Whey protein consumption after resistance exercise reduces energy intake at a post-exercise meal

Abstract

Purpose:
Protein consumption after resistance exercise potentiates muscle protein synthesis, but its effects on subsequent appetite in this context are unknown. This study examined appetite and energy intake following consumption of protein- and carbohydrate-containing drinks after resistance exercise.

Methods:
After familiarisation, 15 resistance training males (age 21 ± 1 years, body mass 78.0 ± 11.9 kg, stature 1.78 ± 0.07 m) completed two randomised, double-blind trials, consisting of lower-body resistance exercise, followed by consumption of a whey protein (PRO 23.9 ± 3.6 g protein) or dextrose (CHO 26.5 ± 3.8 g carbohydrate) drink in the 5 min post-exercise. An ad libitum meal was served 60 min later, with subjective appetite measured throughout. Drinks were flavoured and matched for energy content and volume. The PRO drink provided 0.3 g/kg body mass protein.

Results:
Ad libitum energy intake (PRO 3742 ± 994 kJ; CHO 4172 ± 1132 kJ; P = 0.007) and mean eating rate (PRO 339 ± 102 kJ/min; CHO 405 ± 154 kJ/min; P = 0.009) were lower during PRO. The change in eating rate was associated with the change in energy intake (R = 0.661, P = 0.007). No interaction effects were observed for subjective measures of appetite. The PRO drink was perceived as creamier and thicker, and less pleasant, sweet and refreshing (P < 0.05).

Conclusion:
These results suggest whey protein consumption after resistance exercise reduces subsequent energy intake, and this might be partially mediated by a reduced eating rate. Whilst this reduced energy intake is unlikely to impair hypertrophy, it may be of value in supporting an energy deficit for weight loss.

Full text

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Eur J Nutr (2018) 57:585–592
https://doi.org/10.1007/s00394-016-1344-4
ORIGINAL CONTRIBUTION
Whey protein consumption after resistance exercise reduces
energy intake at a post‑exercise meal
Alistair Monteyne1 · Alex Martin1 · Liam Jackson1 · Nick Corrigan1 · Ellen Stringer1 ·
Jack Newey1 · Penny L. S. Rumbold2 · Emma J. Stevenson3 · Lewis J. James1
Received: 28 July 2016 / Accepted: 29 October 2016 / Published online: 10 November 2016
© The Author(s) 2016. This article is published with open access at Springerlink.com
observed for subjective measures of appetite. The PRO
drink was perceived as creamier and thicker, and less pleas-
ant, sweet and refreshing (P < 0.05).
Conclusion These results suggest whey protein consump-
tion after resistance exercise reduces subsequent energy
intake, and this might be partially mediated by a reduced
eating rate. Whilst this reduced energy intake is unlikely
to impair hypertrophy, it may be of value in supporting an
energy deficit for weight loss.
Keywords Appetite · Energy balance · Weight
management · Protein synthesis · Anabolism · Body
composition
Introduction
Muscle hypertrophy is highly desirable to a wide range
of populations, ranging from those seeking optimal ath-
letic performance, to those seeking to maintain functional
capacity for health. Concurrently, resistance exercise is also
recommended as part of a holistic model for weight man-
agement [1]. Resistance exercise and post-exercise protein
feeding synergistically potentiate muscle protein synthe-
sis, orchestrating muscle fibre hypertrophy [2]. At least
in young, resistance-trained men, whey protein has been
shown to stimulate muscle protein synthesis to a greater
extent than other proteins when doses of 20–25 g protein
are ingested [3], with this amount of whey protein being
sufficient to maximise this response after lower limb resist-
ance exercise [4].
Protein has been suggested to be the most satiating
macronutrient, and protein feeding at rest has been shown
to reduce subsequent energy intake compared to other
macronutrients [5], and protein-containing drinks have
Abstract
Purpose Protein consumption after resistance exercise
potentiates muscle protein synthesis, but its effects on sub-
sequent appetite in this context are unknown. This study
examined appetite and energy intake following consump-
tion of protein- and carbohydrate-containing drinks after
resistance exercise.
Methods After familiarisation, 15 resistance training
males (age 21 ± 1 years, body mass 78.0 ± 11.9 kg, stat-
ure 1.78 ± 0.07 m) completed two randomised, double-
blind trials, consisting of lower-body resistance exer-
cise, followed by consumption of a whey protein (PRO
23.9 ± 3.6 g protein) or dextrose (CHO 26.5 ± 3.8 g car-
bohydrate) drink in the 5 min post-exercise. An ad libitum
meal was served 60 min later, with subjective appetite
measured throughout. Drinks were flavoured and matched
for energy content and volume. The PRO drink provided
0.3 g/kg body mass protein.
Results Ad libitum energy intake (PRO 3742 ± 994 kJ;
CHO 4172 ± 1132 kJ; P = 0.007) and mean eating
rate (PRO 339 ± 102 kJ/min; CHO 405 ± 154 kJ/min;
P = 0.009) were lower during PRO. The change in eat-
ing rate was associated with the change in energy intake
(R = 0.661, P = 0.007). No interaction effects were
* Lewis J. James
L.James@lboro.ac.uk
1 School of Sport, Exercise and Health Sciences,
Loughborough University, Leicestershire LE11 3TU, UK
2 Department of Sport, Exercise and Rehabilitation, Faculty
of Health and Life Sciences, Northumbria University,
Newcastle upon Tyne NE1 8ST, UK
3 Institute of Cellular Medicine, Human Nutrition Research
Centre, Newcastle University, Newcastle upon Tyne NE2
4HH, UK
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586 Eur J Nutr (2018) 57:585–592
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been shown to attenuate energy intake at a subsequent
meal in a dose-dependent manner [6]. Therefore, if post-
exercise protein intake reduces subsequent energy intake
sufficiently, this might reduce the anabolic response to sub-
sequent protein intake, which is potentiated for some time
after exercise [7].
Whilst resistance exercise in isolation has been shown
to alter appetite regulation, to date, very few studies have
considered the interaction of exercise and post-exercise
nutrition on subsequent appetite and energy intake. This is
particularly important for resistance exercise where post-
exercise protein intake is recommended to maximise the
anabolic response [2]. When consumed after aerobic exer-
cise, Clayton et al. [8] observed no significant difference
in subsequent energy intake between energy-matched whey
protein and carbohydrate drinks. It is feasible, however,
that resistance exercise may interact with liquid protein to
elicit a dissimilar response to aerobic exercise; a premise
that has yet to be investigated.
Therefore, the purpose of this study was to compare
drinks containing dextrose (i.e. carbohydrate) and whey
protein consumed after resistance exercise on subsequent
appetite and energy intake. It was hypothesised that the
whey protein drink would suppress appetite and reduce
energy intake relative to the carbohydrate drink.
Methods
Subjects
After approval by the Loughborough University Eth-
ics Approvals (Human Participants) Sub-Committee, 15
physically active, healthy males, who included resist-
ance exercise in their exercise routine (age 21 ± 1 years,
body mass 78 ± 11.9 kg, stature 1.78 ± 0.07 m, BMI
24.6 ± 2.6 kg m−2) provided consent and completed this
study. Subjects were not restrained, disinhibited or hungry
eaters [9]. Subjects performed a familiarisation trial and
two experimental trials, with the experimental trials being
administered in a randomised double-blind manner and
separated by ≥5 days. Using previous data from our labo-
ratory for the main outcome variable (i.e. ad libitum energy
intake), an a priori sample size calculation with statistical
power of 0.95 and α of 0.05 estimated 15 subjects would
be required to reject the null hypothesis if there was a mean
difference of 400 kJ between trials.
Familiarisation trial
Subject’s stature and mass were recorded and skinfold
measurements were made at four sites (biceps, triceps,
subscapular and suprailiac) to estimate body fat using the
Siri equation [10]. Subjects then completed a 5-min warm-
up on a friction-braked cycle ergometer (Monark828E,
Varberg, Sweden), at a standardised work rate (1.5–2 W/
kg body mass). One repetition maximum (1RM) was
then determined for unilateral leg extension and leg flex-
ion (Technogym Element + Leg Extension and Leg Curl,
Technogym U.K. Ltd, Berkshire, UK). A successful repeti-
tion was judged by subjects producing an acceptably full
range of motion. Subjects rested as required between 1RM
attempts. Subjects then completed two sets of 10 reps at
70% of 1RM (Table 1) to familiarise them with the resist-
ance training protocol used in the experimental trials, after
which they were familiarised with the ad libitum pasta
meal described later.
Pre‑trial standardisation
Subjects completed a food and activity diary in the 24 h
preceding the first experimental trial and were asked to
replicate this in the 24 h before their second trial. Atypi-
cal dietary habits, alcohol ingestion and strenuous physi-
cal activity were not permitted in this period. All subjects
consumed a standardised breakfast two h before exercise
commenced, providing 15% of estimated energy require-
ments (RMR [11] multiplied by a physical activity level of
1.7) and 1 g/kg body mass of carbohydrate. The breakfast
was consumed in the subject’s home and consisted of semi-
skimmed milk (Tesco, Cheshunt, UK) and Nutri-Grain bars
(Kelloggs, Manchester, UK) in a ratio of 125-ml milk 30 g
Nutri-Grain. Compliance with these pre-trial requirements
was verbally confirmed prior to each trial.
Experimental trials
Participants arrived at the testing facility between 10:00
and 11:00 (standardised within subjects), and post-void
body mass in minimal clothing was measured. Subjects
completed approximately 50 min of resistance exercise and
then immediately ingested either a protein (PRO) or car-
bohydrate (CHO) drink. This was followed by a period of
60-min rest in a comfortable environment. The ad libitum
meal was served 65 min after the end of exercise, and sub-
jects were allowed 20 min in which to eat. Questionnaires
assessing subjective appetite were collected at regular inter-
vals throughout, along with a drink characteristic question-
naire that was collected after post-exercise drink ingestion.
Resistance exercise
Subjects completed the standardised 5-min warm-up
described for the familiarisation trial, followed by 2-min
rest. Resistance exercise was unilateral extension of the
right and left leg, followed by unilateral flexion of the
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587Eur J Nutr (2018) 57:585–592
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right and left leg. For each exercise on each leg subjects
completed one warm-up set of 10 repetitions at 35% 1RM
and four working sets of 10 reps at 70% 1RM. If subjects
fatigued before they had completed four sets of 10 reps
during the first experimental trial, they replicated this work
in the second trial. In the second trial, all subjects were able
to replicate work done from the first trial. Two minutes
rest was allowed between each set. Subjects were provided
with water ad libitum up until the start of the final exercise
(i.e. left leg flexion) during the first trial, with this amount
matched during the second trial.
Ad libitum meal
Subjects were seated in an eating booth to isolate them
from external stimuli as much as possible. The test
meal consisted of pasta (400 g dry-weight), Bolognese
sauce (400 g), and olive oil (32 g) (Tesco, Cheshunt,
UK). The meal was homogenous in nature and provided
5.84 ± 0.04 kJ/g (12% protein, 69% carbohydrate, 19%
fat). Subjects were initially provided with a portion con-
taining just over half of the total food prepared. A new por-
tion, containing the remainder of the prepared food, was
provided part way through the protocol at a time specific to
the subjects eating rate. This was to ensure that finishing a
bowl did not act as a satiety cue. Subjects were instructed
to “eat until comfortably full and satisfied”, at which point
they moved from the eating booth to a chair inside the eat-
ing laboratory. A period of 20 min was allocated to eat the
test meal and subjects remained in the eating laboratory
for the entire time. The time spent eating was recorded and
together with the total energy intake was used to determine
the mean eating rate. Water was available ad libitum during
the meal. The meal was served in two large pasta bowls and
warmed before serving. All meals were subject to identical
preparation, cooking, heating and serving protocols. Food
and water intake were measured by weighing bowls and
glasses before and after consumption, with energy intake
quantified from manufacturer values.
Post‑exercise drink
Subjects were provided with a dextrose monohydrate
drink (Myprotein, Manchester, UK) in the CHO trial, and
a whey protein isolate drink (WPI90, Volac International
Ltd., Orwell, UK) in the PRO trial. (Table 2) The protein
drink provided 0.3 g protein/kg body mass, in line with
current guidelines [2]. The carbohydrate drink was isoen-
ergetic in comparison with the protein drink, although a
little over 0.3 g carbohydrate/kg body mass was provided
due the small additional fat and lactose content of the whey
protein isolate. Manufacturer values were used to deter-
mine the macronutrient and energy content of powders.
The powder for each drink was assimilated in 400 ml of
no added sugar orange squash (Tesco Stores Ltd., Ches-
hunt, UK) and the subjects consumed this 400 ml. An addi-
tional 100 ml squash was then added to the bottle, mixed
with any remaining residue and consumed by the subjects.
Subjects were given 5 min to consume the drink. The drink
was served in an opaque sports bottle and was consumed
through a sports cap to reduce sensory and textural cues.
The drink was provided in a randomised, double-blind
manner. Drinks were prepared on the same day as the trial,
earlier that morning. Subjects were aware that the study
was investigating the appetite effects of post-resistance
exercise drink composition, but were unaware of the com-
position of drinks.
At the end of the study, subjects were told that the drinks
consumed were a carbohydrate drink and a whey protein
drink and were asked if they could identify which drink
they had ingested on which trial.
Subjective appetite questionnaire
Subjects rated their perceptions of appetite via 100-mm
visual analogue scales (VAS) [12]. Questions asked were
related to hunger “How hungry do you feel?”; fullness
“How full do you feel?”; desire to eat (DTE) “How strong
is your desire to eat?” and prospective food consumption
(PFC) “How much food do you think you could eat?”,
with verbal anchors “not at all”/“none at all” at 0 mm
and “extremely”/“a lot” at 100 mm. Subjects completed
this questionnaire pre-exercise, post-exercise, post-drink,
15 min post-drink, 30 min post-drink, 45 min post-drink,
60 min post-drink and at the end of the test meal. Total area
under the curve (AUC) values were calculated for subjec-
tive appetite responses in the period between drink con-
sumption and the ad libitum meal (i.e. post-drink to 60 min
post-drink).
Drink characteristics questionnaire
Additional 100-mm VAS questions were assessed immedi-
ately after drink consumption. Questions asked were “How
pleasant was the drink?”, “How much aftertaste did the
drink have?”, “How salty was the drink?”, “How bitter was
the drink?”, “How sweet was the drink?”, “How creamy
was the drink?”, “How thick was the drink?”, “How sticky
was the drink?”, “How fruity was the drink?” and “How
refreshing was the drink?”. Verbal anchors “not at all” and
“extremely/extreme” were placed at 0 mm and 100 mm,
respectively.
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588 Eur J Nutr (2018) 57:585–592
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Data analysis
Data were analysed using SPSS 22 (SPSS Inc., Somers,
NY, USA). All data were examined for normality of distri-
bution using a Shapiro–Wilk test. Normally distributed data
containing one factor were analysed using paired samples
t tests, and non-normally distributed data containing one
factor were analysed using Wilcoxon signed-rank tests.
Data containing two factors were analysed using a two-
way repeated measures ANOVA. Statistical significance
was set at P < 0.05. Data are presented as mean ± standard
deviation.
Results
Pre‑trial measurements
There was no difference between trials for pre-trial
body mass (PRO 78.9 ± 12.4 kg; CHO 78.7 ± 12.4 kg;
P = 0.437), or subjective sensations of hunger (PRO
40 ± 20 mm; CHO 40 ± 18 mm; P = 0.978), fullness
(PRO 51 ± 12 mm; CHO 47 ± 15 mm; P = 0.347), DTE
(PRO 40 ± 23 mm; CHO 43 ± 21 mm; P = 0.193) or PFC
(PRO 46 ± 21 mm; CHO 51 ± 19 mm; P = 0.282).
Ad libitum meal
Energy intake at the ad libitum meal was reduced during
PRO compared to CHO (P = 0.009; Fig. 1). Eating rate was
also reduced during PRO compared to CHO (P = 0.011;
Fig. 2). The change in eating rate between trials was asso-
ciated with the change in energy intake between trials
(r = 0.662, P = 0.007) Fig. 3. Ad libitum water intake
did not differ between trials (P = 0.691) and amounted to
339 ± 146 ml during PRO and 349 ± 152 ml during CHO.
There was no trial order effect for energy intake (trial 1
3874 ± 924 kJ; trial 2 4040 ± 1224 kJ; P = 0.599) or eating
rate (trial 1 373 ± 90 kJ; trial 2 371 ± 168 kJ; P = 0.689).
Drink perception
Subjects perceived PRO to be thicker (P = 0.001) and
creamier (P = 0.001) than CHO, whilst CHO was
Table 1 One repetition
maximum (1RM) and weight
lifted during the working sets
(kg) during the resistance
exercise in experimental trials
Data are mean ± SD
Right leg extension Left leg extension Right leg flexion Left leg flexion
1RM (kg) 60.7 ± 16.0 60.3 ± 17.0 41.5 ± 9.4 41.5 ± 10.0
Working weight (kg) 42.2 ± 10.4 42 ± 11.3 28.7 ± 5.5 28.7 ± 6.3
Table 2 Composition of post-exercise drinks
Data are mean ± SD
Protein (PRO) Carbohydrate (CHO)
Volume (ml) 500 500
Energy (kJ) 459 ± 64 459 ± 64
Protein (g) 23.9 ± 3.6 0.4 ± 0.0
Carbohydrate (g) 2.7 ± 0.1 26.5 ± 3.8
Fat (g) 0.1 ± 0.0 0.0 ± 0.0
Fibre (g) 0.4 ± 0.0 0.4 ± 0.0
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
PRO CHO
Energy Intake (kJ)
†
Fig. 1 Energy intake at the ad libitum test meal (kJ). Dagger (†)
significantly different from CHO (P = 0.009). Bars are mean ± SD,
with lines representing individual subject data
200
300
400
500
600
700
800
900
PRO CHO
Eang Rate (kJ/min)
†
Fig. 2 Mean eating rate at the ad libitum test meal (kJ min−1).
Dagger (†) significantly different from CHO (P = 0.011). Bars are
mean ± SD, with lines representing individual subject data
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589Eur J Nutr (2018) 57:585–592
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perceived as being more pleasant (P = 0.014), sweeter
(P = 0.004) and more refreshing (P = 0.028) than PRO.
There was no difference between drinks for any other char-
acteristics (P > 0.250, Fig. 4).
Subjective appetite ratings
There was a main effect of time for all subjective appetite
measures (hunger P = 0.001; fullness P = 0.001; DTE
P = 0.001; PFC P = 0.001), but no main effects of trial
(hunger P = 0.301; fullness P = 0.671; DTE P = 0.150;
PFC P = 0.051) or interaction effect (hunger P = 0.559;
fullness P = 0.442; DTE P = 0.163; PFC P = 0.302).
AUC values in response to the drinks were not different
between trials for any subjective appetite variable (hun-
ger P = 0.425; fullness P = 0.512; DTE P = 0.234; PFC
P = 0.220) (Table 3).
Detection of study drinks
At the end of the study when subjects were told the drinks
used in the study were a carbohydrate drink and a whey
protein drink, 11 of the 15 subjects correctly identified on
which trial they had consumed which drink.
Fig. 3 Change in eating rate
(kJ min−1) versus change in
energy intake (kJ) during the
ad libitum meal (r = 0.662,
P = 0.007)
-300
-250
-200
-150
-100
-50
0
50
100
-2000-1500 -1000-500 0
500
Difference in Eang Rate vs CHO (kJ/min)
Difference in Energy Intake vs CHO (kJ)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
Pleasant AertasteSalty BierSweet Creamy ThickScky Fruity Refreshing
Drink Percepon (mm)
Drink Characteriscs
††
††
†
Fig. 4 Subjective perceptions of test drinks (mm); PRO (black square) and CHO (grey square). Dagger (†) Significantly different from CHO
(P < 0.05). Bars are mean ± SD
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590 Eur J Nutr (2018) 57:585–592
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Discussion
The aim of this study was to examine the effect of the macro-
nutrient composition of a drink consumed after resistance
exercise on subsequent appetite and ad libitum energy intake.
The primary finding was that energy intake was reduced after
the consumption of a whey protein isolate drink compared to
an energy-matched carbohydrate drink. Mean eating rate was
also reduced after consumption of the whey protein drink. Fur-
thermore, there were significant differences in drink character-
istics, with the whey protein drink being perceived as thicker
and creamier, as well as less sweet, pleasant and refreshing,
which might have influenced subsequent energy intake.
It has been suggested that the daily discrepancy between
intake and expenditure causing long-term weight gain is
slight [13, 14]. Accordingly, the modest reduction in energy
intake observed in the current study (430 ± 579 kJ) may
augment the effects of resistance exercise in aiding long-
term weight management. The coefficient of variation of a
single-item ad libitum meal with prior dietary standardisa-
tion has been shown to be ~8.9% [15]. The mean difference
in energy intake between trials in the present study equated
to 10.3%, which was slightly greater than that reported
by Gregersen et al. [15], although the reproducibility of
the ad libitum meal in the present study might have been
improved by the inclusion of a familiarisation trial to habit-
uate subjects to the meal and eating environment. Resist-
ance exercise increases acute energy expenditure [16] and
the resultant increase in muscle mass [17] might increase
daily energy requirements via alterations in basal metabolic
rate. The present study suggests that a reduction in energy
intake following resistance exercise with whey protein
consumption may offer an additional mechanism through
which body re-composition might occur.
Several plausible explanations exist as to why protein
in drink form might be more satiating than carbohydrate.
These include effects on: gastrointestinal appetite-related
hormones; circulating amino acids; and the sensory pro-
file of the drink. Protein consumption has been shown to
elevate peripheral concentrations of the anorexogenic hor-
mones CCK and GLP-1 to a greater extent than carbohy-
drate, resulting in greater satiety [18, 19], although the
strength of this relationship remains unclear. Additionally,
the hyperaminoacidemia that occurs following protein
ingestion may affect appetite both directly through amino
acid-mediated mechanisms and indirectly by influencing
glucose homeostasis [20]. These blood-based measure-
ments were not made in the present study, representing a
limitation that should be rectified in future studies. Whilst
energy intake was reduced during the PRO trial, there was
no difference between trials for any subjective appetite
measures. Some [6, 19, 21, 22], but not all [18, 23] previ-
ous studies at rest have reported enhanced satiety after con-
suming protein-containing drinks, but perhaps the inclusion
of resistance exercise in the present study, which alters sub-
jective appetite responses independently [16] accounts for
the lack of difference observed. In line with this hypothesis,
no difference in subjective appetite has been observed fol-
lowing manipulation of the carbohydrate and protein con-
tent of drinks consumed after endurance exercise [8, 24],
which also independently alters subjective appetite [16].
The greater thickness and creaminess of the protein drink
may have played a role in reducing energy intake. The sen-
sory characteristics of a drink modify its satiating properties
and might influence subsequent energy intake [25]. Viscos-
ity, or thickness, seems to play a particularly important role,
with thicker drinks enhancing expectations of satiety [26,
27]. Within the literature that has noted differences in energy
intake between drinks of differing macronutrient content, it
is not uncommon for drinks to either differ in hedonic quali-
ties or for subjects to clearly identify differences between
drinks in terms of texture or flavour [6, 21, 23, 24]. Berten-
shaw et al. [28] demonstrated that matching high protein and
carbohydrate drinks for perceived thickness and creaminess
resulted in very similar satiety responses, despite liquid pro-
tein typically being found to induce greater satiety elsewhere
in the literature. Furthermore, protein drinks that were less
thick and creamy, despite being matched for nutritional
content, were found to be less satiating, resulting in greater
ad libitum energy intake compared to a sensory-enhanced
protein drink. These results suggest that the sensory charac-
teristics of drinks are critical in determining short-term sati-
ety [28]. The exact mechanisms by which orosensory char-
acteristics of drinks influence appetite and energy intake are
not clear, although such factors have been shown to elicit a
hormonal effect associated with appetite control [29].
Within the current study, the protein drink was perceived
to be thicker and creamier than the carbohydrate drink, and
less pleasant. Consequently, it is probable that orosensory
factors may have played a causal role in the reduction in
energy intake after consumption of the protein drink com-
pared to the carbohydrate drink. Clayton et al. [8] reported
energy intake 60 min after consuming whey protein and
carbohydrate drinks was not different, whilst Rumbold
et al. [24] reported reduced energy intake 60 min after
Table 3 Total area under curve for subjective appetite ratings
Data are mean ± SD
DTE desire to eat, PFC prospective food consumption
Subjective appetite measure PRO CHO
Hunger (mm/60 min) 3466 ± 955 3632 ± 813
Fullness (mm/60 min) 2148 ± 921 1982 ± 724
DTE (mm/60 min) 3515 ± 1042 3756 ± 755
PFC (mm/60 min) 3676 ± 906 3922 ± 636
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591Eur J Nutr (2018) 57:585–592
1 3
consuming skimmed milk compared to a carbohydrate
drink. Interestingly, Clayton et al. [8] did not observe dif-
ferences in the thickness or creaminess of the drinks, a find-
ing that is likely due to the nature of the whey protein used
and the fact that drinks were consumed through a straw to
limit orosensory exposure. Whilst Rumbold et al. [24] did
not report the subjects sensory perceptions of the drinks,
the nature of the drinks (milk vs. orange juice) means it is
highly likely that sensory differences, particularly thickness
and creaminess would have been present [23]. Collectively,
these results suggest that similar to consumption at rest
[28], the orosensory effects of drinks consumed after exer-
cise might be important for how a drink impacts ad libi-
tum energy intake. Whilst the failure to match drinks for
orosensory factors might represent a limitation of the pre-
sent study, it also increases the external validity of the study
as in practice protein and carbohydrate drinks consumed in
a post-exercise setting would likely differ hedonically.
The results of the present study suggest that the reduc-
tion in energy intake after protein consumption appears
to be at least partially mediated by a reduction in eating
rate. Mean eating rate was reduced after protein consump-
tion, and the change in eating rate was associated with the
change in energy intake. Empirical evidence suggests that
manipulating eating rate affects energy intake, with slower
eating rates reducing energy intake [30]. Furthermore,
reductions in energy intake as a result of slowed eating
rates are not associated with increased hunger, decreasing
the risk of subsequent compensatory eating [31]. In evalu-
ation, consuming a protein drink after resistance exercise
may be an effective behavioural strategy to modify subse-
quent eating rate, which in turn might reduce energy intake
without deleterious effects on hunger.
Resistance exercise increases muscle protein synthesis
[32], and protein feeding post-exercise further potentiates this
response [33], whilst concurrently suppressing muscle pro-
tein breakdown [34]. The synergistically stimulated increase
in muscle protein synthesis, and to a lesser extent decrease in
muscle protein breakdown, permits positive net protein bal-
ance and consequent muscle fibre hypertrophy [17]. Whilst
the impact on hypertrophy of the reduction in energy intake
observed in the present study is unknown, it seems unlikely
it would significantly impair the process. Longland et al. [35]
restricted energy intake by ~40% during a 4-week resistance
training period whilst providing protein equivalent to 1.2 and
2.4 g/kg body mass in two separate groups, respectively. Over
the 4-week training period both groups lost ~3.5 kg of body
mass, but there was no change in lean mass in a group con-
suming 1.2 g/kg protein and a ~1.2 kg increase in lean mass
in a group consuming 2.4 g/kg protein. This suggests lean
mass can be augmented whilst in negative energy balance,
providing a high protein intake and resistance exercise are in
place, at least in non-resistance-trained males. The reduction
in energy intake after the whey protein drink in the present
study equates to ~3% of subject’s estimated daily energy
requirements. Given the findings of Longland et al. [35],
the small reduction in energy intake observed after the whey
protein beverage in the present study is unlikely to adversely
affect the augmentation of lean mass.
The proximity of the ad libitum meal to the post-exer-
cise drink is relatively close within the current investiga-
tion, and it would be interesting to see whether the reduc-
tion in energy intake would remain at a more distal time
point. The average time interval for voluntary meal requests
has been suggested to occur ~80 min after the termination
of exercise [36], which is similar to the 65 min used in the
present study. Furthermore, the present study only exam-
ined a single post-exercise meal and as such future inves-
tigations should track energy intake responses over longer
periods, as well as including measurements of other com-
ponents of energy balance (i.e. resting and physical activ-
ity energy expenditure). Finally, as the subjects used in the
present study were experienced with resistance exercise,
these results might not translate to those at the start of a
resistance training programme.
To conclude, when a whey protein isolate drink was con-
sumed after resistance exercise in lean men experienced
with resistance exercise, in an amount known to maximise
muscle protein synthesis, there was a reduction in subse-
quent energy intake at a single ad libitum meal compared
to an energy-matched carbohydrate drink. The reduction in
energy intake was modest (430 kJ), and may have been par-
tially mediated by a reduction in eating rate, as well as the
sensory characteristics of the drink. Whilst this reduction
in energy intake is unlikely to impair the energy provision
required to optimise muscle hypertrophy, it may be benefi-
cial for those individuals seeking to reduce body fat.
Acknowledgements The authors would like to thank Volac Interna-
tional Ltd for providing the whey protein isolate used in this study.
Compliance with ethical standards
Conflict of interest LJJ has previously received funding from Volac
International, which was in no way linked to the present study. LJJ
has previously received honoraria from the dairy industry for presenta-
tions given at meetings/conferences. PLSR and EJS have previously
received funding from the dairy industry for their research, which was
in no way linked to the present study. EJS has previously received
honoraria from the dairy industry for presentations given at meetings/
conferences.
Open Access This article is distributed under the terms of the Crea-
tive Commons Attribution 4.0 International License (http://crea-
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

592 Eur J Nutr (2018) 57:585–592
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