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Effects of Different Dietary Proteins and Amino Acids on Skeletal Muscle Hypertrophy in Young Adults After Resistance Exercise: A Systematic Review


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Effects of Different
Dietary Proteins and
Amino Acids on Skeletal
Muscle Hypertrophy in
Young Adults After
Resistance Exercise: A
Systematic Review
Henning Langer, BA and Anja Carlsohn, PhD
¨t Potsdam, Professur Sportmedizin und Sportorthopa
¨die, Potsdam, Germany
Investigating skeletal muscle hyper-
trophy is important for numerous
reasons. Recreational and profes-
sional athletes can benefit from hypertro-
phy as a muscle with increased cross-
sectional area (CSA) can exert more
force, eventually leading to greater
strength and power potential (39). Muscle
hypertrophy has vital implications not
only for performance but also from
a health perspective. Muscle tissue plays
a major role in regulating our metabolism
and consequentially all diseases that are
related to it (34,43). Furthermore, building
up muscle tissue in young subjects could
be a promising intervention to battle
increasingly prevalent diseases such as
sarcopenia or cachexia, which are related
to muscle loss and muscle weakness
(5,52). Starting early enough with this
could be particularly important, as
humans have been reported to become
resistant to anabolic stimuli during aging
(10,33,36,65). How to optimally stimulate
skeletal muscle hypertrophy in young
healthy adults through exercise is a con-
troversial topic (14).
Skeletal muscle hypertrophy occurs
when the aggregate of muscle protein
synthesis (MPS) exceeds the aggregate
of muscle protein breakdown (MPB)
for an extended period of time, resulting
in a positive net protein balance (NPB).
It is well-established that in order to
stimulate this process, it is essential to
overload the muscle (27,28). However,
it has been shown that in a fasted state
and without sufficient protein intake,
the anabolic effects after RE are dimin-
ished, as both MPS and MPB rise in
a similar fashion resulting in a negative
NPB (1,22,46,60).
Essential amino acids (EAAs) play a key
role, as they increase MPS and minimize
MPB, causing a higher NPB compared
with a mixture of nonessential amino
milk; whey; casein; soy; leucine; pro-
tein; resistance training; hypertrophy
Copyright ÓNational Strength and Conditioning Association Strength and Conditioning Journal | 33
acids (AAs) (60). The EAA leucine has
been suggested as a MPS key modulator
by increasing the activity of important
signaling proteins (19). Sufficient protein
intake seems to be important to maxi-
mize the contractile protein accretion
after RE, and this seems to be partially
dependent on the EAA content of the
consumed protein. A protein high in
pensable amino acid score may be
termed as a “high-quality protein” (23).
Examples of high-quality protein sources
include whey-, soy-, casein-, multicom-
ponent proteins or even AA supple-
ments such as branched-chain amino
acids (BCAA) or pure leucine. This
review will overview the effects of differ-
ent dietary proteins ingested immedi-
ately before, during, or after RE. It has
been shown that the anabolic effects of
RE differ depending on certain factors,
such as level of experience of the sub-
jects, training volume, and training inten-
sity. Therefore, the protocols of the
reviewed studies will be elucidated in
detail to allow for the results to be put
in an appropriate perspective.
A systematic PubMed database search
was performed using combinations of
the following terms: “protein ingestion,”
“casein,” “whey,” “soy,” “egg,” “beef,”
“leucine,” “amino acids,” “resistance train-
ing,” “resistance exercise,” and “weight-
lifting.” Language of the studies was
limited to English (Figure).
This review included studies that
looked at the effects of more than
one protein or AA source during their
respective experiments. The subjects in
those studies had to undergo at least 1
bout of intense RE, and indicators of
skeletal muscle hypertrophy had to be
measured before and after the inter-
vention. Examples of such indicators
are acute changes in muscle protein
turnover or long-term changes in body
composition and muscle size. All stud-
ies administered the protein in a time
frame of 90 minutes before, during, or
after RE as this seems to be crucial for
the hypertrophic response (1,22,45,53).
Studies with older (+40 years) or
diseased subjects were excluded
(Table 1).
A total of 5,868 articles were initially
found. Of this, 12 studies till July 2013
fulfilled the defined inclusion criteria
and were included in this review.
Seven studies analyzed milk proteins
(whey and casein) and their different
effects on postexercise muscle anabo-
lism or chronic changes in body com-
position. Four of them compared the
results with soy protein.
Tipton et al. (59) included 23 healthy,
young, untrained subjects of both gen-
ders. Subjects had to perform a single
bout of leg extension, consisting of 10
sets of 8 repetitions (reps) at 80% of
the 1 repetition maximum (1RM) of
the subjects, with a 2-minute break
between each set. One hour after this
bout, 20 g of whey protein (2.3 g leucine),
casein protein (1.7 g leucine), or placebo
(water) were ingested by the subjects.
Vastus lateralis biopsies were taken
55 minutes before, immediately before,
and 120 minutes and 300 minutes after
RE. Leg blood flow was measured
45–35 minutes before RE and at
40–45 minutes, 80–90 minutes, 115–
120 minutes, 200–210 minutes, and
290–300 minutes after exercise. Blood
samples were taken at 17 points from
35 minutes before exercise to 300 mi-
nutes after exercise. Appearance of AAs
(phenylalanine and leucine) in the blood
and muscle was measured, and NPB
was calculated using the following for-
mula: NPB 5(blood flow across the
leg) 3(arterial AA concentration 2
venous AA concentration).
Whey protein ingestion resulted in
a more rapid increase and larger peak
in leucine concentrations in blood and
muscle than casein ingestion, likely
because of different digestive properties
of the proteins (2,20,21). However, in
terms of the potential hypertrophy
(NPB), no significant difference between
the groups was observed. The placebo
Wilkinson et al. (64) compared a milk
protein containing drink (fat-free milk)
with an isonitrogenous and isoenergetic
soy protein drink. Eight young subjects
who were regularly engaged in RE ($4
days per week) participated in 2 bouts of
a unilateral leg workout, separated by $1
week. Three standardized exercises (leg
press, leg curl, and leg extension) were
executed, each for 4 sets at 80% of the
1RM with 2-minute rest between each
set. After the exercise, either the soy or
milk drink was ingested. Both included
18.2 g of protein, 1.5 g of fat, and 23 g of
carbohydrates (CHO). Muscle biopsies
were taken immediately before and after
180 minutes after workout. Blood sam-
ples were drawn 90 minutes before exer-
cise, directly before and after exercise,
and 30, 60, 90, 120, and 180 minutes after
RE. Blood flow was measured before
and after workout, as well as every hour
Tipton et al. (59), fractional synthesis rate
(FSR in percentage per hour) was calcu-
lated as described by Phillips et al. (46).
NPB was calculated by subtracting frac-
tional breakdown rate from FSR. The
fat-free milk stimulated FSR to a substan-
tially greater extent (34%) than the soy
drink, resulting in a significantly greater
indicates that milk proteins are a better
stimulator of postexercise muscle anab-
olism in young resistance athletes than
soy protein.
In a follow-up study by Hartman et al.,
56 college students who were previ-
ously not experienced in RE completed
a 12-week trial. Before the start of the
program, subjects were randomly as-
signed to 1 of the 3 groups (milk, soy,
or control) (29). Each subject was
trained 5 days per week on a rotating
split program. The split program con-
sisted of 3 different types of sessions,
for a total of 60 RE sessions over the
course of the 12 weeks. During the trial,
load was progressively increased (start-
ing at 80% 1RM), whereas the number of
reps per set decreased. Immediately after
each workout and again 1 hour later,
each subject consumed a drink. The
drink was either skim milk (17.5 g of
Effects of Different Dietary Proteins
VOLUME 36 | NUMBER 3 | JUNE 2014
protein, 25.7 g of CHO and 0.4 g of fat),
an isoenergetic and isonitrogenous soy
beverage, or an isoenergetic control
drink consisting of maltodextrin.
Changes in fat- and bone-free mass
measured using dual-energy x-ray ab-
sorptiometry (DEXA) and muscle biop-
sies of the vastus lateralis, respectively.
Both methods were used twice: before
the start of the RE regimen and after the
completion of the 12-week program.
The greatest gains in lean mass and
CSA could be observed in the milk pro-
tein group, followed by the soy protein
and the control groups. These findings
suggest that a combination of milk pro-
teins (i.e., whey and casein) is superior to
soy protein or CHO alone in terms of
promoting hypertrophy in young resis-
tance trained men.
Based on those findings, Candow et al.
(13) hypothesized that whey protein
would support fat-free mass gains in
young adults to a greater degree than
soy protein or an isoenergetic maltodex-
trin supplement. Twenty-seven untrained
subjects were randomly assigned into 3
groups: whey protein, soy protein, and
placebo (maltodextrin). Each participant
received a prepacked bag containing one
of the supplements. They were instructed
to ingest 1.2 g per kg bodyweight of the
supplement, 0.4 g per kg bodyweight
before and after RE, as well as before
bed. The weight training program was
composed of a 3-day rotating split, with
6–9 exercises per session and 4–5 sets per
exercise at 60–90% of their 1RM for 6–12
reps, for a total study duration of 6 weeks.
All participants had to report their die-
tary intake of 3 days during the first and
last weeks. No significant difference in
dietary habits between the groups or
weeks was observed. Mean calorie in-
takes ranged from 2,978 6702 to
3,129 6591 kcal per day and protein
intakes from 1.6 61.3 to 1.9 61.3 g
per kg bodyweight per day. However,
it is important to mention that the sup-
plementary protein intake of the whey
and soy groups was not included in these
data, meaning that most subjects were
likely to not only match but also clearly
exceed the recommended protein re-
quirements for athletes engaged in RE
(37,38,47,50). As a result of this trial,
significantly greater gains in LBM (mea-
sured by DEXA) than the placebo group.
In this study, the hypothesis that whey
Table 1
Inclusion and exclusion criteria
Criteria Included Excluded
Age ,40 y .40 y
Protein/amino acid source .1#1
Health status Healthy Diseased
Timed ingestion 690 min of RE .690 min of RE
Resistance exercise $1 bout per study No RE
Indicators of muscle
growth measured
Yes N o
Figure. Flow chart of the process of identifying and including studies for the systematic literature review.
Strength and Conditioning Journal | 35
protein would support muscle growth
to a greater extent than soy protein
could not be confirmed.
Tang et al. (56) investigated whether
there is a different effect for the isolated
proteins of milk (whey and casein) com-
pared with soy. In contrast to Tipton
et al. (59), this study found a significant
difference between casein, soy, and
whey on MPS. Eighteen young and
healthy subjects experienced in weight-
lifting (2–3 sessions per week) com-
pleted this trial. A single bout of 2
unilateral leg exercises was performed:
4 sets of leg press and leg extension at
100% of their previously determined
10–12 RM with 2-minute rest between
each set. Immediately after RE, a drink
of 21.4 g of whey, 21.9 g of casein, or
22.2 g of soy protein was ingested. Each
drink contained approximately 10 g of
EAA. A continuous L-[ring-
] phe-
nylalanine infusion, blood samples, and
muscle biopsies were used to measure
MPS at rest, after the consumption of
the drink and up to 180 minutes after
the workout. Despite similar EAA con-
tent in all drinks, the ingestion of the
whey drink resulted in a significantly
greater AUC of leucine and higher
MPS than the ingestion of soy or casein.
Therefore, whey protein seems to be
a more potent stimulator of acute mus-
cle anabolism after RE than casein or
soy. Several authors suggested that this
might be because of the faster absorp-
tion rate of whey when compared with
other proteins that are similar in EAA
content (2,20,21). However, an infusion
protocol of only 3 hours postprandially
is unlikely to catch the slow acting
effects of casein on MPS and could
therefore show an incomplete picture.
Reitelseder et al. (49) conducted
another study comparing whey with
casein. They confirmed what Tipton
et al. (59) found and could not replicate
Tang et al. (56). They had 17 subjects
not experienced in RE perform 10 sets
of 8 reps at 80% of their 1RM with 3-
minute rest between the sets. After RE,
a drink of either whey, casein (0.3 g per
kilogram lean bodyweight), or control
(non caloric) was ingested. MPS was
measured in a similar way as described
in earlier studies (46,56,59,64). Com-
pared to the study by Tang et al., the
infusion protocol of this investigation
was twice as long and assessed changes
in MPS over a 6 hour period. Whey
ingestion was followed by a greater
peak in MPS during the early phase
(1–3 hours), whereas casein caused
a higher elevation during the later phase
(3–6 hours), resulting in a similar mean
MPS over the total period (1–6 hours).
This is supporting the idea that the
slower absorption kinetics of casein re-
quires a longer infusion period to allow
for a comprehensive comparison to its
effects on MPS versus whey protein.
However, it was a special form of casein
that was used in this trial. Unlike micel-
lar casein that is found in bovine milk
and was used in the other experiments
mentioned above, this form (calcium
caseinate) has different digestive prop-
erties that are more similar to whey pro-
tein. Micellar casein is not acid soluble
causing it to be digested more slowly,
whereas caseinates are acid soluble and
release their AAs much more rapidly
into the intestine, bloodstream, and ulti-
mately peripheral tissues (18). There-
fore, the results of this study cannot
be applied to the most common form
of casein (micellar casein) and are likely
to be directly linked to this particular
form of casein (caseinate).
Recently, another comparison between
whey and casein did not show any sig-
nificant differences between changes in
body composition (63). Wilborn et al.
had 16 female basketball players partic-
ipate in this trial of 8 weeks. They par-
ticipated in 4 whole-body RE sessions
per week, which were not specified in
terms of intensity. Subjects performed 3
conditioning units per week suited
toward basketball. The subjects were
randomized into a whey or casein pro-
tein group. Both groups consumed
either an isocaloric portion of 24 g
casein or whey immediately after each
of the 7 training sessions of the week. By
the end of the 8 weeks, both groups had
increased muscle mass and strength in
a similar manner. However, the lack of
a nonprotein control group makes it
difficult to distinguish the effects of
the training protocol from the protein
Taken together, these results indicate
that a combination of milk proteins
as it is naturally occurring in bovine
milk seems to be superior to soy pro-
tein in promoting hypertrophic gains
in young healthy adults (29,56,64).
When looking at the effects of the iso-
lated milk proteins, whey protein
seems to be more facilitating in the
early phase after RE, whereas casein
ingestion results in a slower, but more
prolonged effect on MPS (49,56).
It has been suggested that the main rea-
son for soy protein being less potent in
augmenting MPS, despite its high-quality
AA profile and fast digestion rate, is the
way it is partitioned. Its AAs seem to be
primarily distributed to the splanchnic
region and less toward peripheral tissues
like muscle (3,24,57).
Results from Wilkinson and Hartman
et al. suggest that milk may be an effi-
cient postworkout nutrition and protein
source (29,64). The protein in bovine
milk as used in those studies usually
contains 20% whey to 80% casein pro-
tein (31). A combination of whey and
casein protein could be a promising
workout beverage. However, substantial
differences in absorption kinetics and
time effects of whey and casein were
observed, leaving the question whether
it is possible to ameliorate the effects of
fast- and slow-acting proteins on lean
mass accretion by combining them.
The exact role of AAs within proteins
or added to them remained unclear.
Kerksick et al. (35) compared the
effects of 3 different postworkout
drinks on body composition after 10
weeks of RE. Thirty-six subjects were
assigned to either a whey and casein
protein blend (48 g: 40 g of whey and
8 g of casein), a whey protein that was
stacked with BCAAs and glutamine
(48 g: 40 g of whey, 3 g of BCAAs +
5gofL-glutamine), or an isoenergetic
CHO placebo that had to be ingested
in a 2-hour window after RE or in the
morning (9 AM) on training-free days.
Effects of Different Dietary Proteins
VOLUME 36 | NUMBER 3 | JUNE 2014
The participants were experienced in
weightlifting and completed a 10-week
RE program (4 sessions per week), with
7–8 exercises and 21–24 sets per session,
respectively. Over the course of the
study, the training loads were progres-
sively increased, and each set throughout
the entire program was executed until
the subjects could not perform another
complete repetition. The preplanned
reps ranged from 6 to 10 per set for
most of the exercises and 25 per set
for abdominal exercises. Similarly to
Candow et al. (13), the subjects were
instructed to report their dietary habits
over a 4-day period before the start of
the trial, during weeks 2, 5, 8, and 10 of
the program. Energy intake from group
to group and week 0–10 varied between
29.2 and 39.8 kcal per kilogram body-
weight and protein intake from 1.4 to
2.5 g per kilogram bodyweight, respec-
tively. Although there was no statistical
difference between the groups, it is
important to note that every single
subject was close to matching or
even exceeding the recommended pro-
tein intake per day for RE athletes
(37,38,47,50). As a result of this trial,
significant gains in LBM measured by
DEXA occurred in the whey plus casein
group only, indicating that this protein
blend would be advantageous compared
with whey protein that wasstacked with
EAA and glutamine, which had no
effect on body composition.
In an attempt to further elaborate on
the role of leucine and EAA on MPS,
Churchward-Venne et al. (16) looked at
the effects of different whey protein dos-
ages, with or without added leucine or
EAAs. A regular dose of whey protein
(25 g) was compared with 2 different
groups of suboptimal dosages of whey
protein (6.25 g). One group had added
leucine, to match the leucine content of
the regular dosage in it and the other
had added EAAs in it, to match every
EAA of the regular dosage besides
leucine. They hypothesized that adding
leucine, but not EAA, would result in
a MPS response similar to the group
with the complete whey (19,51,60).
They had 24 subjects not experienced
in RE perform a single bout of unilateral
exercise, consisting of 4 sets of 10–12
reps leg extension and leg press at 95%
of their previously determined 1RM.
Immediately after this bout, they were
assigned to 1 of the 3 groups in a single-
blinded fashion and ingested the bever-
age. MPS was measured as described
earlier, using infusion, blood samples,
and a biopsy from the worked muscle
(vastus lateralis) (46,49,56,59,64). As
a result, they observed equal MPS
responses between the groups in the
early hours (1–3 hours) after RE, but
only the complete whey group (25 g)
was able to sustain this response for
a prolonged time (3–5 hours after exer-
cise). This implies that despite the fact
that leucine was suggested to be indis-
pensable for MPS and NPB to occur,
less of it than previously thought might
be necessary when other EAAs are
available in sufficient amounts. In addi-
tion, whey in adequate quantities seems
to be a better choice postworkout than
little amounts of protein stacked with
leucine or other EAAs. Whey in ade-
quate quantities seems to be a better
choice after workout than little
amounts of protein stacked with leucine
or other EAAs.
Reidy et al. (48) compared the effects
of whey protein with a protein blend
consisting of sodium caseinate (50%),
whey, and soy (25% each). Both bev-
erages contained approximately the
same amount of leucine (;1.8 g) and
EAAs (;8.7 g). Nineteen untrained
subjects completed a single bout of
leg exercise. They performed 8 sets of
10 reps leg extension at increasing
intensity from 55 to 70% of their
1RM with 3-minute rest between
the sets. FSR was measured using
similar methods as described in earlier
studies (16,46,49,56,59,64). The protein
drink was ingested 1 hour after RE.
Depending on the subjects’ group
and their bodyweight (0.3–0.35 g per
kilogram bodyweight), they either
received ;18 g of whey or ;19 g of
the protein blend. The group hypoth-
esized that the individual characteris-
tics of each component of the protein
blend would yield unique advantages
over whey protein. No significant
difference in MPS between the groups
could be observed in the early phase
after RE. However, as expected, the
slower kinetics of the caseinate and
the plant protein led to an increased
MPS during the late phase (2–4 hours
after RE), whereas no increase in MPS
could be observed for whey-only at that
time. This shifted effect of the slower
proteins is also reflected by differences
in the rise and fall of AA concentrations
in the serum. The authors therefore sug-
gested that a multicomponent protein
could be a better choice after RE. Sim-
ilar to the study by Reitelseder et al. (49),
it is important to consider that sodium
caseinate just like calcium caseinate does
not resemble the digestive characteris-
tics of micellar casein and instead is
absorbed much faster (18).
Herda et al. compared “bioenhanced”
whey (20 g of whey + 5 g of leucine)
with normal whey (20 g), a placebo (27
g of maltodextrin), and a control group
(30). Over 8 weeks of RE, 106 subjects,
49 of them experienced in weight train-
ing, trained 3 times per week at 80% of
their 1RM with 2-minute rest between
the sets. The subjects were randomly
assigned into 5 different groups: bioen-
hanced whey combined with a low-
volume RE program, bioenhanced
whey plus moderate volume, normal
whey plus moderate volume, placebo
plus moderate volume, and control
plus moderate volume. The different
beverages were ingested 30 minutes
before and after workout. On rest days,
they were instructed to drink it in the
morning in a postabsorptive state. Each
participant had to report 3 random days
of dietary intake (2 week days and 1
weekend day) and was asked to main-
tain his habits throughout the study.
Average kilocalorie intake between the
groups ranged from 2,320 6129 kcal to
3,029 6181 kcal. Protein intake varied
from between 0.69–1.96 g per kilogram
bodyweight (lowest average group
intake) to 1.26–2.86 g per kilogram
bodyweight (highest average group
intake), respectively. The placebo and
control groups consumed significantly
less protein than the other 3 groups.
However, even in those groups some
Strength and Conditioning Journal | 37
individuals excessively exceeded the
recommended (37,38,47,50) protein
intake per day. The changes in body
composition were evaluated using
peripheral quantitative computed tomog-
raphy. No significant changes in muscle
CSA or LBM gains could be observed
between the groups, despite the differ-
ence in total protein intake.
Recently, Joy et al. (32) compared the
effects of 48 g of rice protein versus 48
g of whey protein after RE for 8 weeks.
Subjects were 24 healthy young
males who were experienced in strength
training for at least 1 year. The RE
protocol consisted of an undulating peri-
odization program for 3 days a week.
They performed alternating whole-
body sessions at either their 8–12 RM
or 2–5 RM. The weights were increased
by 2–5% when the desired number of
reps was achieved. The authors hypoth-
esized that there would be no difference
between the groups, agreeing with
earlier assumptions about a “leucine
threshold” (4). Indeed, no significant dif-
ference between the groups was found.
Table 2
Protein sources, duration, and outcome
Reference Protein and amino acid content
of the beverages
Indicators of hypertrophy Duration Results
Tipton et al. (59) 20 g whey or 20 g casein NPB Single bout NPB[; no difference between
the groups
Wilkinson et al. (64) 18.2 g milk protein or 18.2 g soy
NPB Single bout NPB[; milk .soy
Hartman et al. (29) 17.5 milk protein or 17.5 soy
CSA, LBM 12 wk CSA[, LBM[, milk .soy
Candow et al. (13) ;30 g whey, ;30 g soy protein
or ;30 g maltodextrin
LBM 40 d LBM[; no difference between
the groups
Tang et al. (56) 21.4 g whey, 21.9 g casein, or
22.2 g soy protein
MPS Single bout MPS whey .soy .casein
Reitelseder et al.
;20 g whey or ;20 g casein MPS Single bout MPS no difference between
the groups
Wilborn et al. (63) 24 g whey or 24 g casein LBM 8 wk LBM[; no difference between
the groups
Kerksick et al. (35) 40 g whey + 8 g casein or 40 g
whey + 3 g BCAAs + 5 g
LBM 10 wk LBM[; whey plus casein .
whey plus BCAA and
et al. (16)
25 g whey, 6.25 g whey + leucine
(matched with 25 g whey),
6.25 g whey + EAA (matched
with 25g whey, besides
MPS Single bout MPS[; no difference between
the groups in the early
response; MPS remained
elevated during the late
phase only in the 25 g whey
Reidy et al. (48) ;18 g whey or ;19 g protein
blend (25% whey, 50%
sodium caseinate, 25% soy)
MPS Single bout MPS[; no differences between
the groups in the early
response; MPS remained
elevated during the late
phase only in
multicomponent protein
Herda et al. (30) 20 g whey, 20g + 5 g leucine,
27 g maltodextrin or placebo
CSA, LBM 8 wk LBM[; no difference between
the groups
Joy et al. (32) 48 g whey or 48 g rice protein LBM 8 wk LBM[; no difference between
the groups
Effects of Different Dietary Proteins
VOLUME 36 | NUMBER 3 | JUNE 2014
The rice group increased their lean mass
by 2.5 kg, which was measured using
DEXA. The whey group gained 3.2 kg
of lean mass during the intervention.
Both increased their 1RM of the per-
formed exercises in a similar manner.
The authors concluded that the study
provides evidence for the theory of
a leucine threshold. They assume that
this threshold is within the range
of 1.7–3.5 g of leucine. Similar to
Wilborn et al., this study was limited
by the lack of a control group.
Although in contrast to the majority
of the findings, the results of Herda
et al. are in line with a number of
other studies that could not find any
positive effects for protein or AA sup-
plementation combined with RE
(7,12,25,26,61,62). However, it is the
only study fulfilling the criteria of this
review that failed to show a positive
effect of protein supplementation on
indicators of skeletal muscle hyper-
trophy. There are two main reasons
that could explain these results. One
is that most subjects in the study of
RE, and it is a common observation
that novice lifters tend to respond
markedly well to the onset of RE,
unlike advanced athletes. This might
be because of a decreased MPS sig-
naling in advanced athletes, caused
by chronic loading of the muscles
(17,41,42,54). It is possible that the
beginners in the study by Herda
et al. could have benefited from their
initial sensitivity to RE, resulting in
significant hypertrophy despite sub-
optimal nutritional circumstances.
The authors agree on the chance that
the naturally high basal MPS rates in
young men, in conjunction with an
efficient RE program, could have
already been such a great stimulus
that all additional effects of protein
supplementation got whitewashed
(30). Additionally, some of the sub-
jects in each of the groups exceeded
the current recommendations for
daily protein intake by a great margin.
Potentially, this could have slightly
distorted the results despite a signifi-
cant mean difference in overall pro-
tein intake between the groups.
and calorie intake are paramount to pro-
tein ingestion with training. However,
there is no doubt that a high-quality pro-
tein source enhances acute RE-induced
MPS and NPB (16,48,49,56,59,64).
Moreover, acute NPB after exercise
and EAA ingestion reflects 24-hour
NPB (58), and there is evidence for pro-
tein to augment long-term LBM gains to
a greater degree than placebo or CHO:
A recent meta-analysis has shown that
improvements in LBM favor protein
supplementation over placebo (15). This
was regardless of the age or training sta-
tus of the subjects (15). This indicates
that studies unable to find an effect for
protein supplementation to further
enhance the effects of RE may have been
Eventually, based on the current liter-
ature, isolated or mixed milk proteins
and regular bovine milk seem to have
the most potential to facilitate muscle
growth compared with other proteins
Bovine milk is, despite its high casein
content, rapidly absorbed, resulting in
an acute MPS response that is surpris-
ingly close to isolated whey (64). The
growth-facilitating effects of milk pro-
teins seem to be greater than for other
proteins not only on the short-term but
also on the long-term in young healthy
adults (29,56,64). Furthermore, both
components of milk protein (whey
and casein) are high in leucine and
other EAAs, but only whey seems to
effectively augment acute postworkout
MPS because of its fast absorbable
characteristics (56).
In general, it appears that combining
both milk proteins, as it naturally hap-
pens in bovine milk, could be a promis-
ing strategy in further optimizing the
MPS response after RE. The fast-
acting characteristics of whey are com-
plemented by the slow-acting charac-
teristics of casein, resulting in a rapid,
but also prolonged increase in MPS
(49,64). This seems to be the case
regardless of the type of casein
(29,35,64). Adding other proteins such
as soy to those milk protein–based
blends might be advantageous as well,
but further research is needed to con-
firm the benefits of such multicompo-
nent proteins (48).
Moreover, adding leucine or other
AAs to a sufficient amount of protein,
which is already high in EAA, does
not seem to further augment skeletal
muscle hypertrophy (30,35). However,
if the amount of high-quality protein
and leucine is below what seems to be
the sufficient amount (20 g and 1–1.7 g,
respectively) (4,32,40), adding EAA or
leucine could help to still get the opti-
mal, early response after RE (16). Alter-
natively, exceeding those amounts and
consuming enough of a protein that is
poor in leucine until one transgresses
the proposed threshold of 1–1.7 g could
be feasible as well, if a protein of higher
quality is not available (32). However, if
the amount of protein is insufficient and
the shortcoming is compensated with
the addition of leucine or EAA, it would
be advisable to endorse such a compro-
mise with a full dose of a high-quality
protein shortly afterward, as only a com-
plete protein seems to allow for a pro-
longed MPS (16).
It is difficult to compare acute studies
that measured muscle protein turnover
with long-term interventions which
measured changes in muscle size. Little
is known on the long-term adaptations
of skeletal muscle to different levels of
protein intake and timing. For example,
effect sizes of muscle growth found in
long-term interventions are commonly
substantially smaller than expected
based on acute studies that measured
muscle protein turnover (30,40). Future
experiments should target the physio-
logical changes that might occur
between acute studies and long-term
interventions. For accurate recommen-
dations, further research is needed to
determine the optimal ratio of fast- to
slow-acting proteins and the role of
other AAs besides leucine. Moreover,
other high-quality protein sources such
as beef protein or egg protein have been
shown to ameliorate muscle protein
Strength and Conditioning Journal | 39
turnover to a similar degree as milk pro-
teins (40,44,55). However, to date, this
was performed exclusively in elderly,
dissociated from RE or without com-
paring it to another protein during the
same trial. Those findings are yet to be
applied to resistance trained young sub-
jects and longterm interventions.
Most of the results suggest that in-
gesting milk protein directly before
or after RE is advantageous for
individuals interested in optimizing
skeletal muscle hypertrophy. The
available literature indicates that
a combination of fast- and slow-
acting milk proteins (i.e., whey and
casein) could provide the most per-
petual anabolic effects. The exact
amount that should be ingested is
dependent on the quality of the pro-
tein and its content of EAA, specifi-
cally leucine, with 1–1.7 g of leucine
appearing to be optimal to facilitate
muscle protein accretion in young
subjects. Approximately 20 g of a milk
protein followed by a similar amount
;1 hour later, or alternatively ;40 g
in a single bolus feeding seem to be
sufficient to maximize the acute MPS
response after RE, as well as long-
term hypertrophy. Exceeding those
amounts might be necessary only if
a protein of lower quality (i.e.,
plant-based protein) is chosen. Par-
ticularly, individuals with low protein
intake and protein sources of poor
quality could benefit from protein
supplementation around training.
Conflicts of Interest and Source of Funding:
The authors report no conflicts of interest
and no source of funding.
Henning Langer
is a graduate
student (MSc
program, Biology
of Human Perfor-
mance and
Health) at Maas-
tricht University
Anja Carlsohn is
an Assistant
Professor at the
University of
The authors thank Fabian Ottawa for
his assistance in revising the article.
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Effects of Different Dietary Proteins
VOLUME 36 | NUMBER 3 | JUNE 2014
... Previous systematic reviews have attempted to distinguish the effects of different protein sources on muscle health outcomes including muscle mass and strength (Appendix 3). However, to our knowledge, previous reviews have not extended the scope to include important physical performance or sarcopenia outcomes for the ageing muscle [26][27][28]. Furthermore, reviews have been limited either by the sole inclusion of younger adults (< 40 years) [26] or by focusing primarily on soy plant proteins [27] rather than the comprehensive range of plant proteins that have been studied. ...
... However, to our knowledge, previous reviews have not extended the scope to include important physical performance or sarcopenia outcomes for the ageing muscle [26][27][28]. Furthermore, reviews have been limited either by the sole inclusion of younger adults (< 40 years) [26] or by focusing primarily on soy plant proteins [27] rather than the comprehensive range of plant proteins that have been studied. Previous reviews also did not consider the effects of sex in analyses, yet there may be important sex differences in the impact of different protein sources on muscle health. ...
Full-text available
Background The evidence base for the role of dietary protein in maintaining good muscle health in older age is strong; however, the importance of protein source remains unclear. Plant proteins are generally of lower quality, with a less favourable amino acid profile and reduced bioavailability; therefore, it is possible that their therapeutic effects may be less than that of higher quality animal proteins. This review aims to evaluate the effectiveness of plant and animal protein interventions on muscle health outcomes. Methods A robust search strategy was developed to include terms relating to dietary protein with a focus on protein source, for example dairy, meat and soy. These were linked to terms related to muscle health outcomes, for example mass, strength, performance and sarcopenia. Five databases will be searched: MEDLINE, Scopus, Cochrane Central Register of Controlled Trials, Embase and Web of Science. Studies included will be randomised controlled trials with an adult population (≥ 18) living in the community or residential homes for older adults, and only English language articles will be included. Two independent reviewers will assess eligibility of individual studies. The internal validity of included studies will be assessed using Cochrane Risk of Bias 2.0 tool. Results will be synthesised in narrative format. Where applicable, standardised mean differences (SMD) (95% confidence interval [CI]) will be combined using a random-effects meta-analysis, and tests of homogeneity of variance will be calculated. Discussion Dietary guidelines recommend a change towards a plant-based diet that is more sustainable for health and for the environment; however, reduction of animal-based foods may impact protein quality in the diet. High-quality protein is important for maintenance of muscle health in older age; therefore, there is a need to understand whether replacement of animal protein with plant protein will make a significant difference in terms of muscle health outcomes. Findings from this review will be informative for sustainable nutritional guidelines, particularly for older adults and for those following vegan or vegetarian diets. Systematic review registration PROSPERO CRD420201886582
... The effects of animal protein vs. plant protein on muscle mass and strength have been examined in a few systematic reviews, but there are research gaps. One publication concluded that a higher amount of plant protein is needed to achieve muscle growth similar to animal protein [20]. However, the review included trials which only studied acute changes in muscle protein turnover. ...
Full-text available
Although animal protein is usually considered to be a more potent stimulator of muscle protein synthesis than plant protein, the effect of protein source on lean mass and muscle strength needs to be systematically reviewed. This study aimed to examine potential differences in the effect of animal vs. plant protein on lean mass and muscle strength, and the possible influence of resistance exercise training (RET) and age. The following databases were searched: PubMed, Embase, Scopus and CINAHL Plus with Full Text, and 3081 articles were screened. A total of 18 articles were selected for systematic review, of which, 16 were used for meta-analysis. Total protein intakes were generally above the recommended dietary allowance at the baseline and end of intervention. Results from the meta-analyses demonstrated that protein source did not affect changes in absolute lean mass or muscle strength. However, there was a favoring effect of animal protein on percent lean mass. RET had no influence on the results, while younger adults (<50 years) were found to gain absolute and percent lean mass with animal protein intake (weighted mean difference (WMD), 0.41 kg; 95% confidence interval (CI) 0.08 to 0.74; WMD 0.50%; 95% CI 0.00 to 1.01). Collectively, animal protein tends to be more beneficial for lean mass than plant protein, especially in younger adults.
... Consumption of adequate levels of leucine (1-1.7g) which is found in sufficient levels in whey and casein proteins is necessary for maximal muscle protein accretion. 26 Consumption of carbohydrates and amino acids independently have positive effects on post exercise recovery but when consumed together may provide synergistically greater benefits than either macronutrient consumed alone. 15,23,27 These additive effects may be attributed to increased release of insulin, increased glycogen re-synthesis, increased protein synthesis and a reduction in protein breakdown. ...
Full-text available
The purposes of this dissertation were to examine the effect of a protein and carbohydrate recovery beverage versus a placebo on weightlifting performance, its effect on muscle morphological changes and specific muscle protein accretion. The following are major finding from the dissertation: 1) Protein and carbohydrate recovery supplementation does not appear to have influence on performance measure in trained weightlifters. This finding may be associated with the short-term nature of this study and the trained population used. 2) Compared with placebo, a protein and carbohydrate beverage provided greater benefits on cross sectional area of type I and type II muscle fibers. Additionally, the block periodization protocol incorporating phase potentiation improved cross sectional area of both groups compared to baseline. 3) Finally, protein and carbohydrate supplementation provided greater benefits on total mTOR and myosin heavy chains 6 & 7. These findings indicate that a protein and carbohydrate beverage provide greater benefits compared with a placebo on cellular signaling, myosin heavy gene expression and muscle fiber increases in trained weightlifters. Improved cross sectional area and increased myosin heavy chains indicate positive adaptations to resistance training combined with supplementation and may indicate improved skeletal muscle qualities necessary for increased power output. The mTOR pathway is the master regulator of cellular growth and increases in total mTOR indicate a greater proclivity for cellular growth and greater activity resulting from resistance training may increase synthesis and accretion of muscle contractile proteins. This dissertation highlighted several benefits of recovery supplementation, however further longitudinal studies utilizing block periodization and well-trained athletes are necessary to fully elucidate benefits for strength and power athletes.
Full-text available
About the Book: This book compiled with quality research papers of the Two Day International E-Conference on “Trends Issues and Development of Physical Education and Sports” under the theme of “All round development of human personality” jointly organised by Department of Physical Education and Sports Science, Fit India Campaign Committee and Fit India Club, Manipur University, Canchipur in collaboration with National Association of Physical Education and Sports Science (NAPESS). This book has been undertaken by the organisers to share the knowledge of the professionals through their research papers and to exchange their experience and research finding area in the field of physical educational and sports science. This is the book of the reviews on the concrete solutions to the permanent problems in the physical education and sports science. It is a humble energy to bind the drowning talents of physical education and sports. We express our gratitude, to those humble physical education teachers, research scholars, students, sports lovers, coaches, and sports administrators, who made this chance. Editor Dr. L.Santosh Singh
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Background: Resistance exercise leads to net muscle protein accretion through a synergistic interaction of exercise and feeding. Proteins from different sources may differ in their ability to support muscle protein accretion because of different patterns of postprandial hyperaminoacidemia. Objective: We examined the effect of consuming isonitrogenous, isoenergetic, and macronutrient-matched soy or milk beverages (18 g protein, 750 kJ) on protein kinetics and net muscle protein balance after resistance exercise in healthy young men. Our hypothesis was that soy ingestion would result in larger but transient hyperaminoacidemia compared with milk and that milk would promote a greater net balance because of lower but prolonged hyperaminoacidemia. Design: Arterial-venous amino acid balance and muscle fractional synthesis rates were measured in young men who consumed fluid milk or a soy-protein beverage in a crossover design after a bout of resistance exercise. Results: Ingestion of both soy and milk resulted in a positive net protein balance. Analysis of area under the net balance curves indicated an overall greater net balance after milk ingestion (P < 0.05). The fractional synthesis rate in muscle was also greater after milk consumption (0.10 ± 0.01%/h) than after soy consumption (0.07 ± 0.01%/h; P = 0.05). Conclusions: Milk-based proteins promote muscle protein accretion to a greater extent than do soy-based proteins when consumed after resistance exercise. The consumption of either milk or soy protein with resistance training promotes muscle mass maintenance and gains, but chronic consumption of milk proteins after resistance exercise likely supports a more rapid lean mass accrual.
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Protein intake that exceeds the recommended daily allowance is widely accepted for both endurance and power athletes. However, considering the variety of proteins that are available much less is known concerning the benefits of consuming one protein versus another. The purpose of this paper is to identify and analyze key factors in order to make responsible recommendations to both the general and athletic populations. Evaluation of a protein is fundamental in determining its appropriateness in the human diet. Proteins that are of inferior content and digestibility are important to recognize and restrict or limit in the diet. Similarly, such knowledge will provide an ability to identify proteins that provide the greatest benefit and should be consumed. The various techniques utilized to rate protein will be discussed. Traditionally, sources of dietary protein are seen as either being of animal or vegetable origin. Animal sources provide a complete source of protein (i.e. containing all essential amino acids), whereas vegetable sources generally lack one or more of the essential amino acids. Animal sources of dietary protein, despite providing a complete protein and numerous vitamins and minerals, have some health professionals concerned about the amount of saturated fat common in these foods compared to vegetable sources. The advent of processing techniques has shifted some of this attention and ignited the sports supplement marketplace with derivative products such as whey, casein and soy. Individually, these products vary in quality and applicability to certain populations. The benefits that these particular proteins possess are discussed. In addition, the impact that elevated protein consumption has on health and safety issues (i.e. bone health, renal function) are also reviewed.
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Two of the most popular forms of protein on the market are whey and casein. Both proteins are derived from milk but each protein differs in absorption rate and bioavailability, thus it is possible that each type of protein may contribute differently to the adaptations elicited through resistance training. Therefore, the purpose of this study was to investigate the potential effects of ingestion of two types of protein in conjunction with a controlled resistance training program in collegiate female basketball players. Sixteen NCAA Division III female basketball players were matched according to body mass and randomly assigned in a double-blind manner to consume 24 g whey protein (WP) (N = 8, 20.0 ± 1.9 years, 1.58 ± 0.27 m, 66. 0 ± 4.9 kg, 27.0 ± 4.9 %BF) or 24 g casein protein (CP) (N = 8, 21.0 ± 2.8 years, 1.53 ± 0.29 m, 68.0 ± 2.9 kg, 25.0 ± 5.7 %BF) immediately pre- and post-exercise for eight weeks. Subjects participated in a supervised 4-day per week undulating periodized training program. At 0 and 8 weeks, subjects underwent DXA body composition analysis, and at 0 and 8 weeks underwent one repetition maximum (1RM) strength, muscle endurance, vertical jump, 5-10-5 agility run, and broad jump testing sessions. Data were analyzed using repeated measures ANOVA, and presented as mean ± SD changes from baseline after 60 days. No significant group x time interaction effects were observed among groups in changes in any variable (p > 0.05). A significant time effect was observed for body fat (WP: -2.0 ± 1.1 %BF; CP: -1.0 ± 1.6 %BF, p < 0.001), lean mass (WP: 1.5 ± 1.0 kg; CP: 1. 4 ± 1.0 kg, p < 0.001), fat mass (WP: -1.3 ± 1.2 kg; CP: -0.6 ± 1.4 kg, p < 0.001), leg press 1RM (WP: 88.7 ± 43.9 kg; CP: 90.0 ± 48.5 kg, p < 0.001), bench press 1RM (WP: 7.5 ± 4.6 kg; CP: 4.3 ± 4.5 kg, p = 0.01), vertical jump (WP: 4.1 ± 1.8 cm; CP: 3.5 ± 7.6 cm, p < 0.001), 5-10-5 (WP: -0.3 ± 0.2 sec; CP: -0.09 ± 0.42 sec, p < 0.001), and broad jump (WP: 10.4 ± 6.6 cm; CP: 12. 9 ± 7.1 cm, p < 0.001). The combination of a controlled undulating resistance training program with pre- and post-exercise protein supplementation is capable of inducing significant changes in performance and body composition. There does not appear to be a difference in the performance- enhancing effects between whey and casein proteins. Key pointsFemales can experience and increase in performance makers from consuming protein after resistance training.Females can have a decreased body fat composition when ingesting protein with daily resistance training and conditioning.There was no significant difference in performance markers between whey and casein.
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Emulsions prepared using casein micelles and sodium caseinate as the emulsifying agent are compared. It is found that the ultrastructure of the casein proteins influences the properties of the emulsion.
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Background Consumption of moderate amounts of animal-derived protein has been shown to differently influence skeletal muscle hypertrophy during resistance training when compared with nitrogenous and isoenergetic amounts of plant-based protein administered in small to moderate doses. Therefore, the purpose of the study was to determine if the post-exercise consumption of rice protein isolate could increase recovery and elicit adequate changes in body composition compared to equally dosed whey protein isolate if given in large, isocaloric doses. Methods 24 college-aged, resistance trained males were recruited for this study. Subjects were randomly and equally divided into two groups, either consuming 48 g of rice or whey protein isolate (isocaloric and isonitrogenous) on training days. Subjects trained 3 days per week for 8 weeks as a part of a daily undulating periodized resistance-training program. The rice and whey protein supplements were consumed immediately following exercise. Ratings of perceived recovery, soreness, and readiness to train were recorded prior to and following the first training session. Ultrasonography determined muscle thickness, dual emission x-ray absorptiometry determined body composition, and bench press and leg press for upper and lower body strength were recorded during weeks 0, 4, and 8. An ANOVA model was used to measure group, time, and group by time interactions. If any main effects were observed, a Tukey post-hoc was employed to locate where differences occurred. Results No detectable differences were present in psychometric scores of perceived recovery, soreness, or readiness to train (p > 0.05). Significant time effects were observed in which lean body mass, muscle mass, strength and power all increased and fat mass decreased; however, no condition by time interactions were observed (p > 0.05). Conclusion Both whey and rice protein isolate administration post resistance exercise improved indices of body composition and exercise performance; however, there were no differences between the two groups.
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In February 2002, the American College of Sports Medicine (ACSM) published a Position Stand entitled Progression Models in Resistance Training for Healthy Adults. The ACSM claims that the programmed manipulation of resistance-training protocols such as the training modality, repetition duration, range of repetitions, number of sets, and frequency of training will differentially affect specific physiological adaptations such as muscular strength, hypertrophy, power, and endurance. The ACSM also asserts that for progression in healthy adults, the programs for intermediate, advanced, and elite trainees must be different from those prescribed for novices. An objective evaluation of the resistance-training studies shows that these claims are primarily unsubstantiated. In fact, the preponderance of resistance-training studies suggest that simple, low-volume, time-efficient, resistance training is just as effective for increasing muscular strength, hypertrophy, power, and endurance - regardless of training experience - as are the complex, high-volume, time-consuming protocols that are recommended in the Position Stand. This document examines the basis for many of the claims in the Position Stand and provides an objective review of the resistance training literature.
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Background: Older individuals generally experience a reduced food-chewing efficiency. As a consequence, food texture may represent an important factor that modulates dietary protein digestion and absorption kinetics and the subsequent postprandial protein balance. Objective: We assessed the effect of meat texture on the dietary protein digestion rate, amino acid availability, and subsequent postprandial protein balance in vivo in older men. Design: Ten older men (mean ± SEM age: 74 ± 2 y) were randomly assigned to a crossover experiment that involved 2 treatments in which they consumed 135 g of specifically produced intrinsically L-[1-(13)C]phenylalanine-labeled beef, which was provided as beef steak or minced beef. Meat consumption was combined with continuous intravenous L-[ring-(2)H5]phenylalanine and L-[ring-(2)H2]tyrosine infusion to assess beef protein digestion and absorption kinetics as well as whole-body protein balance and skeletal muscle protein synthesis rates. Results: Meat protein-derived phenylalanine appeared more rapidly in the circulation after minced beef than after beef steak consumption (P < 0.05). Also, its availability in the circulation during the 6-h postprandial period was greater after minced beef than after beef steak consumption (61 ± 3% compared with 49 ± 3%, respectively; P < 0.01). The whole-body protein balance was more positive after minced beef than after beef steak consumption (29 ± 2 compared with 19 ± 3 μmol phenylalanine/kg, respectively; P < 0.01). Skeletal muscle protein synthesis rates did not differ between treatments when assessed over a 6-h postprandial period. Conclusions: Minced beef is more rapidly digested and absorbed than beef steak, which results in increased amino acid availability and greater postprandial protein retention. However, this does not result in greater postprandial muscle protein synthesis rates. This trial was registered at as NCT01145131.
Skeletal muscle is the largest organ in the body. Skeletal muscles are primarily characterized by their mechanical activity required for posture, movement, and breathing, which depends on muscle fiber contractions. However, skeletal muscle is not just a component in our locomotor system. Recent evidence has identified skeletal muscle as a secretory organ. We have suggested that cytokines and other peptides that are produced, expressed, and released by muscle fibers and exert either autocrine, paracrine, or endocrine effects should be classified as "myokines." The muscle secretome consists of several hundred secreted peptides. This finding provides a conceptual basis and a whole new paradigm for understanding how muscles communicate with other organs such as adipose tissue, liver, pancreas, bones, and brain. In addition, several myokines exert their effects within the muscle itself. Many proteins produced by skeletal muscle are dependent upon contraction. Therefore, it is likely that myokines may contribute in the mediation of the health benefits of exercise. © 2013 American Physiological Society. Compr Physiol 3:1337-1362, 2013.