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Dietary protein for athletes: From requirements to optimum adaptation

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Abstract

Opinion on the role of protein in promoting athletic performance is divided along the lines of how much aerobic-based versus resistance-based activity the athlete undertakes. Athletes seeking to gain muscle mass and strength are likely to consume higher amounts of dietary protein than their endurance-trained counterparts. The main belief behind the large quantities of dietary protein consumption in resistance-trained athletes is that it is needed to generate more muscle protein. Athletes may require protein for more than just alleviation of the risk for deficiency, inherent in the dietary guidelines, but also to aid in an elevated level of functioning and possibly adaptation to the exercise stimulus. It does appear, however, that there is a good rationale for recommending to athletes protein intakes that are higher than the RDA. Our consensus opinion is that leucine, and possibly the other branched-chain amino acids, occupy a position of prominence in stimulating muscle protein synthesis; that protein intakes in the range of 1.3-1.8 g · kg(-1) · day(-1) consumed as 3-4 isonitrogenous meals will maximize muscle protein synthesis. These recommendations may also be dependent on training status: experienced athletes would require less, while more protein should be consumed during periods of high frequency/intensity training. Elevated protein consumption, as high as 1.8-2.0 g · kg(-1) · day(-1) depending on the caloric deficit, may be advantageous in preventing lean mass losses during periods of energy restriction to promote fat loss.
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Dietary protein for athletes: From requirements to
optimum adaptation
Stuart M. Phillips a & Luc J.C. Van Loon b
a Department of Kinesiology, Exercise Metabolism Research Group, McMaster University,
Hamilton, Ontario, Canada
b Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and
Metabolism, Maastricht University Medical Centre, Maastricht, Netherlands
Available online: 09 Dec 2011
To cite this article: Stuart M. Phillips & Luc J.C. Van Loon (2011): Dietary protein for athletes: From requirements to
optimum adaptation, Journal of Sports Sciences, 29:sup1, S29-S38
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Dietary protein for athletes: From requirements to optimum adaptation
STUART M. PHILLIPS
1
& LUC J. C. VAN LOON
2
1
Department of Kinesiology, Exercise Metabolism Research Group, McMaster University, Hamilton, Ontario, Canada and
2
Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism,
Maastricht University Medical Centre, Maastricht, Netherlands
(Accepted 29 August 2011)
Abstract
Opinion on the role of protein in promoting athletic performance is divided along the lines of how much aerobic-based
versus resistance-based activity the athlete undertakes. Athletes seeking to gain muscle mass and strength are likely to
consume higher amounts of dietary protein than their endurance-trained counterparts. The main belief behind the large
quantities of dietary protein consumption in resistance-trained athletes is that it is needed to generate more muscle protein.
Athletes may require protein for more than just alleviation of the risk for deficiency, inherent in the dietary guidelines, but
also to aid in an elevated level of functioning and possibly adaptation to the exercise stimulus. It does appear, however, that
there is a good rationale for recommending to athletes protein intakes that are higher than the RDA. Our consensus opinion
is that leucine, and possibly the other branched-chain amino acids, occupy a position of prominence in stimulating muscle
protein synthesis; that protein intakes in the range of 1.3–1.8 g kg
71
day
71
consumed as 3–4 isonitrogenous meals will
maximize muscle protein synthesis. These recommendations may also be dependent on training status: experienced athletes
would require less, while more protein should be consumed during periods of high frequency/intensity training. Elevated
protein consumption, as high as 1.8–2.0 g kg
71
day
71
depending on the caloric deficit, may be advantageous in
preventing lean mass losses during periods of energy restriction to promote fat loss.
Keywords: Leucine, hypertrophy, protein turnover
Introduction
While the net rates of protein synthesis and
degradation, collectively referred to as ‘‘turnover’’,
are relatively high in humans, the net loss (synthesis
minus breakdown) of amino acids is relatively low.
For example, whole body protein breakdown might
be 280 g day
71
in a 70 kg male with 28–32 kg of
skeletal muscle tissue. Whole body protein synthesis
would be about 280 g day
71
also; however, there
are transient periods in which protein breakdown
exceeds synthesis and in that time there is a net loss
of amino acids necessitating the consumption of
protein to replace losses. Those losses are typically
about 40–60 g day
71
for a sedentary person
weighing 70–90 kg and it is debatable what the
losses would be in athletes, be they aerobically
trained or resistance trained. The current US and
Canadian RDA and Australian RDI tell us that a
daily protein intake somewhere between 0.75 and
0.80 g kg
71
will meet the needs of about 98% of
the population. The most recent American College
of Sports Medicine position stand (Gerovasili et al.,
2009) on dietary practices for athletes recommends
a protein intake of 1.2–1.7 g kg
71
day
71
for
endurance- and resistance-trained athletes. All of
the above recommendations are based on data from
studies of nitrogen balance. From a physiological
perspective, to be in nitrogen – or protein – balance
means only that protein (nitrogen) intake is balanced
by protein (nitrogen) loss. It is hard to imagine what
variable an athlete or their coach might believe is
associated with being in nitrogen balance, least of all
performance. It is also well acknowledged that the
nitrogen balance technique has serious technical
drawbacks, which may result in requirements that are
too low. The reader is referred to the most recent
WHO/FAO/UNU technical report (Sakuma et al.,
2009) for a detailed and in-depth discussion of the
various drawbacks of the nitrogen balance approach.
Despite the technical problems of nitrogen bal-
ance, a number of studies have attempted to define
what protein intakes would be required to achieve
Correspondence: S. M. Phillips, Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ONT L8S 4K1, Canada.
E-mail: phillis@mcmaster.ca
Journal of Sports Sciences, 2011; 29(S1): S29–S38
ISSN 0264-0414 print/ISSN 1466-447X online Ó2011 Taylor & Francis
http://dx.doi.org/10.1080/02640414.2011.619204
Downloaded by [McMaster University] at 09:16 09 December 2011
a state of nitrogen balance, and thus define an
athletic protein requirement, in athletes (Friedman &
Lemon, 1989; Lemon, Tarnopolsky, MacDougall, &
Atkinson, 1992; Tarnopolsky, MacDougall, &
Atkinson, 1988). Data from these studies leads to
the conclusion that the protein needs of athletes
can be as high as twice the RDA/RDI (Friedman &
Lemon, 1989; Lemon et al., 1992; Tarnopolsky
et al., 1988). At the same time, a number of
longitudinal studies have reached the conclusion
that exercise training in novices actually reduces
protein utilization and requirements due to reduced
activation of amino acid oxidation/catabolism in
endurance athletes (McKenzie et al., 2000), or that
resistance exercise induces a more efficient use of
amino acids arising from muscle protein breakdown
(Hartman, Moore, & Phillips, 2006; Moore et al.,
2007). What is more important perhaps than
debating what nitrogen balance means for an athlete
is to look at protein from a functional perspective and
to try and recognize that an ‘‘optimal’’ intake for
athletes might exist that is not predicated on merely
satisfying a minimal requirement and thus being in
nitrogen balance. It is also recognized that such an
intake is not easy to define. The function that athletes
care most about is optimal performance in their sport
of choice. Often improvements in performance will
involve gaining muscle mass and potentially also
losing fat mass, as a high lean-to-fat body weight
ratio is desirable in several sports. With this frame-
work in mind, we can look at specific situations
where protein can act as a substrate for the synthesis
of new muscle proteins, leading eventually to net
muscle accretion or to the repair of excessive protein
damage, and at strategies to aid in fat mass loss while
still maintaining lean mass. Thus, the goal of this
review is to provide some guidance as to what an
athletic ‘‘optimal’’ protein intake might be.
The role of protein in training-induced
adaptation
Muscle mass is normally fairly constant during adult
life up to the fourth or fifth decade, when the slow
process of sarcopenia is thought to begin (Evans,
1995). The maintenance of muscle mass is a balance
between muscle protein synthesis (MPS) and muscle
protein breakdown (MPB). The algebraic difference
between MPS and MPB, to yield net muscle protein
balance (NPB), is the operative variable determining
gain or loss of muscle mass (Burd, Tang, Moore, &
Phillips, 2009). Obviously, from the standpoint of
obtaining an optimum adaptation, athletes look to
maximize the adaptive responses to their training
bouts by maximizing their NPB. This is accom-
plished through the synergistic action of both
exercise and amino acid/protein ingestion to promote
increases in MPS (Moore, Phillips, Babraj, Smith, &
Rennie, 2005; Moore et al., 2009b). The key
processes underlying these adaptations, involving
gene transcription, protein signalling, and translation
initiation, are too complex and tangential to the main
focus of this review; however, the reader is referred to
several reviews on these topics for more in-depth
discussion of these mechanisms (Hundal & Taylor,
2009; Mahoney & Tarnopolsky, 2005; Rennie,
Wackerhage, Spangenburg, & Booth, 2004; Sarbas-
sov et al., 2004).
Protein ingestion following exercise reduces in-
dices of damage such as release of creatine kinase
(Greer, Woodard, White, Arguello, & Haymes,
2007; Rowlands, Thorp, Rossler, Graham, &
Rockell, 2007; Rowlands et al., 2008; Valentine,
Saunders, Todd, & St. Laurent, 2008). How dietary
protein ingestion might affect muscle damage is
unknown. There is some indication that post-
exercise protein feeding might support an enhanced
performance (Cockburn, Stevenson, Hayes, Robson-
Ansley, & Howatson, 2010; Rowlands et al., 2008;
Saunders, Moore, Kies, Luden, & Pratt, 2009), but
no plausible mechanism for this effect is readily
available and not all data support such a conclusion
(Cermak, Solheim, Gardner, Tarnopolsky, & Gibala,
2009; van Essen & Gibala, 2006). What cannot be
ignored, however, is the fact that protein consump-
tion is necessary for MPS to be stimulated to result
in a positive NPB. Athletes engaged in resistance
exercise would no doubt find benefit in repeated
periods of positive protein balance to eventually
allow for muscle protein accretion and subsequent
hypertrophy to occur. It is less clear what benefit
endurance-trained athletes may derive, but it is not
unreasonable to suggest that mitochondrial protein
synthesis would proceed at a higher rate with
ingestion of protein versus no protein (Wilkinson
et al., 2008). The supposition would then be that
endurance athletes may experience a greater train-
ing-induced increase in mitochondrial volume and
enhanced adaptation in response to training, but
such a thesis has not been tested. A recent paper did
find that immediate post-exercise supplementation
with protein versus carbohydrate did result in greater
improvements in peak oxygen uptake in older men
(Robinson, Turner, Hellerstein, Hamilton, & Miller,
2011); however, how protein accomplished this is
uncertain.
Protein serves both as a substrate and a trigger for
adaptation after both resistance and aerobic exercise.
If protein provision in close temporal proximity to
exercise promotes a better adaptation (i.e. greater
muscle mass gain or greater gains in oxidative
capacity), then this would serve as a basis for a
framework in which we can begin to discuss an
optimum protein intake for athletes. There is
S30 S. M. Phillips & L. J. C. van Loon
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evidence to support this concept in resistance
training studies (Cribb & Hayes, 2006; Hartman
et al., 2007; Holm et al., 2008), but not for aerobic-
based training. However, inherent in the concept
that protein consumption promotes training is the
need to focus on protein intakes that create optimum
adaptation rather than those tied merely to nitrogen
balance. Viewed from this perspective, there are
important messages for athletes in terms of quantity,
timing, and quality of protein intake in relation to the
training stimulus.
What quantity of protein should athletes
consume?
The US Dietary Reference Intakes (DRI) specify a
daily dietary protein intake for all individuals aged 19
years and older of 0.8 g kg
71
(Institute of Medi-
cine, 2005). This recommended dietary allowance
(RDA) is cited as adequate for almost all persons.
This amount of protein would be considered by
many athletes as the amount to be consumed in a
single meal, particularly for strength-trained athletes.
There do exist, however, published data to suggest
that individuals habitually performing resistance
and/or endurance exercise require more protein than
their sedentary counterparts (Friedman & Lemon,
1989; Lemon et al., 1992; Tarnopolsky et al., 1988,
1992). The RDA values for protein are clearly set at
‘‘the level of protein judged to be adequate . . . to
meet the known nutrient needs for practically all
healthy people’’ (Institute of Medicine, 2005). The
RDA covers protein losses with margins for inter-
individual variability and protein quality, but the
notion of consumption of ‘‘extra’’ protein above
these levels to cover increased needs due to physical
activity is not considered.
Studies of protein requirements in athletes have
shown an increased requirement for protein in
strength-trained (Lemon et al., 1992; Tarnopolsky
et al., 1988, 1992) and endurance-trained athletes
(Friedman & Lemon, 1989; Meredith, Zackin,
Frontera, & Evans, 1989; Tarnopolsky et al.,
1988). Increased protein requirements for indivi-
duals engaging in resistive activities might be
expected due to the need for ‘‘extra’’ dietary protein
to synthesize new muscle or repair muscle damage.
On the other hand, endurance exercise is associated
with marked increases in leucine oxidation (McKen-
zie et al., 2000; Phillips, Atkinson, Tarnopolsky, &
MacDougall, 1993), which would elevate overall
requirements for protein (if other amino acids are
also oxidized to an appreciable extent), or at least for
leucine. The shortcomings of nitrogen balance have
long been recognized, as the adequate protein intake
is calculated from implausibly high retentions of
nitrogen at high protein intakes (Hegsted, 1976;
Young, 1986; Young, Gucalp, Rand, Matthews, &
Bier, 1987). This highlights the need for another
approach to examining protein requirements; tracer-
derived estimations of protein requirements are one
alternative method. Using this approach, it was
reported that consumption of a ‘‘low’’ protein diet
(0.86 g kg
71
day
71
) by a group of strength-
trained athletes resulted in an accommodated state
in which whole body protein synthesis was reduced
compared with medium (1.4 g kg
71
day
71
) and
high (2.4 g kg
71
day
71
) protein diets (Tarno-
polsky et al., 1992). No difference was seen in whole
body protein synthesis between the medium and high
protein diets, but amino acid oxidation was elevated
on the high protein diet, indicating that this protein
intake was providing amino acids in excess of the
rate at which they could be integrated into body
proteins. It should be emphasized that these results
do not mean that 1.4 g kg
71
day
71
was required
to cover dietary protein needs, but simply that
0.86 g kg
71
day
71
was not sufficient to allow
maximal rates of protein synthesis. It is not known
what body proteins were being made at a sub-
maximal rate at 0.86 g kg
71
day
71
, but if muscle
protein synthesis was adversely affected then clearly
these data would be of relevance to athletes.
A protein dose–response relationship was shown
to exist following resistance exercise (Moore et al.,
2009a). In this study, isolated egg protein was fed to
young men in graded doses from 0 to 40 g after
resistance exercise and MPS was measured. Muscle
protein synthesis showed a graded increase from 0 to
20 g and despite doubling protein intake to 40 g,
there was no difference in MPS. At the same time
that the plateau in MPS was observed, the oxidation
of leucine was significantly elevated over that seen at
rest and following doses of 5 g and 10 g of protein.
The conclusion from these data was that an intake of
protein of *20 g in larger men (85 kg) was sufficient
to maximally stimulate MPS, but that higher intakes
would not offer any further benefit and the excess
amino acids were oxidized (Moore et al., 2009a).
Interestingly, the dose of essential amino acids
(EAA) in 20 g of egg protein (i.e. 8.3 g) that was
found to maximally stimulate MPS was remarkably
similar to that seen at rest, which was 10 g of EAA
(Cuthbertson et al., 2005). These data (Moore et al.,
2009a) suggest that an optimum quantity of protein
to consume to maximally stimulate MPS after
resistance exercise appears to be around 20–25 g of
high-quality protein.
Recent data from Harber and colleagues (2010)
suggest that feeding (a drink at 5 kcal kg
71
, which
delivered for every 5 kcal: 0.83 g carbohydrate,
0.37 g protein, and 0.03 g fat) did not enhance
mixed MPS after a 1 h cycle ride at *72% of peak
oxygen uptake; however, changes in mixed MPS may
Dietary protein for athletes S31
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not capture the feeding-induced enhancement of
mitochondrial protein synthesis. Thus, at this time a
similar conclusion to that reached by Moore and
colleagues on a maximally effective dose of protein
is not available for those engaging in endurance
exercise, but it would be prudent to measure not only
mixed MPS but mitochondrial protein synthesis to
isolate the potential effects of the exercise bout on
that fraction.
Timing of protein consumption
Athletes have the choice of consuming protein
before, during, and after exercise. There are different
theories as to which period promotes an optimum
adaptation, but in the case of resistance exercise
almost all of them relate to the ability of protein to
provide amino acid precursors to either support MPS
or inhibit MPB. Protein consumption with respect to
aerobic exercise focusing on peri-workout/event
nutrition is backed by a theory that amino acids
could support some energy-yielding pathways and/or
attenuate muscle damage and enhance performance.
Post-exercise protein consumption may enhance
adaptation by also restoring glycogen, but it appears
that this is the case only if inadequate carbohydrate
is consumed (Jentjens, van Loon, Mann, Wagen-
makers, & Jeukendrup, 2001) and this phenomenon
will not be discussed here.
With respect to resistance exercise, some studies
have shown that pre-exercise protein consumption
can enhance MPS (Tipton et al., 2001) and others
have shown no effect (Fujita et al., 2009; Tipton
et al., 2006). Thus, at this time pre-exercise feeding
appears unlikely to increase MPS and long-term
gains in muscle mass. A number of training studies
have used a combination of pre-exercise and post-
exercise feeding to enhance gains in muscle mass
(Burk, Timpmann, Medijainen, Vahi, & Oopik,
2009; Cribb & Hayes, 2006), so it is impossible to
tell whether the pre-exercise meal imparted any
benefit, since post-exercise meals are unequivocally
beneficial (see below).
Consumption of protein during exercise may
provide amino acids to ‘‘prime the pump’’. In other
words, the amino acids present in the circulation
during exercise may increase MPS and possibly
suppress MPB to enhance protein balance either
during or after the exercise bout. Only one study has
examined peri-workout protein consumption with
resistance exercise (Beelen et al., 2008). In this
study, the ingestion of protein and carbohydrate did
enhance MPS during the exercise bout and into early
recovery, but this did not extend into the overnight
fasted period.
A number of studies have provided endurance-
trained athletes with protein during a workout to
assess the impact of this macronutrient on metabo-
lism and also on performance. Consumption of
protein during endurance exercise results in an
improved whole body protein balance during and
after the exercise bout (Koopman et al., 2004), but
the effects on MPS and MPB are not known. Some
studies have shown that protein provision during
exercise can enhance performance (Saunders et al.,
2009; Valentine et al., 2008), but others have shown
no performance effect (Cermak et al., 2009; van
Essen & Gibala, 2006). Thus, there seems to be little
reason to recommend the ingestion of protein during
aerobic exercise for performance enhancement and
there is no discernible benefit in terms of MPS or
MPB.
It is axiomatic that provision of protein and/or
amino acids to athletes in the post-exercise period,
particularly after resistance exercise, stimulates MPS
(for reviews, see Burd et al., 2009; Drummond,
Dreyer, Fry, Glynn, & Rasmussen, 2009; Koopman,
Saris, Wagenmakers, & van Loon, 2007b; Phillips,
Tang, & Moore, 2009). As might be expected, the
impact of resistance exercise is quite specific for
synthesis of proteins in the myofibrillar protein
fraction (Moore et al., 2009b). There are also reports
that provision of protein after the performance of
aerobic exercise stimulates MPS (Howarth, Moreau,
Phillips, & Gibala, 2009; Levenhagen et al., 2001),
particularly of the mitochondrial protein fraction
(Wilkinson et al., 2008). While there is some debate
about the ‘‘critical’’ nature of the timing of post-
exercise protein consumption, a simple message may
be that the earlier after exercise an athlete consumes
protein the better. This conclusion may seem to gloss
over a number of important studies showing, or not
showing, the benefit of early post-exercise protein
provision with respect to both stimulation of MPS
and/or hypertrophy, but it emphasizes a principle
that athletes would likely benefit from. That is, the
sooner the recovery process following exercise can
begin the better. So while a crucial ‘‘window of
anabolic opportunity’’ is not, at least currently, well
defined, it would make sense that protein provision
should begin as soon as possible after exercise to
promote recovery and possibly to enhance the rate
of – or absolute level of – adaptation.
Protein source and quality
Protein quality is measured using a variety of indices
but the most commonly accepted and understood
index is the protein digestibility corrected amino acid
score or PDCAAS. Using the PDCAAS, a number
of proteins are classified as ‘‘high quality’’, meaning
they have a PDCAAS score of 1.0 or are very close to
1.0. Unsurprisingly, animal-source proteins such as
milk (and the constituent proteins of milk, casein and
S32 S. M. Phillips & L. J. C. van Loon
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whey), egg, and most meats are high quality. Isolated
soy protein, once the anti-nutritional components
are removed, also has a PDCAAS score of 1.0. Use
of the PDCAAS has been criticized, however, since
scores are artificially truncated at 1.0 despite the fact
that isolated milk proteins, casein, and whey proteins
all have scores of *1.2 (Phillips et al., 2009;
Schaafsma, 2005). An obvious question, therefore,
is whether there are any advantages to habitual
consumption of these proteins in terms of promotion
of recovery (increments in MPS and/or suppression
of MPB or less muscle damage) and adaptation
(greater muscle mass accretion or enhancement of
oxidative capacity). In fact, evidence does exist to
support the former thesis that milk proteins, for
example, result in a greater stimulation of MPS after
resistance exercise than the consumption of equiva-
lent protein and macronutrient energy as isolated soy
protein (Wilkinson et al., 2007). Practised over time,
the habitual consumption of milk versus equivalent
soy protein resulted in greater hypertrophy (Hartman
et al., 2007). In addition, comparisons of the
capacity of isonitrogenous quantities of soy, casein,
and whey protein to stimulate MPS both at rest and
following resistance exercise demonstrated the ad-
vantage of whey protein (Tang, Moore, Kujbida,
Tarnopolsky, & Phillips, 2009). The reasons for the
superiority of milk proteins over an ostensibly
nutritionally equivalent protein such as isolated soy
are not clear, but it appears that the amino acid
leucine, possibly in conjunction with the other
branched-chain amino acids (BCAA), could be
critically important.
Leucine is a BCAA that can activate key signalling
proteins resident in the protein kinase B-mammalian
target of rapamycin (mTOR) pathway responsible for
translation initiation. The effects of leucine have
been shown in vitro (Atherton, Smith, Etheridge,
Rankin, & Rennie, 2010) and in vivo (for reviews, see
Drummond & Rasmussen, 2008; Drummond et al.,
2009; Kimball & Jefferson, 2006a, 2006b). Milk
proteins in particular are rich in leucine and this may
explain part of their efficacy in stimulating MPS and
promoting hypertrophy. Whey protein in particular is
highly enriched in leucine, which appears to translate
into a greater ability of this protein fraction to
stimulate muscle growth, at least compared with soy
(Phillips et al., 2009). However, if leucine content is
such a significant factor in stimulating MPS, this
does not explain the finding that whey protein was
more effective than soy, which were both more
effective than casein in stimulating MPS following
resistance exercise when the leucine contents range
from whey with the highest to soy with the lowest
(Tang et al., 2009). A critically important observa-
tion in this study was the rate of appearance of
leucine in the systemic circulation, which was most
rapid following whey protein consumption, inter-
mediate with soy protein, and very slow with casein
(Tang et al., 2009). Thus, even though casein’s
leucine content is higher than that of soy, the
digestion of casein, which clots in the stomach and
so is slowly digested, slowed the appearance of
leucine and prevented systemic leucine concentra-
tions from increasing to a sufficient level to turn on
MPS. This ‘‘leucine trigger’’ hypothesis for MPS is
supported by other observations (Fouillet, Mariotti,
Gaudichon, Bos, & Tome, 2002; Lacroix et al.,
2006). Interestingly, Koopman and colleagues
(2009) reported that partially hydrolysed casein
protein improved the rate of MPS post-consumption
versus the intact protein. Hydrolysis of casein in
this case would allow a more rapid digestion and
absorption of the protein and thus a more rapid
leucinaemia and a more rapid overall aminoacidae-
mia, leading to enhanced MPS (Koopman et al.,
2009). Thus, a higher leucine content and rapidly
digested proteins may be a prudent choice for
athletes to consume as the spike in blood leucine
appears to be critically important in activating MPS.
Sustaining MPS after the initial leucine-mediated
activation may well be dependent on adequate
provision of the other EAA and in particular the
BCAA, which means that supplements of isolated
leucine would likely be of little benefit over and
above consumption of high-quality proteins, at least
for athletes.
Changes in body composition with nutrition
and exercise
The key variable determining weight loss is the
relative energy deficit created by dietary energy
restriction and/or increased energy expenditure.
For athletes in particular, weight loss is often a
desired goal, but an important question is whether
certain patterns of macronutrient consumption can
bring about a better ‘‘quality’’ of weight loss. In this
sense, the quality of weight loss refers to loss of
weight with the highest possible fat-to-lean ratio. In
most situations, loss of inert mass as fat is the desired
goal of athletes. However, it may be that on occasion
an athlete needs to simply lose weight to make a
particular weight class for example, and in this
scenario it is clear that loss of lean mass would be a
‘‘sacrifice’’ that some athletes may be willing to
make. It is also worth noting that a certain amount of
skeletal muscle could be lost without much, or any,
adverse affect on performance (Degoutte et al., 2006;
Zachwieja et al., 2001), but this appears to depend
on the rate of weight loss (Garthe, Raastad, Refsnes,
Koivisto, & Sundgot-Borgen, 2011). Assuming,
however, that fat mass reduction is what most
athletes would desire during a period of weight loss
Dietary protein for athletes S33
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with the realization that leanness can offer a
competitive advantage, the question is whether there
are optimal ratios of nutrients to consume to achieve
this goal and also avoid nutritional deprivation.
The macronutrient composition of energy-re-
stricted diets and the influence of these ratios on
weight loss is controversial. Many popular weight-
loss diets have set protein at *15% of energy, 530%
lipids, and *50–55% carbohydrates, with reductions
in dietary fat and increases in dietary fibre being
favoured. It is reasonable to reduce energy density
with this ratio of macronutrients and promote weight
loss in the short term, but low satiety and poor
adherence over longer periods are common in people
adhering to a diet with this ratio of macronutrients
(Abete, Astrup, Martinez, Thorsdottir, & Zulet,
2010; Foreyt et al., 2009; Sacks et al., 2009).
Generally speaking, on this diet the tissue composi-
tion of weight loss is 70–80% adipose and 20–30%
lean tissue (almost exclusively skeletal muscle)
(Weinheimer, Sands, & Campbell, 2010). Emerging
evidence suggests that reducing the intake of dietary
carbohydrates is a critically important step in
promoting both greater weight loss and greater loss
of body fat (Abete et al., 2010; Foreyt et al., 2009;
Krieger, Sitren, Daniels, & Langkamp-Henken,
2006). The mechanisms underpinning this effect
are uncertain but may relate to a lower daily blood
glucose concentration and also lower daily insulin
(Feinman & Fine, 2007). Insulin’s primary functions
as a hormone are to promote storage of blood
glucose in skeletal muscle and adipose tissue and to
inhibit lipolysis and promote triglyceride synthesis
and storage rather than release (Feinman & Fine,
2007). Another proven strategy is to reduce not just
the total quantity of carbohydrate but also to globally
lower the glycaemic load of the diet by selecting low
glycaemic-index (GI) carbohydrate sources (for a
review, see Abete et al., 2010). However, following
low carbohydrate, lower GI diets may be a problem
for endurance athletes seeking to compete, since
dietary carbohydrate intakes are recommended to be
higher to allow a more rapid and full recovery of
endogenous glycogen stores (Phillips, 2006). Thus,
at the expense of carbohydrates, a higher protein or
fat intake can obviously compromise performance.
While lower total and relative carbohydrate diets
appear effective, an important question is what
macronutrient should replace the carbohydrate.
Diets moderately high in protein and modestly
restricted in carbohydrate and fat may have more
beneficial effects on body weight homeostasis and
associated metabolic variables (Abete et al., 2010;
Feinman & Fine, 2007; Foreyt et al., 2009; Krieger
et al., 2006; Layman, 2004). This review is aimed at
rather moderate protein diets, but still almost twice
that recommended by the RDA or RDI (20–30%
energy or intakes of 1.8–2.7 g protein kg
71
day
71
, at the expense of carbohydrates), and those
with lower carbohydrates (within 40% energy or
3.6 g carbohydrate kg
71
day
71
).
Increasing dietary protein intake to values higher
than commonly recommended has a beneficial effect
on retention of lean mass during hypoenergetic
periods of weight loss (Abete et al., 2010; Feinman
& Fine, 2007; Foreyt et al., 2009; Krieger et al.,
2006; Layman, 2004). Meta-analyses of trials
(Krieger et al., 2006) have shown that higher protein,
at the expense of carbohydrate, improves the amount
of fat loss and preserves lean tissue. Importantly for
athletes, the weight loss-induced decrement in lean
mass can be offset by performance of resistive
exercise (Layman et al., 2005; MacKenzie, Hamilton,
Murray, Taylor, & Baar, 2009; Mettler, Mitchell, &
Tipton, 2010). Several studies have shown a syner-
gism between resistance exercise and higher protein
content of the diet in terms of enhancing the
retention of lean mass during hypoenergetic periods
(Layman et al., 2005; MacKenzie et al., 2009;
Mettler et al., 2010). Other mechanisms that have
been proposed for why protein is an effective
substitution for dietary carbohydrate have to do with
protein’s satiety-promoting effects, which appear
to be greater than those of carbohydrate and fat.
A comprehensive review of satiety and weight loss is
not possible, however. In addition, the thermogenic
effect of protein consumption has long been known
to be the greatest of all macronutrients.
Other nutrients
The addition of other nutrients to protein may
enhance the metabolic effectiveness of protein in
either stimulating MPS or suppressing MPB. An
important point is that resistance-trained athletes
may be less concerned about restoration of muscle
glycogen as a goal as opposed to endurance-trained
athletes. Nonetheless, an important question, even
for resistance-trained athletes, is whether carbohy-
drate, through insulin, mediates a greater rise in
MPS or suppression of MPB, To date three studies
have addressed this question and none found that the
addition of smaller (20–40 g) or larger (90–120 g)
amounts of carbohydrate resulted in enhanced rates
of MPS or, at least from whole body measures,
suppression of MPB (Glynn et al., 2010; Koopman
et al., 2007a). Even when twice as much carbohy-
drate (50 g as maltodextrin) is added to a sufficient
quantity of protein (25 g of whey) there is no
further stimulation of MPS or suppression of MPB.
Collectively, these findings indicate that so long as
protein intake is sufficient, carbohydrate does little
to augment post-exercise protein turnover (Glynn
et al., 2010; Koopman et al., 2007; Sancak et al.,
S34 S. M. Phillips & L. J. C. van Loon
Downloaded by [McMaster University] at 09:16 09 December 2011
2010). When viewed from a broad perspective,
athletes recovering from exercise would have to serve
four ‘‘masters’’: hydration, restoration of metabolized
carbohydrate, restoration/repair of damaged pro-
teins, and remodelling proteins. Viewed in this light,
protein consumed in a liquid form concurrently with
carbohydrate would provide an optimum ‘‘package’’
of nutrients to achieve these goals. Bovine fluid milk
would likely represent such a package of nutrients
and when consumed as a post-exercise ‘‘recovery’’
drink has been shown to augment lean mass gain
(for a review, see Phillips et al., 2009). As far as
rehydration is concerned, milk has also been shown
to be equivalent or better than water and isotonic
sports drinks in terms of restoring fluid balance
(Shirreffs, Watson, & Maughan, 2007; Watson,
Love, Maughan, & Shirreffs, 2008). A number of
studies have also shown that when consumed after
exercise, flavoured versions of milk (e.g. chocolate),
which most often contain added carbohydrate as a
simple sugar, can enhance subsequent exercise
performance (Karp et al., 2006; Thomas, Morris,
& Stevenson, 2009) and reduce indices of muscle
damage (Gilson et al., 2010). It appears that milk,
and its flavoured varieties, would be an entirely
reasonable and cost-effective alternative to supple-
ments to enhance recovery and enhance performance.
Summary
.Protein consumption can enhance rates of MPS
and possibly lower rates of MPB, thus improv-
ing muscle NPB. The improvement in NPB
appears to accumulate to promote greater
protein retention in the case of resistance
exercise and may enhance training-induced
adaptations with endurance training, although
the latter has yet to be tested.
.A dose of protein that appears to maximally
stimulate MPS appears to be in the range of
20–25 g, although this estimate may be lower
for lighter athletes (i.e. 585 kg).
.Protein may act as more than simply substrate
to supply the building blocks for protein
synthesis and may be an important trigger to
affect phenotypic changes induced by exercise.
Leucine in particular occupies a prominent
position and may well be critical in enhancing
protein-mediated recovery and adaptation as
detailed above.
.The rate of digestion of purportedly nutritionally
equivalent proteins affects the response of MPS
and this appears to be linked to the amplitude
and the rate of rise in blood leucine to activate
key signalling proteins and turn on MPS.
.The optimum timing for protein ingestion to
promote the most favourable recovery and
adaptation is after exercise. While data do not
yet exist to define exactly how long a theoretical
‘‘window of anabolic opportunity’’ exists, it is
safest to state that athletes who are interested in
performance need to consume protein as soon
as possible after exercise.
.To optimize the ratio of fat-to-lean tissue mass
loss during hypoenergetic periods, athletes are
advised to ensure that they lower their carbohy-
drate intake to *40% of their energy intake
(with an emphasis on consumption of lower GI
carbohydrates), which usually means no more
than 3–4 g kg
71
day
71
, and increase their
protein intake to *20–30% of their energy
intake or *1.8–2.7 g kg
71
day
71
. Consid-
eration of how low carbohydrate intake should
go would be dictated by how much exercise
performance may be compromised by consum-
ing lower than recommended carbohydrates.
By engaging in resistance exercise during a
hypoenergetic dieting period, athletes will also
provide a markedly anabolic stimulus to retain
muscle protein. All of the aforementioned
strategies will, however, result in less absolute
weight loss than if protein is not increased and
resistive exercise is not performed, which may
be important for some athletes.
.There appears to be no evidence to recommend
the addition of carbohydrate to protein sources
to optimize the anabolic environment for
MPS. For endurance-trained athletes, the same
recommendation will quite likely enhance the
restoration of glycogen, which may be an
important consideration.
.An economical, practical, and efficacious
beverage for athletes to consume after exercise
is milk, particularly flavoured milk that con-
tains added simple sugar. For the athlete who
suffers from lactose maldigestion, there are a
number of practical options such as pre-treated
lactose reduced milk. This beverage provides
fluid that is better retained than water and
isotonic sport drinks, carbohydrate to restore
muscle glycogen, and high-quality proteins to
repair and facilitate adaptive changes in protein
synthesis.
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... 13 Dietary protein is essential for health, repair and re-modelling of damaged tissue following exercise and promoting adaptations. 14 Total protein intake is an important consideration for enhancing the muscle protein synthetic response and eventual fat free mass development 15,16 which can positively influence speed, power, endurance and agility. 17 Requirements for protein intake in athletes are broad (1.2-2.0 g·kg·d) 18,19 with no difficulty in meeting these requirements found in professional [20][21][22][23] and/or developmental rugby players. ...
... Ingesting adequate protein has long been recognised as a crucial consideration of dietary intake for athletes, with those engaging in team sports requiring substrates for training-induced protein re-modelling resulting in adaptations and to replace oxidised amino acids during prolonged exercise bouts. 15 Despite the average protein intake meeting requirements, large variability between individuals was apparent. During the monitoring period, two participants did not meet the 1.2 g·kg minimum threshold set by the International Society for Sports Nutrition and American College of Sports Medicine 18,19 and only three exceeded 1.6 g·kg·d, with greater protein intakes recommended for individuals when energy availability is low. ...
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Provincial academies represent an important bridge between amateur and professional level rugby union in New Zealand. Athletes are provided with professional-level coaching; however, limited direct nutrition support is available. Congested training schedules and the requirement to work or study due to a lack of financial support may present a challenge towards athletes meeting nutrition requirements. The aim of the study was to facilitate improvement in nutrient intake, body composition and subjective well-being in provincial academy athletes via the implementation of a nutrition-support protocol based around behaviour change techniques. Significant increases in total energy (pre: 2492 ± 762 kcal; post: 2614 ± 625 kcal), relative energy (pre: 24.4 ± 7.5 kcal·kg; 25.5 ± 6.0 kcal·kg), total protein (pre: 131.1 ± 41.8 g; 153.8 ± 37.1 g) and relative protein (pre: 1.3 ± 0.4 g·kg; post: 1.5 ± 0.3 g·kg) were observed. Furthermore, changes in subjective sleep quality, stress, mood and upper body soreness were observed following the intervention. No changes were observed in body composition, carbohydrate or fat intake. Significant variability in nutrition and body composition changes highlights the importance of applying an individualised approach to nutrition support provision in developmental athletes. Practitioners working within these environments should be aware of the challenges and influences contributing to athletes’ nutrition choices and habits.
... A growing body of literature has recommended a vegan diet for athletes engaged in weight class or aesthetic sports or any sports type in which weight is directly proportional to sports performance e.g swimming, where a vegan diet helps the athletes in maintaining decreased body mass and lean body type. A correlation between a vegan diet and reduced skinfold thickness and waist-to-hip ratio was found by Phillpset et al. [150] independent of weight loss. In another research, it was found that using lentils as post workout meal enhanced fatty acid oxidation due to its low glycemic response as compared to using post-workout diet containing potatoes and eggs. ...
... Therefore, inappropriately balanced macro and micronutrient composition of vegan diet may result in compromised strength performance. [150,155] There is limited literature available on the effect of vegan diet on muscular adaptability, the currently available literature reports the effect of important nutrients, like leucine, taurine, Docosahexaenoic acid (DHA), Eicosapentaenoic acid (EPA) and short-chain fatty acid (SCFA) on cell signaling in different tissues and can improve sports performance by long term following of different dietary patterns. [78,156,157] Moreover, dietary choices also affect gut microflora. ...
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Sportsmen may choose to include vegetarian diet in their dietary regime for a variety of ways like its beneficial health impact, due to religious restrictions or to protect animals for environmental integrity. These diets are loaded with a wide variety of phytochemicals with superior health benefits safeguarding against chronic diseases. Besides their role in health management these foods also play a key role in enhancing different sports performances owing to contained with instant energy providing carbohydrates that are crucial for competitive sports performance. Furthermore, they are also richly enriched with antioxidants that are essential for high-end sports performance. However, few vegetarian diets are the source of anti-nutritional entities like high fiber content, chelating agents, phytates, and tannic acid. These interfere with the bio-availability of crucial dietary components like iron, zinc, proteins. Therefore, a sound nutritional approach is required while planning plant-based dietary regimes for sports performance. This review will systematically focus on the impact of vegetarian diets on sports performance in the light of currently available research findings in this field to provide a guiding hand to sports specialists and nutritional experts in planning the vegetarian dietary plans for optimizing the sports performance. In addition, this review explains the bio-availability and enhancement strategies of different vegetarian diet-based nutrients through different energy metabolism pathways.
... It is reported that a smaller surplus is required in resistance-trained athletes (+5-10% above maintenance) and more in sedentary individuals and resistance-training novices (+10-20% above maintenance), to optimize protein synthesis, minimizing the accumulation of adipose tissue [20]. However, for the FM reduction phase, it is necessary to generate an energy deficit, in which the protein dose should be increased to between 1.8 and 2.7 g·kg −1 BM·d −1 [21] or even 2.3 and 3.1 g·kg −1 BM·d −1 [22] so as not to generate loss in muscle tissue. CHOs have traditionally been used as the main energy source in strength training, with levels of between 3 and 7 g·kg −1 BM·d −1 [23]. ...
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Reviews focused on the ketogenic diet (KD) based on the increase in fat-free mass (FFM) have been carried out with pathological populations or, failing that, without population differentiation. The aim of this review and meta-analysis was to verify whether a ketogenic diet without programmed energy restriction generates increases in fat-free mass (FFM) in resistance-trained participants. We evaluated the effect of the ketogenic diet, in conjunction with resistance training, on fat-free mass in trained participants. Boolean algorithms from various databases (PubMed, Scopus. and Web of Science) were used, and a total of five studies were located that related to both ketogenic diets and resistance-trained participants. In all, 111 athletes or resistance-trained participants (87 male and 24 female) were evaluated in the studies analyzed. We found no significant differences between groups in the FFM variables, and more research is needed to perform studies with similar ketogenic diets and control diet interventions. Ketogenic diets, taking into account the possible side effects, can be an alternative for increasing muscle mass as long as energy surplus is generated; however, their application for eight weeks or more without interruption does not seem to be the best option due to the satiety and lack of adherence generated.
... In female athletes specifically, very limited research has been conducted on the protein requirements, but existing data suggest that active women should consume a minimum of 1.6 g/kg/day of protein [58]. Higher protein diets (> 2.0 g/kg/day) have been shown to be important for maintaining LM and resting energy expenditure under periods of intentional and unintentional caloric restriction [59], which may be more prevalent among active women. Additionally, high-protein diets (> 2.2 g/kg/ day) have not resulted in any adverse effects to bone mineral density or kidney function in healthy women after 6 months [60] or 1 year [61]. ...
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Women are the largest consumers of dietary supplements. Dietary supplements can play a role in health and performance, particularly for women. Growing evidence and innovations support the unique physiological and nutrient timing needs for women. Despite the need for more nutrition and exercise-specific research in women, initial data and known physiological differences between sexes related to the brain, respiration, bone, and muscle support new product development and evidence-based education for active women regarding the use of dietary supplements. In this narrative review, we discuss hormonal and metabolic considerations with the potential to impact nutritional recommendations for active women. We propose four potential areas of opportunity for ingredients to help support the health and well-being of active women, including: (1) body composition, (2) energy/fatigue, (3) mental health, and (4) physical health.
... While these diets are often, but not exclusively, associated with decreased risk for cancer (2)(3)(4), cardiometabolic diseases (3)(4)(5), diabetes (6), and obesity (7)(8)(9), the possibility of micronutrient inadequacies, including iron, vitamin B12, and vitamin D remain a concern. Furthermore, although energy intakes tend to be similar, protein intake is often significantly lower for vegetarians when compared to omnivores (10)(11)(12)(13)(14). This can be concerning as protein intakes are directly linked to muscle mass and strength (15)(16)(17). ...
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Full-text available
Growing numbers of Americans are adopting vegetarian or vegan diets. While risk for some chronic conditions may be lower when following these diets, concern remains over the ability to consume adequate amounts of various nutrients, notably, protein. Knowing that serum creatinine is a reliable marker of muscle mass, this study examined the relationships between serum creatinine, lean body mass (LBM), handgrip strength, and protein intake in healthy vegetarian (n = 55) and omnivorous (n = 27) adults. Significantly higher protein intakes (+31%), LBM (+7%), serum creatinine (+12%) and handgrip strength (+14%) were observed for the omnivore participants compared to vegetarian participants. Positive correlations (p < 0.001) were noted between creatinine and LBM (R2 = 0.42), creatinine and handgrip strength (R2 = 0.41), protein intake and LBM (R2 = 0.29), and handgrip strength and LBM (R2 = 0.69). These data show that serum creatinine concentrations were lower in vegetarian women and men in comparison to their omnivorous counterparts and that serum creatinine concentrations correlate with LBM and strength in healthy adults, regardless of diet.
... g.kg -1 .day -1 maximize muscle protein synthesis in athletes (Phillips and Van Loon 2011). The average values of protein ingested in this study seem adequate not only for muscle repair and accretion as well as for energetic purposes. ...
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Background: Sports performance, besides the mental and emotional features of the athlete, is the outcome from the correct combination of training load, rest/ recovery and nutrition. Nutritional deficits or excesses can be deleterious for sports performance, particularly in sports that rely on high power output as 1000m kayak paddler. Objective: To describe the nutritional intake habits of a highly performing kayaker, and its adequacy for training, as only few studies have focused on this type of sports. Methods: An elite male kayaker specialized in 1000m flat-water races, World Champion, European Champion and Silver medallist in the London Olympic Games (35 years) reported his food intake for 7 consecutive days during a specific preparation period. Results: Daily average energy intake was 3174 ± 306 kcal; the intake of carbohydrates was 47.8 ± 9.3% (4.4 ± 1.2 g.kg-1. body weight. day-1), protein 20.8 ± 4.3% (1.9 ± 0.3 g.kg-1body weight. day) and fat intake was 31.4 ± 5.2% (1.3 ± 0.2 g. kg-1 body weight day. d-1). Fiber average consumption was 23.6 ± 9.2 g/day and cholesterol 638 ± 218 g/day. While water-soluble vitamins were within the recommended levels, fat-soluble vitamins and beta-carotene were below athletes’ recommendations. All macro minerals intake was within the Dietary References Intake (DRI) for general population values as well as the trace elements with exception of iodine and molybdenum. Also, an unbalanced ratio between omega-6/omega-3 fatty acids was observed. Conclusion: This kayaker had a caloric intake adequate to the training requirement of the analyzed week. However, a reduction in fat intake and an increment in carbohydrate should be promoted in order to achieve dietary recommendations for athletes. The low intake of fat-soluble vitamins and beta-carotene found may justify the use supplementation. Keywords: kayaking, nutrition, macronutrients, vitamins, minerals
... Indeed, acute metabolic studies 19,24,34,35,[41][42][43] of muscle protein turnover, and longitudinal or interventional studies 28,44,45 of muscle mass and function, have used meat and dairy protein consumption in older adults as the crux of the current evidence base, and consequently undergird currently applied (and robust) dietary protein recommendations (eg, 17,32,33 ). However, rising (aging) populations 46 ; increased urbanization, affluence, and economic development 47,48 ; greater awareness of (increased) protein requirements in various populations (eg, athletes, older adults, weight management, clinical situations, etc.) 17,30,49,50 -among other factors-have converged to explain the rapidly (and presumably exponentially) increasing global consumption of dietary protein. 51 However, the nutritional evidence base for the efficacy of non-animal-derived proteins to support healthy muscle aging has not kept pace. ...
Article
Full-text available
To mitigate the age-related decline in skeletal muscle quantity and quality, and the associated negative health outcomes, it has been proposed that dietary protein recommendations for older adults should be increased alongside an active lifestyle and/or structured exercise training. Concomitantly, there are growing environmental concerns associated with the production of animal-based dietary protein sources. The question therefore arises as to where this dietary protein required for meeting the protein demands of the rapidly aging global population should (or could) be obtained. Various non-animal–derived protein sources possess favorable sustainability credentials, though much less is known (compared with animal-derived proteins) about their ability to influence muscle anabolism. It is also likely that the anabolic potential of various alternative protein sources varies markedly, with the majority of options remaining to be investigated. The purpose of this review was to thoroughly assess the current evidence base for the utility of alternative protein sources (plants, fungi, insects, algae, and lab-grown “meat”) to support muscle anabolism in (active) older adults. The solid existing data portfolio requires considerable expansion to encompass the strategic evaluation of the various types of dietary protein sources. Such data will ultimately be necessary to support desirable alterations and refinements in nutritional guidelines to support healthy and active aging, while concomitantly securing a sustainable food future.
... This finding is consistent with the fact that athletes, in response to their increased requirements to 350 meet different purposes, are more likely to consume higher amounts of dietary protein than their 351 healthy counterparts [41]. 352 ...
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The association between meal timing and energy and macronutrient intakes has to be more explored. To explore this potential relationship during Ramadan diurnal intermittent fasting (RDIF), a systematic review of the available literature assessing energy and macronutrient intakes before and during Ramadan was conducted. Studies that assessed energy, carbohydrates, protein, fats, fibers, and water were collected from ten scientific databases. Out of the 4776 studies identified, 85 studies (4594 participants aged 9-85 years) were solicited. The effect sizes were as follows: energy (K =80 53 studies, N =3343 participants, mean difference (MD) [95% confidence interval, CI] =-142.45 [-54 215.19;-69.71]), carbohydrates (K=75, N=3111, MD =-23.90 [-36.42;-11.38]), protein (K=74, 55 N=3108, MD =-4.21 [-7.34;-1.07]), fats (K=73, N=3058, MD =-2.03 [-5.73; 1.67]), dietary fibers 56 (K=16, N=1198, MD = 0.47 [-1.44; 2.39]), and water (K=17, N=772, MD =-350.80 [-618.09; 57 83.50]). Subgroup analyses revealed that age is the only significant moderator for the six dietary outcomes, while physical activity was the only significant moderator for water intake. Slight, but statistically significant reductions in energy, carbohydrate, and protein intakes were found during Ramadan. The change in meal timing rather than quantitative dietary intakes might induce various physiological and health effects of RDIF.
... Such practice was reported from most respondents (Figure 4). In the RWL period, the high protein intake of respondents is appropriate because it maximizes the maintenance of muscle mass and strength, improves regeneration, and reduces muscle microdamage [29][30][31]. Fats were avoided in the RWL period, as well as after weigh-in, and during the competition, which contributes to energy deficit in the RWL period and to easier digestion and reduction of the possibility of GI symptoms [3]. Higher consumption of vegetables (Figure 3), which are low in energy and high in nutritional value, is appropriate up to 3 days before weigh-in. ...
Article
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Background: Rapid weight loss (RWL) followed by rapid weight gain (RWG) is a regular pre-competition routine in combat sports and weightlifting. With the prevalence of these sports exceeding 20% at the 2020 Tokyo Olympics, there are limited data on RWL and RWG practices and their impact on well-being and competitive success in elite-level athletes. Methods: A total of 138 elite-level female and male judokas, 7.7% of the athletes ranked as top 150 on the International Judo Federation Senior World Ranking List (WRL), completed a survey on RWL, RWG, and the consequences of these practices. Results: Our findings showed that 96% of the respondents practice RWL. The average reduced body mass percentage was 5.8 ± 2.3%. Respondents who used either of the dehydration methods - fluid restriction, sauna suit, and/or sauna/hot bath - to reduce weight were 88%, 85%, and 76%, respectively. Furthermore, 91% of the respondents reported reduced energy as a negative consequence of RWL and 21% experienced a collapse episode during the RWL period. Respondents ranked 1-20 on the WRL experienced fewer negative consequences of RWL and RWG (p = 0.002) and had more dietitian and/or medical doctor support (p = 0.040) than lower-ranked respondents. Those who started with RWL practices before the age of 16 (38%) were ranked lower on the WRL (p = 0.004) and reported more negative consequences of RWL and RWG (p = 0.014). Conclusions: This study is the first to provide insight into the RWL practices of worldwide elite-level judokas and provides valuable information for the combat sports society, especially coaches. Proper weight management and optimal timed initiation of RWL practices in a judoka's career may contribute to success at the elite level.
Chapter
Meat consumption has been increasing around the globe despite the controversies surrounding its possible influence in health. It is recognized as a valuable source of protein, iron, and vitamin B12, but the role of fat and the fatty acid profile is frequently pointed out as a potential risk factor. Epidemiologic studies also have some incongruent results when considering processing and cooking methods, as well as meat cuts, in disease risk. This raises the importance of further clarifying the nutritive role of meat in human diet, as well as the possible associations between meat consumption and health risks, thus promoting effective and science-based public health messages. This chapter will present the nutritional composition of meat and the most relevant and recent evidence concerning the effects of its consumption in noncommunicable chronic diseases.
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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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The nature of the deficit underlying age-related muscle wasting remains controversial. To test whether it could be due to a poor anabolic response to dietary amino acids, we measured the rates of myofibrillar and sarcoplasmic muscle protein synthesis (MPS) in 44 healthy young and old men, of similar body build, after ingesting different amounts of essential amino acids (EAA). Basal rates of MPS were indistinguishable, but the elderly showed less anabolic sensitivity and responsiveness of MPS to EAA, possibly due to decreased intramuscular expression, and activation (phosphorylation) after EAA, of amino acid sensing/signaling proteins (mammalian target of rapamycin, mTOR; p70 S6 kinase, or p70(S6k); eukaryotic initiation factor [eIF]4BP-1; and eIF2B). The effects were independent of insulin signaling since plasma insulin was clamped at basal values. Associated with the anabolic deficits were marked increases in NFkappaB, the inflammation-associated transcription factor. These results demonstrate first, EAA stimulate MPS independently of increased insulin availability; second, in the elderly, a deficit in MPS in the basal state is unlikely; and third, the decreased sensitivity and responsiveness of MPS to EAA, associated with decrements in the expression and activation of components of anabolic signaling pathways, are probably major contributors to the failure of muscle maintenance in the elderly. Countermeasures to maximize muscle maintenance should target these deficits.
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This paper compares the efficacy of two widely used weight-loss diets differing in macronutrient composition - a low-carbohydrate diet versus a low-fat diet. Although "a calorie is a calorie" under the controlled conditions of a metabolic unit (i.e., only the level of calorie intake matters and not the source of calories), we conclude that these interrelationships are far more complex in the free-living situation. The different diet-related factors that condition energy balance, including total energy intake, satiety and hunger sensory triggers, and palatability, must be considered when assessing the efficacy of weight-reducing diets of different macronutrient composition.
Book
Part of the authoritative series on reference values for nutrient intakes , this new release establishes a set of reference values for dietary energy and the macronutrients: carbohydrate (sugars and starches), fiber, fat, fatty acids, cholesterol, protein, and amino ...
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Amino acids act to regulate multiple processes related to gene expression, including modulation of the function of the proteins that mediate messenger RNA (mRNA) translation. By modulating the function of translation initiation and elongation factors, amino acids regulate the translation of mRNA on a global scale and also act to cause preferential changes in the translation of mRNAs encoding particular proteins or families of proteins. However, amino acids do not directly regulate the function of translation initiation and elongation factors, but instead modulate signaling through pathways traditionally considered to be solely involved in mediating the action of hormones. The best-characterized example of amino acid-induced regulation of a signal transduction pathway is one involving a protein kinase referred to as the mammalian target of rapamycin (mTOR), through which the branched-chain amino acids, particularly leucine, act to modulate the function of proteins engaged in both global mRNA translation and the selection of specific mRNAs for translation. Less understood at this point in time is evidence suggesting that amino acids also act to regulate mRNA translation through mTOR-independent mechanisms. The goal of the present review is to briefly summarize studies, primarily those performed in the laboratories of the authors, that focus on the role of the branched-chain amino acids in the regulation of mRNA translation in skeletal muscle.
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It is unclear whether low-carbohydrate, high-protein, weight-loss diets benefit body mass and composition beyond energy restriction alone. The objective was to use meta-regression to determine the effects of variations in protein and carbohydrate intakes on body mass and composition during energy restriction. English-language studies with a dietary intervention of > or =4200 kJ/d (1000 kcal/d), with a duration of > or =4 wk, and conducted in subjects aged > or =19 y were considered eligible for inclusion. A self-reported intake in conjunction with a biological marker of macronutrient intake was required as a minimum level of dietary control. A total of 87 studies comprising 165 intervention groups met the inclusion criteria. After control for energy intake, diets consisting of < or =35-41.4% energy from carbohydrate were associated with a 1.74 kg greater loss of body mass, a 0.69 kg greater loss of fat-free mass, a 1.29% greater loss in percentage body fat, and a 2.05 kg greater loss of fat mass than were diets with a higher percentage of energy from carbohydrate. In studies that were conducted for >12 wk, these differences increased to 6.56 kg, 1.74 kg, 3.55%, and 5.57 kg, respectively. Protein intakes of >1.05 g/kg were associated with 0.60 kg additional fat-free mass retention compared with diets with protein intakes < or =1.05 g/kg. In studies conducted for >12 wk, this difference increased to 1.21 kg. No significant effects of protein intake on loss of either body mass or fat mass were observed. Low-carbohydrate, high-protein diets favorably affect body mass and composition independent of energy intake, which in part supports the proposed metabolic advantage of these diets.