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Whey is one of the high-quality sources of protein with a higher proportion of indispensable amino acids (IAA) compared to other sources. Its high leucine concentration makes whey an optimal protein source to maximize muscle protein synthesis (MPS) and to attenuate muscle protein breakdown at rest and following exercise. This review describes the main characteristics of the currently commercialized whey protein products and summarizes the available scientific evidence on the use of whey protein supplementation to maximize muscle mass gain in young adults without considering the impact on strength performance. Results of studies conducted in humans to date indicate that the integration of whey protein in the diet of resistance-trained individuals is effective in order to maximize muscle mass accretion. Nonetheless, the observed improvements are minimized when the total daily protein intake reaches a minimum of  1.6 g/kg. Under resting conditions, a single serving of ~0.24 g/kg body mass seems to be enough for stimulating a maximal postprandial response of MPS. Although this amount is effective to significantly promote an anabolic response after exercise, higher single doses of protein >0.40 g/kg after high volume workouts, involving large muscle mass, along with a minimum daily protein intake of >1.6 g/kg have been proposed as optimal to maximally stimulate MPS. Additionally, it seems that consuming whey protein as a part of a multi-ingredient admixture composed of carbohydrate, other protein sources and creatine monohydrate is more beneficial in order to maximize muscle mass gain in young resistance trained individuals. These recommendations need to be confirmed by studies analyzing the MPS response to different workout configurations using a variety of intensities, training volumes (low, moderate or high) and the amount of the exercised muscle mass.
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REVIEW
Whey protein supplementation and muscle mass:
current perspectives
This article was published in the following Dove Press journal:
Nutrition and Dietary Supplements
Fernando Naclerio
Marcos Seijo
School of Human Sciences, Department
of Sport Science and Physical Education,
University of Greenwich, London, UK
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Abstract: Whey is one of the high-quality sources of protein with a higher proportion of
indispensable amino acids compared to other sources. Its high leucine concentration makes
whey an optimal protein source to maximize muscle protein synthesis (MPS) and to attenuate
muscle protein breakdown at rest and following exercise. This review describes the main
characteristics of the currently commercialized whey protein products and summarizes the
available scientic evidence on the use of whey protein supplementation to maximize muscle
mass gain in young adults without considering the impact on strength performance. Results
of studies conducted on humans to date indicate that the integration of whey protein in the
diet of resistance-trained individuals is effective in order to maximize muscle mass acces-
sion. Nonetheless, the observed improvements are minimized when the total daily protein
intake reaches a minimum of 1.6 g/kg. Under resting conditions, a single serving of ~0.24
g/kg body mass seems to be enough for stimulating a maximal postprandial response of
MPS. Although this amount is effective to signicantly promote an anabolic response after
exercise, higher single doses of protein >0.40 g/kg after high volume workouts, involving
large muscle mass, along with a minimum daily protein intake of >1.6 g/kg have been
proposed as optimal to maximally stimulate MPS. Additionally, it seems that consuming
whey protein as a part of a multi-ingredient admixture composed of carbohydrate, other
protein sources and creatine monohydrate is more benecial in order to maximize muscle
mass gain in young resistance-trained individuals. These recommendations need to be
conrmed by studies analyzing the MPS response to different workout congurations
using a variety of intensities, training volumes (low, moderate or high) and the amount of
the exercised muscle mass.
Keywords: indispensable amino acids, leucine, hypertrophy, nutrition, lean mass
Introduction
Whey protein has been proposed as an optimal protein source for supporting muscle
mass accretion in humans.
1,2
In comparison to other protein sources, whey protein
has greater bioavailability, solubility and concentration of branched-chain amino
acid (BCAA), particularly leucine.
3
Findings from well-conducted meta-analyses of
randomized controlled trials support the effect of combining whey protein supple-
mentation with resistance training to optimize muscle mass accretion in trained
2
and non-trained
4,5
individuals. Additionally, a more inclusive (49 studies with 1863
participants) meta-analysis by Morton et al
6
supported the effect of protein supple-
mentation to augment fat-free mass accretion by 27% (~0.3 kg) on average when
combined with resistance training programs lasting for ~6 weeks. This gure is
smaller than the 0.7 kg reported by Cermak et al
4
or the 1.3 kg determined by
Naclerio and Larumbe-Zabala.
2
Nonetheless, the improvements reported by
Correspondence: Fernando Naclerio
University of Greenwich, Avery Hill
Campus, Sparrows Farm, Sparrows Lane,
Eltham, London SE9 2BT, UK
Tel +44 020 831 8441
Fax +44 020831 9805
Email f.j.naclerio@gre.ac.uk
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Cermak et al
4
and Morton et al
6
resulted from a general
analysis, merging trained and untrained, younger and older
participants. When data from these two studies are ana-
lyzed using subgroups differentiated by the training status,
the impact of protein supplementation on lean mass gain
increased by +1.05 kg
6
and +0.98 kg.
4
These results are
very similar to those reported by Naclerio and Larumbe-
Zabala
2
who only used young resistance-trained
individuals.
Despite the available evidence supporting the benets
of protein supplementation, mainly from whey, to max-
imize muscle mass gain, there are still some controversial
results
7,8
questioning the effectiveness of using protein for
supporting muscle mass accretion in recreationally trained
participants. It is likely that some uncontrolled factors,
such as the type and quality of the protein source, the
protocol of ingestion, including the dose per singular
intake, timing of ingestion, eating patterns, including
meal frequency and macronutrient distribution, the co-
ingestion of other nutrients, and the energy content of the
daily diet could have caused discrepancies between stu-
dies. In addition, the inuence of the participantstraining
status and the training program conguration (volume,
intensity and exercise selection) represent two of the
most relevant variables to be considered to correctly inter-
pret the observed results.
9
In this short review, after
describing the main characteristics of the currently com-
mercialized whey protein products, the effectiveness of
whey protein supplementation to maximize muscle mass
gain in young adults, without considering the impact on
strength performance will be analyzed.
An exhaustive literature review, considering solely human
intervention studies, was performed until 31 December 2018
by using PubMed, Science Direct, Web of Science and Google
Scholar. Combinations of the following keywords were used as
search terms: whey protein supplementationAND resis-
tance exerciseOR resistance trainingOR strength exer-
ciseOR strength trainingOR weight liftingAND
muscular hypertrophyOR muscle massOR fat free
massOR lean body massAND humans. After an initial
screening of title and abstracts, selected manuscripts were
examined, including the reference lists of the retrieved articles.
The inclusion criteria for this short narrative review were the
following: 1) randomized controlled trial studies using trained
and untrained young adults (aged 18 years up to 45 years); 2)
the participants were classied as healthy with no medical
contraindications; 3) the participants were assessed under rest-
ing or post-resistance exercise conditions in the fed or fasted
state; 4) trials should involve at least two groups or conditions
(eg, treatment and control) to analyze the acute or long-term
effects (>4 weeks) of whey protein supplementation, adminis-
tered alone or as a part of multi-ingredient vs calorie equivalent
contrast supplement (eg, carbohydrates). There were no restric-
tions on the number of participants, nor for sex, sports disci-
pline or level of performance. Studies where participants were
classied as patients, eg, unhealthy, including overweight or
obese or any non-human intervention, were excluded.
The primary outcome variables were lean body mass, fat-
free mass, muscle protein synthesis response, muscle protein
balance, muscle hypertrophy and muscular thickness.
Finally, we also considered results and studies included in
previous protein supplementation reviews.
2,46,10
The conducted search resulted in the assessment of 28
intervention studies for this narrative review. Of these, 15
were focused on the effect of whey protein supplementa-
tion to acutely enhance muscle protein synthesis (MPS)
response and 13 examined the effect of whey protein to
promote superior muscle mass accretion after a training
period of >4 weeks.
Whey protein supplement types
There are several types of whey protein supplements on
the market. The most common are 1) whey protein con-
centrate (WPC), 2) whey protein isolate (WPI) and 3)
whey protein hydrolysate (WPH).
Protein concentrates are produced by the coagulation
of milk with the enzyme rennet or acid, resulting in the
separation of curds and whey. Further ultraltration and
drying produces WPCs containing more than 25% up to
~90% of pure protein.
11
Additional processes such as
selective elution, or ion exchange chromatography can be
used to further produce a more pure and fractionated whey
isolate product containing 90% of pure protein with very
low amounts of lactose and lipids.
12,13
In both WPC and
WPI, a mixture of native intact protein is available.
Subsequent hydrolysis with enzymes or acids provides a
way to breakdown the structure of protein contained in
WPC and WPI,
14
producing WPH mainly composed of di
and tripeptides, with higher bioavailability and more rapid
absorption time compared to intact protein products.
15
Although current manufacturing techniques for produ-
cing WPC and WPI can preserve the native structure of
whey protein, some fractions may change their concentra-
tion, increasing or decreasing the resulted proportion in the
nal whey product. In general, WPI could present a
slightly reduced concentration of glycomacropeptides,
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lactoferrin, lactoperoxidase and some bioactive peptides.
Nonetheless, cross-ow microltration using low tempera-
tures and not exposed to uctuating pH changes, produces
a WPI retaining a very similar proportion of nature whey
protein sub-fractions with trace amounts of fat and
lactose.
13
The main advantage of ion exchanges hydrolysates
products is their rapid uptake and availability of amino
acids (AAs) and a possible strong insulinotropic effect that
would elicit a fast and powerful stimulus on MPS during
the postprandial period.
16
This advantageous postprandial
effect of WPH may contribute to optimizing the muscle
anabolic response during exercise conditions,
17
and pro-
vide potential cardio-protective effects associated with a
reduced postprandial lipemia.
18
Native whey protein is a relatively new whey product
obtained by ltration of unprocessed raw milk.
19,20
Native
whey differs from the typical WPC and WPI by not con-
taining glycomacropeptides and maintaining a higher leu-
cine content with respect to the more common WPC or
WPI.
20
In addition to the typical WPC or WPI that are very
sensitive to the effect of ultra-high temperature (UHT),
which may result in protein denaturation, aggregation
and occulation, a microparticulated form of whey protein
concentrate (mWPC) is also available.
21
Microparticulation is an advanced processing technology
that is typically achieved by thermal aggregation and acid
precipitation combined with high shear conditions.
22
This
treatment can improve heat stability aggregation and gela-
tion in consumer products in which UHT processing is
required.
21
Although mWPC has increased stability and a
lower pH,
23
no difference to improve MPS was observed 1
hr after consuming 20 g of mWPC or WPC, providing
similar leucine concentrations in physically active healthy
young men that were ingesting both supplements with
water in resting conditions.
Whey protein quality: bioavailability
and AA prole
Nutritionally essential or indispensable amino acids
(IAAs) are dened as either those AAs whose carbon
skeletons cannot be synthesized or those that are inade-
quately synthesized de novo by the body relative to needs,
and which must be provided from the diet to meet optimal
requirements.
24,25
Non-essential or dispensable AAs are
those which can be synthesized de novo in adequate
amounts by the body to meet optimal requirements.
24,25
Dietary protein sources are considered complete when
they provide all IAA. In general, many vegetable foods
lack or contain very low amounts of one or more IAA,
called a limiting AA, and therefore are termed incomplete
protein foods.
11
BasedonthedigestibleIAAscore(DIAAS)
methodology,
26
animal protein including whey, casein, egg
or beef contains a higher amount and proportion of
IAAcompared with vegetable protein sources, such as soy,
potato, cereals or wheat.
26
Moreover, certain plant-based pro-
teins (eg, cereals) are limited in IAA such as lysine, threonine
and tryptophan, whereas others (eg, legumes) are limited in
cysteine and methionine. Therefore, whereas the DIAAS for
milk, eggs and beef are well above 100%, plant-derived pro-
teins generally score well below 80%. Nonetheless, some
protein extracts obtained from soy,
27
rice
28
or pea
29
have
demonstrated scores closer or above 100%. Figure 1 indicates
that when the same amount of protein is consumed, whey
isolate extracts provide more IAA, including leucine, com-
pared with other animal (casein, egg, beef, insect or bovine
colostrum) and plant (hemp, pea, brown rice) protein products.
With the DIAAS, protein quality is determined based on
the ideal AA requirement pattern and the true ileal digest-
ibility of each IAA as assessed in humans, growing pigs or
growing rats.
26
In humans, the reference ideal protein
source was established based on the AA requirement pat-
tern for different age ranges: 00.5; 12, 310; 1114; 15
18 and >18 years old.
26
Even though the ideal protein
should cover all of the known requirements for the IAA in
each of the age ranges, the overall requirements of 310-
year-old children have been considered for adolescents and
adults.
26,30
Furthermore, it is important to highlight that as
currently dened, the pattern of IAA requirements reects
the minimum level of required intake of each IAA that,
although it may be slightly overestimated,
31
should not be
considered to represent an optimal or even a maximum level
of IAA intake.
3
The scoring pattern for protein quality is determined by
calculating the ratio of each IAA established requirement to
the protein need and expressed as mg of AA provided per g
of the analyzed protein.
26
Thus, the criteria to determine
both the IAA and protein requirements, inuences the mag-
nitude of each AA within the scoring pattern and conse-
quently the extent to which the pattern would identify a food
protein source as adequate or decient in one or more
IAA.
32
Overall, a good quality protein source for adults
has been dened as one that meets at least 100% of all
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IAA requirements if 0.66 g/kg/day of this protein source is
ingested.
26
Considering leucine as the key trigger IAA that turns
on MPS
33
in situations like exercise-induced muscle mass
gain, where MPS is the variable to maximize, it would be
more important to focus on the leucine availability rather
than the total IAA content.
3
Thus, reaching a certain
amount of leucine (leucine threshold) is an important
aspect to consider in determining the potential effect of a
given protein-rich food for further stimulating muscle
mass accretion. For instance, in adults consuming 0.66 g/
kg/d of protein which, as previously stated, is the lowest
daily protein intake required to maintain body protein
mass, a minimum amount of 0.039 g/kg/d of leucine
needs to be absorbed through the ileum.
26
The requirement
of 0.039 mg/kg of leucine in adults represents the highest
value of any IAA.
31
In order to satisfy the minimum
demand of leucine requirement, the ingested protein
source should provide an average of 0.059 mg/g of diges-
tible leucine.
26
When the AA prole of the ideal protein source is used to
calculate the DIAAS, it is possible to establish the AA
reference ratio (AARR) dened as the digestible content
of a given IAA in the protein measured, compared to a
hypothetical best protein that provides the necessary amount
of all IAA.
3
Based on a rat model, and the AA requirement
pattern of a 0.53-year-old child, Rutherfurd et al
30
calcu-
lated the AARR of all the IAA in several animal and plant
100
90
80
70
60
Grams per 100 g of protein
50
40
30
20
10
0
WPI WEC BC Hydrobeef Insect IP
IAA
Leucine
Hemp C P1 S1 BRC100% All
beef
CC
Figure 1 Amino acid prole of different protein sources describing the proportion of indispensable amino acids (IAA) and leucine in different animals and plant protein
sources. Modied from: Phillips SM. The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass. Nutr Metab. 2016;13:64.
doi:10.1186/s12986-0160124-8.;
3
Naclerio F, Seijo-Bujia M, Larumbe-Zabala E, Earnest CP. Carbohydrates Alone or Mixing with Beef or Whey Protein Promote Similar
Training Outcomes in Resistance Training Males: A Double-Blind, Randomized Controlled Clinical Trial. Int J Sport Nutr Exerc Metab. 2017;27(5):408420.;
77
Churchward-
Venne TA, Pinckaers PJM, van Loon JJA, van Loon LJC. Consideration of insects as a source of dietary protein for human consumption. Nutr Rev. 2017;75(12):10351045.
78
Abbreviations: WPI, whey protein isolate from the raw matter Optipep; CC, calcium caseinate; WEC, whole egg concentrate; BC, bovine colostrum; 100% All Beef,
Hydrolysed Beef Protein from Crown Sport Nutrition (Spain) Hydrolysed Meat Protein from the raw matter Hydrobeef; Insect IP, insect isolate protein reported aminogram
from Churchward-Venne et al; Hemp C, hemp protein concentrate; PI, pea isolate protein; SI, soy isolate protein; BRC, brown rice concentrate.
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protein sources. Only milk protein concentrates and whey
isolate extracts reached values higher than 1 (100%) in all the
IAA. Furthermore, the AARR of leucine was higher in milk
(1.77) and whey (isolate, 2.57 and concentrate, 1.93) com-
pared to two sources of soy protein isolate (1.13 and 1.29)
pea protein isolate (1.37) and rice protein concentrate (1.11).
In certain circumstances, such as regular exercise training,
some protein sources may be more appropriate to satisfy
physiological demands. For example, an increased consump-
tion of whey protein containing foods providing higher levels
of leucine, compared to those suggested by the DIAAS, may
be useful to optimize training adaptation in athletes
34
or
overcoming the normal resistance to the anabolic effect
observed in the elderly.
35
Effects of whey protein to maximize
muscle gains in young resistance-
trained individuals
Several researchers have studied the effectiveness of com-
bining whey protein supplementation with resistance train-
ing to maximize muscle mass accretion in young trained
individuals.
1,2,36
The advantages of using whey protein to
maximize muscle mass gains in trained participants have
been proposed after observing acute signicant increases
in the MPS response (recognized as a primary determinant
of exercise-nutrition induced muscle hypertrophy)
6
follow-
ing a single exercise bout, or by analyzing whether the
addition of whey protein vs a contrast isoenergic supple-
ment (eg, maltodextrin) elicits superior outcomes over an
intervention period (eg, 6, 12, 24 weeks or 1 year). In this
section, a summary of the most relevant available litera-
ture regarding the effect of whey protein supplementation
to 1) acutely enhance MPS response or 2) to promote
superior hypertrophy outcomes after a minimum interven-
tion period of 4 weeks will be presented.
Studies analyzing the acute dose
response effect of combining whey
protein with resistance exercise to
stimulate MPS
In the post-absorptive state, an acute bout of resistance exer-
cise stimulates MPS by more than 100% above basal levels.
However, as there is a concomitant proportional larger activa-
tion of the muscle protein breakdown, the net protein balance
remains negative.
37
Only when protein is ingested in conjunc-
tion with workouts a synergistic effect will be obtained to
create a meaningful increase in MPS leading to a positive
net protein balance.
38
Therefore, the summative effects of
many bouts of resistance exercise in combination with protein
intake will promote muscle protein accretion over time.
39
The
effective dose of ingested AAs/protein for stimulating a max-
imal resting postprandial response of MPS has been very well
analyzed
34,40
and eventually established in 0.24 g/kg body
mass per serving in young adults
41
achieving a minimum
daily intake of ~0.8 g/kg of protein to potentially maintain
muscle mass in resting conditions.
42
Nonetheless, in young
resistance training individuals aiming to gain muscle mass,
higher single dose of protein ~0.40 g/kg
43
along with a mini-
mum daily protein intake >1.6
6
to ~2.0 g/kg
44
have been
recently suggested as the optimal amount for the post-workout
intake.
44
Within this context, during exercise recovery condi-
tions the effective doses to maximally stimulate MPS still
remain undened and may be inuenced by the type of
ingested protein source.
10
The presence of a relatively high
proportion of IAA including leucine has been considered one
of the most relevant factors affecting the concomitant post-
prandial MPS response during the post-exercise recovery
period.
3
Indeed, a dose-dependent relationship between the
amount of IAA ingested from different protein sources and
MPS has been observed.
40,45,46
Whey protein has proven to be
the best high-quality, rapidly digestible source of IAA to
maximize MPS rates at rest and during the initial several
hours of recovery following exercises.
47
Nonetheless, when
other plant-based sources with lower proportion of IAA are
ingested, larger amount of proteins with a concomitant
increased nitrogen, energy intake, longer digestion time, oxi-
dation and ureagenesis,
42,48
may be needed to compensate for
the less efcient anabolic stimulus.
49
Tang et al
46
reported signicant post-exercise MPS
increases after consuming 10 g of whey protein combined
with 21 g of fructose, in young well resistance-trained men.
Considering that whey protein provides ~50% of IAA
50
and
1112% of leucine,
51
in a 10 g dose of whey, ~5 g of IAA and
~1 to 1.2 g of leucine are provided. The participants analyzed
by Tang et al had a body mass of ~80 kg and consequently they
were ingesting ~0.12 g/kg of protein including ~0.062 g/kg of
IAA and ~0.012 to 0.015 g/kg of leucine. Despite the fact that
this amount of protein falls slightly below the accepted doses
(0.180.30 g/kg) to optimally stimulate MPS in young
individuals
43
it can be considered a minimal threshold amount
to increase MPS in the early post-exercise conditions. In this
regard, Churchward-Venne et al
52
reported that a suboptimal
dose (6.5 g) of whey protein enriched either with leucine
(containing a total of 8.4 g of protein, 5.1 g of IAA and 3 g
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of leucine), or a mixture of all IAAwithout leucine (containing
atotalof12.5gofprotein,9.3gofIAAand0.75gofleucine),
similarly stimulated MPS with respect to the ingestion of 25 g
of WPI (providing a total of 11.5 g of IAA and 3 g of leucine)
under resting conditions, and for the rst 3 hrs after an acute
bout of unilateral resistance exercise in young resistance train-
ing males. However, only ingesting 25 g of complete whey
sustained exercise-induced rates of MPS for more than 35hrs
post-workout and may be more appropriate to obtain a more
optimal post-exercise anabolic response. It is worth noting that
the average body mass ±2 standard deviation of the participants
used by Churchward-Venne et al was 76.4±4.0 kg. Therefore,
the participants ingesting the suboptimal enriched admixtures
were always consuming >0.10 g/kg of protein, providing
>0.060 g/kg of IAA and ~0.010 g/kg of leucine. These gures
could represent a minimum effective, albeit not optimal, single
serving dose of protein, IAA and leucine, respectively, to
signicantly enhance MPS in young individuals at rest, or
during the early (up to 3 hrs) post-workout period. In support
of the previous rationale, and although using a different aged
population (3855 years old), Mitchell et al (2017)
53
observed
signicant increases in the mammalian target of rapamycin C1
(mTORC1) pathway by the ingestion of only 9.2 g of milk
protein providing ~0.12 g/kg of protein, 0.052 g/kg of IAA and
~0.011 g/kg of leucine in non-resistance-trained men after
performing four sets of unliteral leg extension and leg press.
Taken together, it seems that at rest and during the early
post-exercise recovery period, a minimum amount (>0.10 g/
kg) of high-quality protein (eg, whey), providing ~0.060 g/kg
of IAA and ~0.010 g/kg of leucine are necessary to signi-
cantly increase MPS. Nonetheless, a higher amount of ~0.24 g/
kg of high-quality protein, including >0.10 g/kg of IAA and
>0.010 g/kg of leucine will be needed to maximally stimulate
MPS at rest.
As previously highlighted, under exercise conditions
requirements increase, and although a minimal effective dose
can enhance MPS compared to baseline, further increases of
MPS can be much benecial for maximizing training out-
comes. In this regard, the impact of the workout conguration,
particularly the volume
54
and the amount of exercised muscle
mass
55
has shown to be crucial in altering the dynamics of the
MPS response to protein feeding during the post-exercise
time.
56
Witard et al
40
reported optimal MPS responses mea-
sured over ~4 hrs after performing eight sets of ten repetitions
of two unilateral lower body exercises and ingesting 20 g of
WPI containing ~10 g of IAA and ~2.2 g of leucine. It is worth
highlighting that a dose of 40 g providing ~20 g of IAA and 4.4
g of leucine resulted in negligible, non-signicant stimulation
of MPS. When the relative dose (g of protein per kg of body
mass) is analyzed, the participants allocated to the 20 g serving
consumed ~0.24 g/kg of protein, 0.12 g of IAA and 0.026 g/kg
of leucine, while those who consumed 40 g were receiving
~0.50g/kgofprotein,0.25g/kgofIAAand0.055g/kgof
leucine. Since the study of Witard et al limited the amount of
exercised muscles to the lower limbs, Macnaughton et al
55
compared the MPS response to the ingestion of 20 vs 40 g of
the same whey product after performing a whole-body resis-
tance exercise routine including upper and lower muscle
groups. In addition, the inuence of the participantsbody
size was also analyzed. Results demonstrated that although
both doses, 20 and 40 g signicantly increased MPS, the
highest dose elicited a signicant superior (+20%) MPS
response during 5 hrs after the completion of the workout.
Furthermore, no difference in the post-exercise MPS response
to protein ingestion between participants with a relatively small
or large amount of fat-free mass (~59 vs 77 kg, respectively)
was observed. When the relative intake is considered, for the
20 g dose, 0.200.26 g/kg of protein, 0.100.13 g/kg of IAA
and 0.0220.028 g of leucine was administered. Consequently,
twice these amounts (0.400.52 g/kg of protein, 0.200.26 g/
kg of IAA and 0.0440.056 g of leucine) were ingested for the
40 g intake. It seems that the training volume and the amount of
muscle exercised during the workout, rather than the body size
possessed by the individual, impact on the determination of the
effective optimal protein dose to maximally stimulate MPS
during the post-training period.
In summary, the current evidence suggests that in young
individuals, there is a minimum threshold amount of both IAA
(~0.10 g/kg) and leucine (~0.010 g/kg) needed to stimulate
MPS at rest and during the post-exercise recovery time.
However, higher doses (~0.20 and >0.040 g/kg of IAA and
leucine, respectively) are needed to optimally stimulate MPS
after very demanding exercise sessions (Figure 2). Even
though the requested amount of IAA could be satised with
different protein sources, whey protein extract seems to be
more efcient on a gram per gram basis.
Studies analyzing the long-term
effect of combining whey protein
with resistance exercise to
maximize muscle mass gain
Previous
4
and more recent meta-analysis
6
supports the
notion that as the training level increases, the more rele-
vant is the role of protein supplementation in maximizing
the anabolic response to resistance training. Although a
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minimum daily protein intake of 1.6 or as high as 2.2 g/kg
appears to be the most inuential factor in trained indivi-
duals focused on optimizing muscle mass accretion,
39
and
only a small to modest, non-statistical signicant,
improvement can be obtained by any additional protein
supplementation,
6,39
from a practical point of view, a
potentially slightly superior result obtained by a higher
protein ingestion will still be important for trained
individuals.
2
For instance, the meta-analysis of Naclerio
and Larumbe-Zabala
2
reported that in well-trained ath-
letes, an extra-increment of 24% in fat-free mass can be
obtained from combining the ingestion of whey protein
products with regular resistance training. Although these
gures can be considered modest and are likely not to be
statistically signicant, for a typical trained 80 kg athlete
an extra-gain of ~1.6 to 3.2 kg represents a valuable out-
come, particularly if produced after relatively short inter-
vention periods (612 weeks).
The recent meta-analysis from Morton et al
6
suggests
that protein supplementation augmented gains in muscle
mass, with daily protein intakes of 1.6 g/kg body mass,
being a plausible upper limit for eliciting lean mass accre-
tion. Nonetheless, a potential confounding variable is the
lack of an accurate control of the diet ingested by the
participants. For instance, in meta-analysis of Naclerio
and Larumbe-Zabala
2
that included randomized controlled
trials for young resistance-trained individuals, almost all the
studies monitored the diet using 34 days diet records. Only
the study of Joy et al
28
provided specic diet instructions in
terms of macronutrient distribution rate, however, the daily
amount of protein per kg of body mass was not reported.
Similarly, in the recent meta-analysis of Morton et al,
6
the
only three studies
5759
that analyzed the impact of whey
protein products on lean mass in young resistance-trained
participants, also monitored their diet using a 34-day daily
record. Although this approach has been extensively used, it
is worth saying that it does not provide an ideal scenario to
standardize and provide accurate information pertaining to
participantsindividual dietary intake.
60
As the amount of
protein consumed from the supplement constituted only a
fraction of the total dietary protein ingested during inter-
ventions, giving a pre-packed diet to participants during the
study would offer a more accurate estimation of the impact
of whey on the observed training outcomes when a subop-
timal (eg, <1.6 kg/kg/d) or an optimal (>1.6 to 2 g/kg/d) diet
protein intake is provided. For instance, two studies using
trained individuals reported dissimilar outcomes regarding
the impact of whey protein supplementation on muscle
mass accretion in resistance-trained athletes. Cribb et al
(2006) observed higher lean mass improvements in recrea-
tional bodybuilders who were ingesting >1.6 g/kg of protein
(estimated by a 3-day diet record analysis) and further
0.10 0.20 0.30
~0.10 kg of Leucine
~0.060 g/kg of IAA
>0.10 g/kg
~0.10 kg of Leucine
~0.060 g/kg of IAA
>0.10 g/kg of protein
>0.40 g/kg of protein
Exercise conditions
B
AMinimal effective doses
Optimal effective doses
Resting conditions
Estimated MPS response
Estimated MPS response
>0.20 g/kg of IAA
>0.040 g/kg of Leucine
~0.24 g/kg of protein
>0.10 g/kg of IAA
>0.010 g/kg of Leucine
0.40 0.50
Grams of protein per kg body mass per serving
0.10 0.20 0.30 0.40 0.50
Grams of protein per kg body mass per serving
Figure 2 Theoretical model, showing the effect of a minimal and an optimal single dose (g/kg of body mass) of high-quality protein, IAA and leucine for stimulating muscle
protein synthesis at rest (A) and after training (B).
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supplemented their diet with the addition of 1.5 g/kg/d of
WPH isolate vs the same amount of casein over a 10-week
intervention period.
61
Conversely, a more recent study
56
reported similar gains in lean mass over a 6-week resistance
training intervention combined with the ingestion of 1) 25 g
of whey 2) incremental whey protein ingestion protocol
from 25 to 150 g/d from weeks 1 to 6; or (iii) 30 g of
maltodextrin. All participants, regardless of the group, con-
sumed >2.0 g/kg/d of dietary protein. Authors concluded
that the ingestion of low (25 g/d) or high (25150 g/d) whey
protein daily doses may not provide substantial benets in
promoting hypertrophy when protein intake is >1.6 g/kg/d.
Even though Haun et al
56
intended to control the diet based
on participantsenergy expenditure, the participants were
instructed to self-report their dietary intake but some of
them were unable to meet this requirement. Additionally,
although, participants were instructed to refrain from ergo-
genic aids throughout the duration of the study, if consumed
prior to the study, there were not restricted from using
creatine monohydrate which has a signicant impact on
muscle mass accretion.
62
In summary, in resistance-trained individuals, integrat-
ing whey protein into their habitual diet represents a valid
nutritional strategy for maximizing muscle mass gain as a
result of middle (~6 weeks) to long duration (>12 weeks)
resistance training intervention. These maximizing effects
are minimized when the total daily protein intake achieves
a minimum of 1.6 g/kg. Nonetheless, the current litera-
ture is still unable to accurately analyze the contribution of
the supplement to the daily protein intake. This further
confounds the measured outcomes and is potentially a
source of variation between the observed effects. In this
context it would be appropriate to analyze the convenience
of using whey protein as a high-quality protein-rich food
that can be integrated into the diet to help athletes to
achieve the required daily amount of protein, thereby
facilitating the ingestion of protein under special circum-
stances where the access to more traditional forms of foods
(steak, chicken, eggs) becomes more difcult, eg, before,
during or after training.
Co-ingestion with other
macronutrients
Different multi-ingredient admixtures combining whey
protein with carbohydrates,
63,64
other protein sources
such as casein,
57
bovine colostrum,
65
beef,
66
AAs,
57,67
creatine monohydrate,
44
β-hydroxy-βmethylbutyrate
(HMB)
68
or L-carnitine
69,70
have been proposed for max-
imizing resistance training outcomes in athletes.
Combining carbohydrates and whey protein has shown to
enhance cellular hydration, glycogen resynthesis and favor
positive protein balances,
71
compared to the ingestion of
whey protein or AAs on their own. These benecial effects
are in part related to higher insulin anabolic-related stimuli
caused by the addition of carbohydrates to whey protein.
49,72
Since insulin initiates a suppression of muscle protein break-
down via the ubiquitous proteasome pathway,
73
the co-inges-
tion of carbohydrate acts as an optimizing, permissive
nutrient for achieving a more favorable net muscle protein
balance. Indeed, in the absence of sufcient blood AA avail-
ability, the carbohydrate-induced insulin concentration rise
will likely target a suppression of muscle protein breakdown
with no additional stimulation of MPS.
74
Multi-ingredients admixtures combining whey, with car-
bohydrates, casein, AAs and creatine monohydrate have
shown superior enhancement effects on gaining lean mass
compared to the ingestion of whey protein or carbohydrates
alone.
2
Kerksick et al
57
reported signicant increases in fat-
free mass in 36 resistance-trained men after combining a 10-
week strength training program with the ingestion of 40 g
whey, plus 8 g casein and 2 g of carbohydrates, compared
with both a carbohydrate-placebo and a similar multi-ingre-
dient containing only 40 g of whey enriched with 3 g of
BCAAs, 5 of glutamine and 2 g of carbohydrates. Authors
concluded that the co-ingestion of whey and casein may be
more effective to maximize muscle accretion compared to
the ingestion of only one protein source.
Cribb et al
75
compared the effects of ingesting four dif-
ferent supplements: 1) whey protein only; 2) whey plus
creatine monohydrate; 3) creatine plus carbohydrate and 4)
carbohydrate only, on muscle mass in a group of recreational
male bodybuilders over an 11-week intervention period.
Supplementation with whey protein only, whey protein plus
creatine monohydrate, and carbohydrates plus creatine
monohydrate, resulted in greater hypertrophy responses
compared with the ingestion of carbohydrates alone.
Additionally, the consumption of creatine monohydrate
mixed with whey protein or carbohydrate resulted in similar
improvements that were still signicantly greater compared
with the ingestion of only carbohydrates or whey. More
recently, Jakubowski et al
68
observed no differences between
ingesting two daily 25 g doses of whey protein enriched with
1.5 g of HMB, or 1.5 of leucine during a 12-week periodized
resistance training program on increasing muscle mass in
trained men. On average, for all the participants regardless
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of the group, 25 g of whey provided ~0.29 g/kg of protein
0.14 g/kg of IAA and >0.025 g/kg of leucine per intake.
Moreover, all participants ingested an average of 1.81.9 g/
kg/d of protein from the diet. It is possible that for individuals
consuming a daily protein intake of ~1.6 g/kg, when the
amount of IAA and leucine per intake reaches a threshold
(~0.10 and 0.010 g/kg, respectively), no further stimulus on
the MPS response will be produced by the addition of leucine
and its metabolite HMB.
7
Taken together, the available evidence supports the
benets of adding carbohydrates, creatine monohydrate
or other protein sources to whey for maximizing muscle
mass gain in resistance-trained individuals. Nonetheless,
the additional benets of adding AA or derivatives (eg,
HMB) remain unclear and will be limited by the total daily
protein intake and the relative amount (g/kg of body mass)
of IAA and leucine ingested in each singular intake.
Conclusions
A good quality protein source for adults has been dened
as one that meets at least 100% of all IAA requirements if
0.66 g/kg/day of this protein source is ingested.
To reach the minimum daily nutritional requirement of
leucine (0.039 g/kg), the ingested protein sources should
provide an average of 0.059 mg/g of digestible leucine.
In certain circumstances, such as regular exercise
training, whey protein sources (eg, WPI, WPC) pos-
sessing higher (>1) leucine AARR may be more
appropriate to satisfy the physiological demands of
exercise, favoring training adaption and outcomes.
The currently available evidence supports the use of
whey protein to optimize muscle mass gain in resis-
tance training individuals.
At rest, young individuals may require a minimum thresh-
old amount of >010/kg of protein, providing ~0.060 g/kg
of IAA and ~0.010 g/kg of leucine per serving to stimu-
late MPS. Higher doses of ~0.24 g/kg of protein per
intake, including >0.10 g/kg of IAA and >0.010 g/kg of
leucine may be needed to maximize MPS response.
Under exercise conditions, higher singular doses of
protein may help to optimally stimulate MPS
response. For instance, after very demanding exercise
sessions (involving higher workout volumes and a
large amount of exercising muscle mass) the inges-
tion of >0.40 g/kg of high-quality protein providing
~0.20 g/kg of IAA and >0.040 g/kg or leucine could
be considered. In this context, compared to other
protein sources (pea, rice, soy or beef), the use of
whey protein extracts (WPI, WPC or WPH) seems to
be more efcient, on a gram per gram basis.
In resistance-trained individuals the integration of
different form of whey protein products in the diet
may be considered as a valid nutritional strategy to
satisfy the physiological demands and maximize
training adaptation, eg, gaining muscle mass.
These enhancement effects are minimized when
the total daily protein intake achieves a minimum
of 1.6 g/kg.
Extra benecial effects of whey protein-containing
supplement on lean mass accretion are most evident
when consumed as part of a multi-ingredient, con-
taining carbohydrates, creatine monohydrate and
other protein sources such as casein.
Practical application and futures
perspectives
The integration of protein supplements as a part of regular diet
represents a valid procedure to satisfy nutritional demands and
avoid limitations in performance outcomes caused by a sub-
optimal nutritional supply within the athletic context.
Whey protein extracts can be used to optimize
exercise-induced benets. Compared with the habitual
protein-rich foods (eggs, cheeses, meat, milk, etc.),
whey protein supplements possess a higher digestibil-
ity, leading to a rapid rise in the postprandial aminoa-
cidemia. Even though muscles remain sensitized to
protein ingestion for at least 24 hrs following
exercises,
76
from a practical viewpoint some athletes
may struggle, particularly those with high body masses,
to consume enough protein to meet their required daily
needs (>1.6 g/kg). Therefore, the pragmatic recommen-
dation is for an athlete to eat as soon as possible after a
workout, ingesting >0.24 to ~0.4 g/kg of high-quality
protein sources, eg, WPI, WPC or WPH. In this
respect, not eating does not offer any benetregarding
exercise adaptation and may also interfere with the
subsequent training sessions.
44
Based on the current reviewed literature, the following
considerations are proposed for futures studies or interven-
tion protocols.
The optimal dose of protein to be ingested in the
post-workout meal needs to be determined based on
each specic workout conguration.
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Whole-body resistance exercise routines involving larger
muscle mass may require higher protein doses to max-
imize the anabolic effects during the post-exercise time.
Studies using higher volumes along with high-intensity
training sessions, typically designed for increasing perfor-
mance or gaining muscle mass in athletes from different
disciplines (American football, rugby, bodybuilding,
wrestling, judo, etc.) characterized by a high component
of strength, may need special attention in determining the
optimal composition of the post-workout meal.
The use of whey protein products should not be
analyzed as an isolated strategy for increasing muscle
mass or enhance performance in athletes. From a
practical perspective, it should be considered as a
valid dietary option to optimize nutrition and facil-
itate exercise-induced adaptions and outcomes.
Future studies should consider the proportional con-
tribution of whey protein products to the total daily
protein intake and reveal its contribution to each
individual meal with particular attention to the pre,
during and post-workout food ingestion.
Disclosure
Fernando Naclerio and Marcos Seijo declare that they
have no conicts of interest relevant to the content of
this review.
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... Raw whey proteins found in milk are highly prized owing to their nutritional value, fast absorption, and high levels of antioxidants, amino acids, and peptides [35]. Whey protein (WP) preparations can be divided into three categories: protein isolates, concentrates, and hydrolysates [36,37]. Whey protein isolates and concentrates are highly adopted in the sports industry, where they help to enhance whole-body protein metabolism and skeletal muscle growth [36,38]. ...
... Whey protein (WP) preparations can be divided into three categories: protein isolates, concentrates, and hydrolysates [36,37]. Whey protein isolates and concentrates are highly adopted in the sports industry, where they help to enhance whole-body protein metabolism and skeletal muscle growth [36,38]. Whey proteins have been shown to increase satiety and suppress the feeling of hunger, thereby reducing short-term food intake [39,40]. ...
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There is growing concern regarding the nutritional value of processed food products. Although thermal pasteurization, used in food processing, is a safe method and is widely applied in the food industry, food products lack quality and nutritional value because of the high temperatures used during pasteurization. In this study, the effect of pulsed electric field (PEF) processing on whey protein content and bacterial viability in raw milk was evaluated by changing the PEF strength and number of pulses. For comparison, traditional pasteurization techniques, such as low-temperature long-time (LTLT), ultra-high temperature (UHT), and microfiltration (MF), were also tested for total whey protein content, bacterial activity, and coliforms. We found that, after treatment with PEF, a significant decrease in total bacterial viability of 2.43 log and coliforms of 0.9 log was achieved, although undenatured whey protein content was not affected at 4.98 mg/mL. While traditional pasteurization techniques showed total bacterial inactivation, they were detrimental for whey protein content: β-lactoglobulin was not detected using HPLC in samples treated with UHT. LTLT treatment led to a significant decrease of 75% in β-lactoglobulin concentration; β-lactoglobulin content in milk samples treated with MF was the lowest compared to LTLT and UHT pasteurization, and ~10% and 27% reduction was observed.
... Leucine plays an essential role in maximizing muscle protein synthesis and attenuating muscle protein breakdown at rest and following exercise (34). The current recommendation for leucine supplementation is a minimum intake of 55 mg•kg -1 •d -1 in healthy young adults (3). ...
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This study explored the effect of Eri silkworm supplementation on body composition, cardiac autonomic function, and lung function in university athletes. This study was a randomized crossover trial. Eighteen male athletes were randomly assigned into either the Eri silkworm Group or the Control Group. Subjects in the Eri silkworm Group were supplemented with 0.20-g protein•kg-1 •BM-1 Eri silkworm in the form of conflakes daily for 4 wks, while subjects in the Control Group were requested to maintain their usual daily activities for 4 wks. Body composition, cardiac autonomic function, and lung function were analyzed prior to and post two study periods. Significantly greater body mass, body mass index, fat-free mass, water mass, protein mass, and mineral mass (all P<0.05) were observed in the Eri silkworm Group when compared to the Control Group after supplementation. Cardiac autonomic function and lung function were not significantly different between the Groups subsequent to supplementation. Eri silkworm supplementation may improve body composition but not cardiac autonomic function and lung function in male university athletes.
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We examined hypertrophic outcomes of weekly graded whey protein dosing (GWP) vs. whey protein (WP) or maltodextrin (MALTO) dosed once daily during 6 weeks of high-volume resistance training (RT). College-aged resistance-trained males (training age = 5 ± 3 years; mean ± SD) performed 6 weeks of RT wherein frequency was 3 d/week and each session involved 2 upper- and 2 lower-body exercises (10 repetitions/set). Volume increased from 10 sets/exercise (week 1) to 32 sets/exercise (week 6), which is the highest volume investigated in this timeframe. Participants were assigned to WP (25 g/d; n = 10), MALTO (30 g/d; n = 10), or GWP (25–150 g/d from weeks 1–6; n = 11), and supplementation occurred throughout training. Dual-energy x-ray absorptiometry (DXA), vastus lateralis (VL), and biceps brachii ultrasounds for muscle thicknesses, and bioelectrical impedance spectroscopy (BIS) were performed prior to training (PRE) and after weeks 3 (MID) and 6 (POST). VL biopsies were also collected for immunohistochemical staining. The GWP group experienced the greatest PRE to POST reduction in DXA fat mass (FM) (−1.00 kg, p < 0.05), and a robust increase in DXA fat- and bone-free mass [termed lean body mass (LBM) throughout] (+2.93 kg, p < 0.05). However, the MALTO group also experienced a PRE to POST increase in DXA LBM (+2.35 kg, p < 0.05), and the GWP and MALTO groups experienced similar PRE to POST increases in type II muscle fiber cross-sectional area (~+300 μm2). When examining the effects of training on LBM increases (ΔLBM) in all participants combined, PRE to MID (+1.34 kg, p < 0.001) and MID to POST (+0.85 kg, p < 0.001) increases were observed. However, when adjusting ΔLBM for extracellular water (ECW) changes, intending to remove the confounder of edema, a significant increase was observed from PRE to MID (+1.18 kg, p < 0.001) but not MID to POST (+0.25 kg; p = 0.131). Based upon DXA data, GWP supplementation may be a viable strategy to improve body composition during high-volume RT. However, large LBM increases observed in the MALTO group preclude us from suggesting that GWP supplementation is clearly superior in facilitating skeletal muscle hypertrophy. With regard to the implemented RT program, ECW-corrected ΔLBM gains were largely dampened, but still positive, in resistance-trained participants when RT exceeded ~20 sets/exercise/wk.
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There exists a large body of scientific evidence to support protein intakes in excess of the recommended dietary allowance (RDA) (0.8g protein/kg/d) to promote the retention of skeletal muscle and loss of adipose tissue during dietary energy restriction. Diet-induced weight loss with as low as possible ratio of skeletal muscle to fat mass loss is a situation we refer to as high quality weight loss. We propose that high quality weight loss is often of importance to elite athletes in order to maintain their muscle (engine) and shed unwanted fat mass, potentially improving athletic performance. Current recommendations for protein intakes during weight loss in athletes are set at 1.6-2.4g protein/kg/d. However, the severity of the caloric deficit and type and intensity of training performed by the athlete will influence at what end of this range athletes choose to be at. Other considerations regarding protein intake that may help elite athletes achieve weight loss goals include the quality of protein consumed, and the timing and distribution of protein intake throughout the day. This review highlights the scientific evidence used to support protein recommendations for high quality weight loss and preservation of performance in athletes. Additionally, the current knowledge surrounding the use of protein supplements, branched chain amino acids (BCAA), β-Hydroxy β-Methylbutyrate (HMB), and other dietary supplements with weight loss claims will be discussed.
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Background Protein intake is essential to maximally stimulate muscle protein synthesis, and the amino acid leucine seems to possess a superior effect on muscle protein synthesis compared to other amino acids. Native whey has higher leucine content and thus a potentially greater anabolic effect on muscle than regular whey (WPC-80). This study compared the acute anabolic effects of ingesting 2 × 20 g of native whey protein, WPC-80 or milk protein after a resistance exercise session. MethodsA total of 24 young resistance trained men and women took part in this double blind, randomized, partial crossover, controlled study. Participants received either WPC-80 and native whey (n = 10), in a crossover design, or milk (n = 12). Supplements were ingested immediately (20 g) and two hours after (20 g) a bout of heavy-load lower body resistance exercise. Blood samples and muscle biopsies were collected to measure plasma concentrations of amino acids by gas-chromatography mass spectrometry, muscle phosphorylation of p70S6K, 4E–BP1 and eEF-2 by immunoblotting, and mixed muscle protein synthesis by use of [2H5]phenylalanine-infusion, gas-chromatography mass spectrometry and isotope-ratio mass spectrometry. Being the main comparison, differences between native whey and WPC-80 were analysed by a one-way ANOVA and comparisons between the whey supplements and milk were analysed by a two-way ANOVA. ResultsNative whey increased blood leucine concentrations more than WPC-80 and milk (P < 0.05). Native whey ingestion induced a greater phosphorylation of p70S6K than milk 180 min after exercise (P = 0.03). Muscle protein synthesis rates increased 1–3 h hours after exercise with WPC-80 (0.119%), and 1–5 h after exercise with native whey (0.112%). Muscle protein synthesis rates were higher 1–5 h after exercise with native whey than with milk (0.112% vs. 0.064, P = 0.023). Conclusions Despite higher-magnitude increases in blood leucine concentrations with native whey, it was not superior to WPC-80 concerning effect on muscle protein synthesis and phosphorylation of p70S6K during a 5-h post-exercise period. Native whey increased phosphorylation of p70S6K and muscle protein synthesis rates to a greater extent than milk during the 5-h post exercise period. Trial registrationThis study was retrospectively registered at clinicaltrials.gov as NCT02968888.
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Position statement: The International Society of Sports Nutrition (ISSN) provides an objective and critical review regarding the timing of macronutrients in reference to healthy, exercising adults and in particular highly trained individuals on exercise performance and body composition. The following points summarize the position of the ISSN: 1. Nutrient timing incorporates the use of methodical planning and eating of whole foods, fortified foods and dietary supplements. The timing of energy intake and the ratio of certain ingested macronutrients may enhance recovery and tissue repair, augment muscle protein synthesis (MPS), and improve mood states following high-volume or intense exercise.
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The impact of animal protein blend supplements in endurance athletes is scarcely researched. The authors investigated the effect of ingesting an admixture providing orange juice and protein (PRO) from beef and whey versus carbohydrate alone on body composition and performance over a 10-week training period in male endurance athletes. Participants were randomly assigned to a protein (CHO + PRO, n = 15) or a nonprotein isoenergetic carbohydrate (CHO, n = 15) group. Twenty grams of supplement mixed with orange juice was ingested postworkout or before breakfast on nontraining days. Measurements were performed pre- and postintervention on body composition (by dual-energy X-ray absorptiometry), peak oxygen consumption (V˙O2peak), and maximal aerobic speed. Twenty-five participants (CHO + PRO, n = 12; CHO, n = 13) completed the study. Only the CHO + PRO group significantly (p < .05) reduced whole-body fat (mean ± SD) (-1.02 ± 0.6 kg), total trunk fat (-0.81 ± 0.9 kg), and increased total lower body lean mass (+0.52 ± 0.7 kg), showing close to statistically significant increases of whole-body lean mass (+0.57 ± 0.8 kg, p = .055). Both groups reduced (p < .05) visceral fat (CHO + PRO, -0.03 ± 0.1 kg; CHO, -0.03 ± 0.5 kg) and improved the speed at maximal aerobic speed (CHO + PRO, +0.56 ± 0.5 km/hr; CHO, +0.35 ± 0.5 km/hr). Although consuming animal protein blend mixed with orange juice over 10 weeks helped to reduce fat mass and to increase lean mass, no additional performance benefits in endurance runners were observed.
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Background: Older women may not be consuming enough protein to maintain muscle mass. Augmentation of protein intake with leucine may enhance the muscle protein synthetic response in older women to aid in maintaining muscle mass. Objective: We measured the acute (hourly) and integrated (daily) myofibrillar protein synthesis (myoPS) response to consumption of a high-quality mixed protein beverage compared with an isonitrogenous protein beverage with added leucine. Design: In a parallel design, free-living, healthy older women (aged 65-75 y, n = 11/group) consumed a fixed, weight-maintaining diet with protein at 1.0 g · kg-1 · d-1 and were randomly assigned to twice-daily consumption of either 15 g milk protein beverage containing 4.2 g leucine (LEU) or 15 g mixed protein (milk and soy) beverage containing 1.3 g leucine (CON). Unilateral leg resistance exercise allowed a determination of acute ([13C6]-phenylalanine infusion, hourly rate) and integrated (deuterated water ingestion, daily rate) exercised and rested myoPS responses. Results: Acute myoPS increased in response to feeding in the rested (CON: 13% ± 4%; LEU: 53% ± 5%) and exercised (CON: 30% ± 4%; LEU: 87% ± 7%) leg in both groups, but the increase was greater in LEU (P < 0.001). Integrated myoPS increased during the supplementation period in both legs (rested: 9% ±1%; exercised: 17% ± 2%; P < 0.001) in LEU, but in the exercised leg only (7% ± 2%; P < 0.001) in CON. Conclusions: A 15-g protein-containing beverage with ∼4 g leucine induced greater increases in acute and integrated myoPS than did an isonitrogenous, isoenergetic mixed-protein beverage. Declines in muscle mass in older women may be attenuated with habitual twice-daily consumption of a protein beverage providing 15 g protein and higher (4.2 g/serving) amounts of leucine. This trial was registered at clinicaltrials.gov as NCT02282566.
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Consumption of sufficient dietary protein is fundamental to muscle mass maintenance and overall health. Conventional animal-based protein sources such as meat (ie, beef, pork, lamb), poultry, fish, eggs, and dairy are generally considered high-quality sources of dietary protein because they meet all of the indispensable amino-acid requirements for humans and are highly digestible. However, the production of sufficient amounts of conventional animal-based protein to meet future global food demands represents a challenge. Edible insects have recently been proposed as an alternative source of dietary protein that may be produced on a more viable and sustainable commercial scale and, as such, may contribute to ensuring global food security. This review evaluates the protein content, amino-acid composition, and digestibility of edible insects and considers their proposed quality and potential as an alternative protein source for human consumption.