not for the CHO group (3·25 (SEM 0·03) ml/kg per min)
(Fig. 1(a)). Additionally, there were no significant differences
between the WP and CP groups or between the CHO and PLA
groups for VO
2
(Fig. 1). Interestingly, although not statistically
significant, the PLA group had a lower VO
2
at 20, 30, 40 and
50 min than the WP, CP and CHO groups (Fig. 1(b)).
The predicted REE (kJ/d; kcal/d) measurements during
10 min mean intervals from the final 50 min of the data
collection period are presented in Fig. 2. There were no
group £time interactions or time effects; however, there
were group differences. The predicted REE was significantly
greater after consumption of the WP (8151 (SEM 65) kJ/d; 1947
(SEM 16) kcal/d), CP (8126 (SEM 65) kJ/d; 1941 (SEM 16) kcal/d)
and CHO (7988 (SEM 65) kJ/d; 1908 (SEM 16) kcal/d) than after
that of the PLA (7716 (SEM 65) kJ/d; 1843 (SEM 16) kcal/d;
P,0·0001). There were no significant differences between
the WP, CP and CHO groups. Similar to that observed for
VO
2
, there were no differences at baseline (minute 10) and,
although not significant, the PLA group had the lowest REE
at all the other time points. Respiratory quotient (VCO
2
/VO
2
)
was significantly lower after consumption of the PLA
(0·76 (SEM 0·003)) than after that of the WP (0·77 (SEM 0·003))
and CHO (0·77 (SEM 0·003); P,0·0001), but not after that of
the CP (0·76 (SEM 0·003)) (Fig. 3).
Discussion
The ability of proteins to increase thermogenesis, and
therefore REE, to a greater extent than CHO has been well
documented in acute studies
(1,6,29 – 31)
. The positive physio-
logical effects of proteins have been observed after daytime
consumption
(1,7,32)
or in the hours close to resistance exer-
cise
(15,17,33)
. However, to our knowledge, no studies have
investigated satiety or REE changes after protein consumption
before sleep, and none has compared then after WP, CP and
CHO consumption during this time frame.
The main findings of the present study are that there
were no differences between the effects of protein and CHO
on morning REE or subjective feelings of satiety when con-
sumed before sleep in healthy, physically active young men.
Furthermore, there were no significant differences between
the effects of WP and CP consumption on morning REE. Inter-
estingly, the WP, CP and CHO elicited a significantly greater
effect on morning REE than the PLA. Our data suggest that,
regardless of the macronutrient type, consuming 586 –628 kJ
(140 –150 kcal) of a supplement in liquid form before bed
has a superior effect on morning VO
2
and REE than going
to bed on an empty stomach. This finding has relevance to
healthy, physically active individuals and may extend to popu-
lations that are trying to lose and/or maintain body weight.
0·75
0·76
0·77
0·78
0·79
0·80
*
Experimental trial
PLA CHO WP CP
RQ (VCO2/VO2)
Fig. 3. Respiratory quotient (RQ) the morning after night-time consumption
of a single serving of whey protein (WP), casein protein (CP), maltodextrin
(CHO) and a non-energetic placebo (PLA). Values are means, with their
standard errors represented by vertical bars. * Mean value was significantly
different from that of WP and CHO (P,0·05), but not CP.
7600
7800
8000
8200
8400
8600
(a)
*
Experimental trial
PLA CHO WP CP
7200
7400
7600
7800
8000
8200
8400
8600
REE (kJ/d) REE (kJ/d)
Time (min)
10 20 30 40 50
(b)
Fig. 2. (a) Predicted resting energy expenditure (REE, kJ/d) and (b) 10 min
intervals of predicted REE (kJ/d) for 50 min the morning after night-time
consumption of a single serving of whey protein (WP), casein protein (CP),
maltodextrin (CHO) and a non-energetic placebo (PLA). Values are means,
with their standard errors represented by vertical bars. * Mean value was
significantly different from that of WP, CP and CHO (P,0·05). (b) , PLA;
, CHO; , WP; , CP.
T. A. Madzima et al.74
British Journal of Nutrition

Traditional practice has been to limit energy intake in the late
evening in an attempt to prevent storing energy consumed as
fat because metabolism is thought to slow during sleep.
Although metabolism has been shown to slow at night
(19)
,
no scientific evidence has shown this to be true after consum-
ing food before sleep. Our findings suggest that energy intake
of 586 –628 kJ (140 – 150 kcal) before sleep actually increases
VO
2
and predicted REE.
It is well documented that proteins have a superior thermo-
genic and satiating effect than CHO and fats, and still less is
known whether differences exist between protein types. In
agreement with the present results, Lorenzen et al.
(32)
reported
no differences in postprandial REE between three 1465 kJ
(350 kcal) mixed breakfast meals, each containing 36 g WP,
34 g CP or milk (28 g casein and 7 g whey). In contrast, Ache-
son et al.
(1)
found the thermic effect of 1921 kJ (459 kcal) of a
WP mixed meal to be greater than that of isoenergetic casein
and soya protein meals and found all protein groups to have a
greater thermogenic effect than 1921 kJ (459 kcal) of CHO in
twenty-three healthy lean men and women. Moreover, 30 g
of WP (502 kJ or 120 kcal) did not affect REE in middle-aged
women and decreased fat oxidation compared with a
non-energetic placebo when consumed immediately post-
exercise
(33)
. These conflicting findings demonstrate the need
for more research investigating the effect of protein choice,
particularly at night, on metabolism. Furthermore, the
energy consumed in the experimental trials of the aforemen-
tioned studies varied and were different from the 586– 628 kJ
(140 –150 kcal) used in the present study. Therefore, future
research should focus on determining the optimum energetic
load needed to elicit favourable changes in REE. Nevertheless,
consumption of 40 g of CP before sleep has been shown to
stimulate muscle protein synthesis overnight in both
young
(17)
and elderly
(22)
men, and it is likely that, in the
long term, this increase in muscle protein synthesis will
result in an increase in REE. The energy load reported by
these studies is at least 669 kJ (160 kcal), which is very similar
to the energy load observed in the present study. However,
these authors did not specify whether any additional energy
was provided by their casein supplement, so a true compari-
son is not possible.
When compared with CHO, several studies have observed
an increased satiating effect of protein-rich breakfast and
lunch in the postprandial period
(3,8,34,35)
. Although not signifi-
cant, the present results indicate that a single serving of WP or
CP before sleep has a greater satiating effect than that of CHO.
The present results are in agreement with those reported by
Bowen et al.
(35)
, who found proteins to improve satiety
more than CHO. Although the improved satiating effect of
proteins compared with that of CHO has been demonstrated,
the debate regarding which type of protein best modulates
satiety is ongoing. The satiating effects of certain proteins
may be dose dependent, as shown by Smeets et al.
(36)
, who
reported energy expenditure and satiety to be acutely
improved after consumption of a single high-protein lunch
(25 % energy from protein) than after that of an adequate pro-
tein meal (10 % energy from protein) in thirty healthy men and
women (P,0·02) with each meal comprising 35 % of each
participant’s daily energy requirements. More recently,
Veldhorst et al.
(12 – 14)
have examined the effects of a mixed
breakfast meal containing whey, casein or soya protein at
fixed doses (20 % of daily energy requirement) on satiety for
4 h after ingestion in thirty healthy men and women. A break-
fast containing 10 % energy from whey was more satiating
than that containing 10 % casein at all time points and 10 %
soya 20 min after breakfast (P,0·05)
(14)
. There were no
differences between proteins at 25 % energy intake, an
intake considered higher than normal, suggesting that after
a certain amino acid threshold, whey, casein and soya as
part of a breakfast have similar satiating effects
(14)
. The
dose-dependent effects of different proteins on subjective
assessments of satiety may explain the similarities between
the WP and CP treatments in the present study, as both
used 30 g of the respective proteins.
There are a number of potential reasons for the discrepancy
between the findings of the aforementioned studies and our
findings. To date, the effects on satiety have been reported
after daytime protein consumption and typically as part of a
mixed meal. The present study, however, investigated the
effects of a single serving of different proteins consumed
before sleep on morning (8– 10 h later) satiety. Furthermore,
we measured subjective feelings of hunger, satiety and
desire to eat several hours after consumption of the WP, CP,
CHO or PLA. Thus, the elapsed time may have contributed
to the lack of significant differences in the measures of satiety.
In addition, it has also been reported that individuals with
habitually high protein intakes have a diminished satiating
response to a single protein meal
(37)
. As our participants
were active college-aged men, their diets may have contained
higher-than-standard protein amounts (1·3 g/kg per d; 19·8
(SEM 5·3) % protein), which may explain the lack of a signifi-
cant effect on appetite in the present study. Furthermore,
Groen et al.
(22)
reported that overnight administration of
40 g of casein elicited normal dietary protein digestion and
absorption kinetics. In addition, during the 5 h overnight post-
prandial period, the authors observed that the amount of
available circulating protein from the casein bolus was similar
to that observed after whey consumption during the day.
In addition, other authors have reported similar amino acid
availability 5 h following morning whey or casein consump-
tion
(38 – 40)
. These findings suggest similar protein digestion
and absorption kinetics overnight between the WP and CP,
thereby possibly explaining our lack of significant differences
between protein types.
Further inconsistency exists in the literature with regard to
macronutrient type and fat oxidation. Similar to our findings,
Benton et al.
(33)
reported fat oxidation (respiratory exchange
ratios) to be significantly diminished after 30 g post-exercise
whey supplementation (502 kJ or 120 kcal) 120 min after con-
sumption compared with PLA supplementation (P¼0·02). We
found fat oxidation, as assessed by respiratory exchange
ratios, to be significantly lower after consumption of the WP
and CHO (P¼0·0003) but not after that of the CP. WP has
been shown to have significantly (P,0·05) lower
(1)
and
higher
(32)
respiratory exchange ratio values than CHO and
CP, respectively. Interestingly, in the present study, in addition
Night-time eating and energy expenditure 75
British Journal of Nutrition

to having a significantly greater REE and VO
2
response, the CP
group had a response similar to that of the PLA group for fat
oxidation. While we were unable to collect blood in the pre-
sent study, Pennings et al.
(23)
reported that casein ingestion
results in a significantly lower insulin response when com-
pared with WP or CHO ingestion. Insulin can dramatically
lower fat oxidation, and this could explain the small differ-
ences in fat oxidation that we observed. The slow-digesting
nature of CP may have resulted in a blunted insulin response,
thereby resulting in greater fat utilisation when compared with
the faster-digesting WP and CHO. Therefore, it is plausible
that in addition to improving REE, CP may be an ideal macro-
nutrient for utilising fat as a fuel source in the late evening.
A few limitations exist and need to be addressed. Differ-
ences in taste, serving size and texture of the PLA may have
confounded the subjective feelings of hunger, satiety and
desire to eat. However, the decision to add a non-energy-
containing PLA was necessary for the measurements of VO
2
and REE to identify differences between energy intake and
not consuming energy before sleep. Likewise, although we
randomised the order of each experimental trial and required
a 48– 72 h washout period between laboratory visits, it is
possible that the order of treatments may have confounded
our findings. Furthermore, although purely speculation, the
physical differences between the PLA and WP/CP/CHO sup-
plements would probably have little impact on metabolic
measurements via indirect calorimetry. In addition, the ques-
tion remains as to whether the energy load of the ingested
supplements was offset by the increase in REE over the sleep-
ing hours or the next day. Therefore, future research should
investigate metabolism through the overnight period and for
a duration longer than 60 min the following morning to fully
understand any weight management implications of the pre-
sent findings. As very limited research exists on whether it is
detrimental to consume energy-containing products before
sleep, the present findings begin to identify what active
people should consume in the late evening before sleep.
Conclusions
The majority of studies have compared the effects of different
proteins, macronutrients and energy loads when consumed
in the morning. The present study is the first to investigate
the effects of WP, CP, CHO and PLA when consumed before
sleep on morning satiety and resting metabolism.
We conclude that consumption of 586 to 628 kJ
(140 –150 kcal) of WP, CP and CHO before sleep increases
morning REE in healthy, physically active young men, while
that of a PLA does not. Our findings contradict the popular
belief that it is advantageous to limit energy intake in the
evening. In fact, protein consumption before sleep after an
evening resistance exercise bout has been shown to increase
muscle protein synthesis overnight in young healthy men
(17)
,
and the results of the present study suggest that regardless
of the macronutrient type, energy intake of 586– 628 kJ
(140–150 kcal) before sleep is more beneficial than not
eating. Although the aforementioned study
(17)
provided a
stimulus for muscle protein synthesis (resistance exercise),
the present results and those of Res et al.
(17)
suggest a
plausible synergistic benefit of resistance exercise and late-
evening protein consumption to increase both overnight
muscle protein synthesis and REE. Therefore, night-time pro-
tein and CHO consumption may be an effective nutritional
strategy to further enhance recovery and improve resting
metabolism with a minimal effect on the feelings of satiety.
In addition, it is convenient to hypothesise that the improve-
ment in morning resting metabolism may further aid in the
maintenance of and/or improvement in body composition
and thereby provide a competitive advantage in healthy,
physically active young men. Future studies should investigate
the impact of liquid energy intake v. solid energy intake and
combinations of the macronutrients for the most optimal meta-
bolic milieu. In addition, long-term studies of night-time feeding
are warranted.
Acknowledgements
The authors thank the participants for their dedication and
participation in the present study. The study was funded by
the Florida State University. M. J. O. conceived and designed
the study, secured funding for the project, and provided over-
sight for data collection, analysis and manuscript preparation.
T. A. M. carried out participant recruitment and data collection
and assisted with manuscript preparation. S. K. F. assisted with
data collection and recruitment. A. W. K. helped with manu-
script preparation. L. B. P. helped with the study design and
manuscript preparation. All authors read and approved the
final manuscript. None of the authors has financial or other
interests concerning the outcomes of the investigation.
The authors declare that they have no competing interests.
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