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Br J Sports Med 2012;46:618–620. doi:10.1136/bjsports-2012-
091198618
Nutritional supplement series
INTRODUCTORY REMARKS
Quercetin was fi rst introduced to our A–Z series
in the article on fl avonoids.1 In Part 33, the author
of the fl avonoid review, Dr Nieman, updates this
topic. We also cover another intriguing plant-
based compound with proposed benefi ts as an
antioxidant and stimulator of mitochondrial bio-
genesis, resveratrol. Rhodiola rosea, a claimed adap-
togen, concludes this issue.
QUERCETIN
D C Nieman
Epidemiological studies support multiple disease
prevention benefi ts for individuals consuming foods
rich in the fl avonol quercetin. In vitro and animal
studies indicate that quercetin is a strong antioxi-
dant and anti-infl ammatory agent, and exerts anti-
pathogenic and immune regulatory infl uences.2
Quercetin supplementation studies in community-
dwelling humans do not refl ect these positive bene-
fi ts, but research is continuing in order to determine
the proper outcome measures, dosing regimen and
adjuvants that may amplify any perceived bioactive
effects of quercetin in vivo.
Quercetin supplementation studies in athletes
have focused on potential infl uences on post-exer-
cise infl ammation, oxidative stress and immune
dysfunction, illness rates following periods of
physiological stress and exercise performance.

Results thus far have been negative for quer-
cetin’s countermeasure effects on postexercise
physiological stress indicators, such as immune
perturbations.3–5 However, when quercetin sup-
plementation is combined with other polyphenols
and food components such as green tea extract,
isoquercetin and fi sh oil, a substantial reduction
in exercise-induced infl ammation and oxidative
stress occurs in athletes, with augmentation of
innate immune function.6
Quercetin exerts strong antiviral activities when
cultured with a wide variety of pathogens. In mice,
quercetin supplementation for 7 days before inoc-
ulation with infl uenza virus and a 3-day period
of heavy exertion partially reduced the exercise-
induced increase in morbidity and mortality.7
A 12-week community trial showed a modest
reduction in upper respiratory tract infections
(URTI) among physically active subjects between
the ages of 40 and 85 years consuming 1000 mg
quercetin per day, but not among younger adults.8
Cyclists randomised to 1000 mg/day quercetin or
placebo for fi ve weeks experienced reduced URTI
incidence during the two-week period following
three days of exhaustive exercise.3
Quercetin supplementation over 7 days induces
an increase in mitochondrial biogenesis and tread-
mill endurance performance (37%) and running
distance in wheels in mice.9 The quercetin-related
effects on performance in untrained humans are
modest and far below those reported in mice.10
About 10 different exercise studies have been con-

ducted and, despite confl icting results regarding
the effect of quercetin supplementation on endur-
ance exercise capacity, a meta-analysis indicated
an ergogenic effect which the authors described as
being between trivial and small (~3%) but which
was signifi cant.11 12
Future research should emphasise multiple types
of performance measures, longer supplementa-
tion periods in humans and combined ingestion
with adjuvants that might augment any bioac-
tive effects of quercetin in exercise. The potential
synergism between initiation of exercise training
and quercetin supplementation should be studied
to determine if untrained subjects achieve ampli-
fi ed performance outcomes. In general, querce-
tin’s bioactive effects support athletic endeavour,
but additional research is needed to defi ne better
the optimal dosing regimen and adjuvants that
might amplify benefi ts during heavy training and
competition.
RESVERATROL
M W Laupheimer
Resveratrol is a natural polyphenolic fl avonoid
antioxidant which may provide numerous health
benefi ts such as the prevention of cancer, cardio-
vascular disease and ischaemic injuries, as well as
enhancing stress resistance.13 14 It is a freely avail-
able food supplement and is found in the seeds
and skins of grapes, red wine, mulberries, peanuts
and rhubarb.13 14
Interest in resveratrol in sports medicine arose
after animal studies assessed endurance perfor-
mance of mice and found a dose-dependent increase

in exercise tolerance, improved motor skills and
increased number and activity of mitochondria in
muscle cells. Resveratrol-treated mice had a sig-
nifi cantly higher maximum VO2 rate, suggestive of
an increased oxidative capacity. Resveratrol intake
increases the ratio of oxidative to non-oxidative
type muscle fi bres and increases muscle strength
1Human Performance
Laboratory, Appalachian State
University, Kannapolis, North
Carolina, USA
2Department of Sport and
Exercise Medicine, Queen
Mary Hospital, University of
London, London, UK
3Department of Sport,
Faculty of Health & Wellbeing,
Sheffi eld Hallam University,
Sheffi eld, UK
4Australian Institute of Sport,
Canberra, Australia
5Performance Infl uencers
Limited, London, UK
6Green Templeton College,
University of Oxford, UK
Correspondence to
L M Castell, Green Templeton
College, University of Oxford,
Oxford OX2 6HG, UK;
[email protected]
Received 20 March 2012
Accepted 20 March 2012
A–Z of nutritional supplements: dietary supplements,

sports nutrition foods and ergogenic aids for health
and performance—Part 33
D C Nieman,1 M W Laupheimer,2 M K Ranchordas,3 L M
Burke,4
S J Stear,5 L M Castell6
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091198 619
in resveratrol-treated mice.15 The resveratrol effects also seem
to be dependent on the length of intake, as one of the actions
proposed is a gene switch.16
There are no established doses for resveratrol but Kennedy
(2010) showed in humans that resveratrol administration with
doses of 250 mg and 500 mg, resulted in a dose-dependent
increase in cerebral blood fl ow during task performance and
enhanced oxygen extraction.17 Doses of 1600 mg per day
in a 70 kg participant are regarded as safe,13-15 even long
term.18
Resveratrol as a food supplement in sports medicine has
not received much attention despite some basic scientifi c
evidence that this substance could have multiple indications
related to high-performance sports. Therefore, further studies
are required to confi rm whether there are similar effects in
humans.

RHODIOLA ROSEA
M K Ranchordas
R rosea is a herb part of the Crassulacae family and is also
known
as Arctic root, rose root and golden root. It grows in the moun-
tainous and Arctic regions of North America, Europe and
Asia.19
It is purported that R rosea possesses several ergogenic prop-
erties such as increasing physical and mental performance,20
enhancing cognitive and neural function21 and free radical
mitigation.22 It has been described as an adaptogen because of
its cardioprotective effects.23
Although the majority of research investigating the effects
of R rosea has been conducted in the animal model, there have
been several studies done in humans. The dosages investigated
in humans have ranged from 100 to 600 mg/day. Studies inves-
tigating its effects on exercise performance have been mixed.
R rosea supplementation in doses of 100 mg/day for 20 days and
one acute dose of 200 mg/day were found to improve endurance
exercise capacity by 6.5% and 5.0%, respectively.21 24
However,
other studies have found no positive effects on VO2peak, peak
power, lactate threshold25 and ventilatory threshold.26
Studies investigating R rosea supplementation on neural and
cognitive performance have also produced mixed results.
Doses of 100–555 mg/day have found positive effects on cog-
nition21 27 28 but other studies have found no effect using
doses
200 mg/day either acutely or for 5 weeks.24 R rosea contains
phenylopopropanoids, phenolic compounds and fl avonoids;
some studies have found that supplementation can increase
antioxidant levels29 decrease muscle-damage markers20 and
mitigate free radicals.22
Based on the available literature, it remains unclear whether

R rosea supplementation in doses of 100–600 mg/day can
enhance either mental and/or exercise performance. However,
there is some evidence that R rosea does possess antioxidant
properties. Further tightly controlled studies in well-trained
athletes need to be conducted in order to determine any per-
formance-enhancing effects.
CONCLUDING COMMENTS
In summary, all three products show potential, both in vitro
and in animal models, of properties ranging from antioxidant
activity to regulation of cell signalling. However, particularly
in the cases of quercetin and resveratrol, there is evidence of
species differences and reduced translation of benefi ts seen
in rodents to well-trained humans. Further work is needed
to determine whether these compounds actually enhance
athletic performance. Nevertheless, there is a strong interest
in investigating protocols in which a cocktail of these phy-
tochemicals might work synergistically.
Competing interests David C Nieman is on the Scientifi c
Advisory Board for
Quercegen Pharma; this research has also been funded by Coca
Cola.
Provenance and peer review Commissioned; not externally peer
reviewed.
REFERENCES
1. Nieman DC, SJ Stear SJ, Castell LM, et al. A–Z of
nutritional supplements:
dietary supplements, sports nutrition foods and ergogenic aids
for health and
performance: part 15. Br J Sports Med 2010;44:1202–205

2. Boots AW, Haenen GR, Bast A. Health effects of quercetin:
from antioxidant to
nutraceutical. Eur J Pharmacol 2008;585:325–37.
3. Nieman DC, Henson DA, Gross SJ, et al. Quercetin reduces
illness but
not immune perturbations after intensive exercise. Med Sci
Sports Exerc
2007;39:1561–9.
4. Nieman DC, Henson DA, Davis JM, et al. Quercetin
ingestion does not alter
cytokine changes in athletes competing in the Western States
Endurance Run.
J Interferon Cytokine Res 2007;27:1003–11.
5. Konrad M, Nieman DC, Henson DA, et al. The acute effect
of ingesting a
quercetin-based supplement on exercise-induced infl ammation
and immune
changes in runners. Int J Sport Nutr Exerc Metab 2011;21:338–
46.
6. Nieman DC, Henson DA, Maxwell KR, et al. Effects of
quercetin and EGCG
on mitochondrial biogenesis and immunity. Med Sci Sports
Exerc 2009;41:
1467–75.
7. Davis JM, Murphy EA, McClellan JL, et al. Quercetin
reduces susceptibility to
infl uenza infection following stressful exercise. Am J Physiol
Regul Integr Comp
Physiol 2008;295:R505–9.
8. Heinz SA, Henson DA, Austin MD, et al. Quercetin

supplementation and upper
respiratory tract infection: A randomized community clinical
trial. Pharmacol Res
2010;62:237–42.
9. Davis JM, Murphy EA, Carmichael MD, et al. Quercetin
increases brain and
muscle mitochondrial biogenesis and exercise tolerance. Am J
Physiol Regul Integr
Comp Physiol 2009;296:R1071–7.
10. Nieman DC, Williams AS, Shanely RA, et al. Quercetin’s
infl uence on exercise
performance and muscle mitochondrial biogenesis. Med Sci
Sports Exerc
2010;42:338–45.
11. Kressler J, Millard-Stafford M, Warren GL. Quercetin and
endurance exercise
capacity: a systematic review and meta-analysis. Med Sci Sports
Exerc
2011;43:2396–404.
12. Goulet ED. Quercetin supplementation and endurance
exercise capacity: a
comment. Med Sci Sport Exerc 2012;44:556.
13. Baur JA, Sinclair DA. Therapeutic potential of resveratrol:
the in vivo evidence.
Nat Rev Drug Discov 2006;5:493–506.
14. Markus MA, Morris BJ. Resveratrol in prevention and
treatment of common
clinical conditions of aging. Clin Interv Aging 2008;3:331–9.
15. Lagouge M, Argmann C, Gerhart-Hines Z, et al. Resveratrol

improves
mitochondrial function and protects against metabolic disease
by activating SIRT1
and PGC-1alpha. Cell 2006;127:1109–22.
16. Murase T, Haramizu S, Ota N, et al. Suppression of the
aging-associated decline
in physical performance by a combination of resveratrol intake
and habitual
exercise in senescence-accelerated mice. Biogerontology
2009;10:423–34.
17. Kennedy DO, Wightman EL, Reay JL, et al. Effects of
resveratrol on cerebral
blood fl ow variables and cognitive performance in humans: a
double-blind,
placebo-controlled, crossover investigation. Am J Clin Nutr
2010;91:1590–7.
18. Juan ME, Vinardell MP, Planas JM. The daily oral
administration of high doses
of trans-resveratrol to rats for 28 days is not harmful. J Nutr
2002;132:
257–60.
19. Brown RP, Gerbarg PL, Ramazanov Z. Rhodiolo rosea: a
phytomedicinal
overview. HerbalGram 2002;56:40–52.
20. Abidov M, Crendal F, Grachev S, et al. Effect of extracts
from Rhodiola rosea
and Rhodiola crenulata (Crassulaceae) roots on ATP content in
mitochondria of
skeletal muscles. Bull Exp Biol Med 2003;136:585–7.
21. Spasov AA, Wikman GK, Mandrikov VB, et al. A double-

blind, placebo-controlled
pilot study of the stimulating and adaptogenic effect of
Rhodiola rosea SHR-5
extract on the fatigue of students caused by stress during an
examination period
with repeated low-dose regimen. Phytomedicine 2000;7:85–9.
22. De Sanctis R, De Bellis R, Scesa C, et al. In vitro protective
effect of Rhodiola
rosea extract against hypochlorous acid-induced oxidative
damage in human
erythrocytes. Biofactors 2004;20:147–59.
23. Maslova LV, Kondrat’ev BIu, Maslov LN, et al. The
cardioprotective and
antiadrenergic activity of an extract of Rhodiola rosea in stress.
Eksp Klin Farmakol
1994;57:61–3.
24. De Bock K, Eijnde BO, Ramaekers M, et al. Acute Rhodiola
rosea intake
can improve endurance exercise performance. Int J Sport Nutr
Exerc Metab
2004;14:298–307.
091198.indd 619 5/26/2012 2:44:19 PM5/26/2012 2:44:19
PM
091198620

25. Earnest CP, Morss GM, Wyatt F, et al. Effects of a
commercial herbal-based
formula on exercise performance in cyclists. Med Sci Sports
Exerc 2004;36:504–9.
26. Colson SN, Wyatt FB, Johnston DL, et al. Cordyceps
sinensis- and Rhodiola
rosea-based supplementation in male cyclists and its effect on
muscle tissue
oxygen saturation. J Strength Cond Res 2005;19:358–63.
27. Darbinyan V, Kteyan A, Panossian A, et al. Rhodiola rosea
in stress induced
fatigue–a double blind cross-over study of a standardized
extract SHR-5 with
a repeated low-dose regimen on the mental performance of
healthy physicians
during night duty. Phytomedicine 2000;7:365–71.
28. Shevtsov VA, Zholus BI, Shervarly VI, et al. A randomized
trial of two different
doses of a SHR-5 Rhodiola rosea extract versus placebo and
control of capacity
for mental work. Phytomedicine 2003;10:95–105.
29. Skarpanska-Stejnborn A, Pilaczynska-Szczesniak L, Basta
P, et al. Effects of
oral supplementation with plant superoxide dismutase extract on
selected redox
parameters and an infl ammatory marker in a 2,000-m rowing-
ergometer test.
Int J Sport Nutr Exerc Metab 2011;21:124–34.
091198.indd 620 5/26/2012 2:44:19 PM5/26/2012 2:44:19
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091100454
INTRODUCTORY REMARKS
The letter P brings together two of the most talked
about supplement families: proteins, which have
been perennially popular since the time of the
ancient Olympians and prohormones, which will
be dealt with in a later issue. Both supplement
families include products which range from simple
and relatively inexpensive, to exotic, expensive and
emotively marketed. Part 32 also includes informa-
tion on proline, a non-essential amino acid which is
marketed for growth and repair of soft tissue based
on its importance in the make-up of collagen.
PROTEIN
S M Phillips L Breen
Skeletal muscle protein turnover rates are
~1%–2%/d and exist in dynamic, usually balanced,
equilibrium between muscle protein breakdown
(MPB) and muscle protein synthesis (MPS). For
example, in the fasted state, MPB>MPS, whereas
in response to ingestion of protein-containing
meals, MPS>MPB.1 Thus, in healthy adults, mus-
cle mass remains relatively stable due to ‘fed-gain’
being balanced by fasted-loss, so daily protein
fl ux, while it may be 3–4 times greater than net
intake and loss, is in tight balance. Fasted-state
protein losses are typically about 40– 60 g/d for

a sedentary person weighing 70–90 kg and it is
debatable what the losses would be in athletes,
be they aerobically or resistance trained. Dietary
protein for athletic populations can serve as signal
and substrate for MPS, resulting in protein accre-
tion for hypertrophy, repair of damaged proteins
or assisting the maintenance of lean mass. There
are important messages for athletes, who differ
from sedentary individuals, in terms of quantity,
timing and quality of protein intake in relation
to an athlete’s training stimulus. The molecular
changes underpinning these adaptations are gene
transcription and mRNA translational signalling
and are highlighted in a review.2
The general consensus is that adults need
no more than 0.8–0.9 g/kg/d of protein to meet
their needs. However, the notion of consumption
of ‘extra’ protein above these levels to cover the
needs of increased physical activity is not con-
sidered. Dietary guidelines for athletes typically
recommend protein intakes of 1.2–1.7 g/kg/d,3 4
based on maintaining nitrogen (ie, protein) bal-
ance. By all accounts, nitrogen balance is a fl awed
method, measuring the minimum amount of
protein required to balance losses. Given the
functional demands of training and performance,
an optimal protein intake for athletes might exist
beyond merely satisfying a minimal requirement
and thus being in nitrogen balance. Indeed, pro-
tein intakes of 0.86 g/kg/d have been shown to
reduce whole-body protein synthesis rates in
strength-trained athletes,5 suggesting that cur-
rent recommendations for athletes may be insuf-
fi cient if synthetic rates of proteins are adversely

affected. Recently, Moore et al6 demonstrated a
protein dose response following resistance exer-
cise. Specifi cally, resistance exercise-induced MPS
increased in a curvilinear fashion with ingestion
of graded amounts of isolated egg protein, reach-
ing a plateau at 20 g, with no further increase at
40 g of protein. The amino acids supplied beyond
20 g of postexercise protein were not assimilated
into new muscle protein but instead were directed
toward oxidation.6 Interestingly, 10 g of essential
amino acids (EAA), equivalent to 25 g of most
high-quality intact protein, has been shown to
maximally stimulate MPS at rest also.7
There is no clear consensus as to whether pro-
tein ingestion before, during or after exercise
promotes the greatest adaptive response. With
respect to pre-exercise feeding, acute8 9 and long-
term studies,10 comparing pre- and post-training
protein feeding have yielded equivocal results.
Consumption of protein during exercise may
serve to provide amino acids required to improve
protein balance during and after exercise.11–13
However, in these studies,11–13 carbohydrate and
amino acids were provided: given the profound
impact of insulin for the suppression of MPB,14
it may be that the greater net balance is simply
an artefact of energy intake suppressing MPB and
not a protein-mediated rise in MPS. In addition to
adaptation, ingestion of additional protein dur-
ing endurance exercise does not improve perfor-
mance, reduce proxy markers of muscle damage
or hasten the recovery of muscle function.15
The potency of postexercise protein ingestion
for potentiating MPS is unequivocal.16 After exer-

cise, the energy status of the cell is returning to
resting levels, signalling that pathways are still
active, the muscle is prone to greater rates of MPS,
and all of these effects are enhanced with feeding.
Resistance exercise specifi cally targets a synthetic
response of myofi brillar proteins, it is therefore
not surprising that protein ingestion augments
this response.17 Interestingly, protein ingestion
1Department of Kinesiology,
McMaster University,
Hamilton, Canada
2Department of Nutritional
Sciences, Rutgers, The State
University, New Brunswick,
New Jersey, USA
3Australian Institute of Sport,
Canberra, Australia
4Performance Infl uencers
Limited, London, UK
5Green Templeton College,
University of Oxford,
Oxford, UK
Correspondence to
LM Castell, Green Templeton
College, University of Oxford,
Oxford, OX2 6HD, UK;
[email protected]
Received 22 February 2012
Accepted 22 February 2012
A to Z of nutritional supplements: dietary
supplements, sports nutrition foods and ergogenic
aids for health and performance—Part 32
S M Phillips,1 L Breen,1 M Watford,2 L M Burke,3 S J Stear,4

L M Castell5
091100.indd 454 4/4/2012 4:31:08 PM4/4/2012 4:31:08 PM
091100 455
route, it is not known how much body proline is derived from
the diet or made de novo. Since proline and hydroxyproline
(formed post-translationally) comprise approximately 25% of
the amino acids in collagen, proline is important to skin, bone,
cartilage, tendons, ligaments and connective tissues.30 Proline
is degraded via proline oxidase (dehydrogenase) to glutamate
or ornithine,29 31 32 and the fi nal fates include polyamines,
arginine and entry into the TCA cycle. Proline is an osmo-
protectant, a source of superoxide (in the immune system),
and plays a role in sensing both energy availability and main-
taining protein homeostasis. Hydroxyprolines are present in
proteins other than collagen where they play a role in oxygen
sensing while hydroxyproline, released from protein degrada-
tion, is an antioxidant.
Given the importance of proline in growth and wound repair,
including the muscle hypertrophy of training, it has been pro-
posed that proline may be conditionally essential. Indeed,
proline
has been marketed as a supplement for bodybuilders and weight
lifters, and for recovery after strenuous exercise. However,
there
is no direct evidence to support these claims. It is notable that,

while circulating proline concentrations decrease during burn
injury, dietary supplementation with proline has no effect on
plasma proline levels in such patients. Very few studies have
looked directly at proline supplementation,29 though in patients
with gyrate atrophy, supplements of up to 488 mg/kg/d are well
tolerated. It is, however, not possible to make any claims about
the safety or even effectiveness of proline supplements due to
an almost complete lack of data.29 33 An alternative approach
to increase proline availability would be to provide proline pre-
cursors (glutamine, ornithine, arginine) as dietary supplements
but again there is little evidence that these are effective or even
result in increased proline synthesis.30
Concluding comments
Proteins are clearly here to stay, although there is still some
debate about whether it is best to give protein supplementation
pre- or postexercise. Our authors have summarised the effects
of protein on performance in a useful strategy table. In particu-
lar, they emphasise the importance of consuming proteins as
soon as possible after exercise. High-quality proteins include
soya, milk and eggs, which means that the vegetarian athlete is
also able to access a good source of protein. There is little or no
evidence to support the claims that proline is helpful to weight-
lifters. In addition, almost nothing is known about the safety
of proline supplementation. The studies undertaken so far on
proline have been almost exclusively in clinical situations.
Competing interests None.
Provenance and peer review Commissioned; not externally peer
reviewed.
REFERENCES
1. Bohé J, Low A, Wolfe RR, et al. Human muscle protein
synthesis is modulated by

extracellular, not intramuscular amino acid availability: a dose-
response study.
J Physiol (Lond) 2003;552:315–24.
2. Sarbassov DD, Ali SM, Sabatini DM. Growing roles for the
mTOR pathway.
Curr Opin Cell Biol 2005;17:596–603.
3. Tarnopolsky MA, MacDougall JD, Atkinson SA. Infl uence
of protein intake
and training status on nitrogen balance and lean body mass. J
Appl Physiol
1988;64:187–93.
4. Lemon PW, Tarnopolsky MA, MacDougall JD, et al. Protein
requirements and
muscle mass/strength changes during intensive training in
novice bodybuilders.
J Appl Physiol 1992;73:767–75.
5. Tarnopolsky MA, Atkinson SA, MacDougall JD, et al.
Evaluation of protein
requirements for trained strength athletes. J Appl Physiol
1992;73:1986–95.
6. Moore DR, Robinson MJ, Fry JL, et al. Ingested protein dose
response of
muscle and albumin protein synthesis after resistance exercise
in young men.
Am J Clin Nutr 2009;89:161–8.
also potentiates the acute muscle protein synthetic response

to endurance exercise.18 Surprisingly, despite acute increases
in mitochondrial protein synthesis with endurance exercise,19
protein ingestion following a prolonged cycle did not poten-
tiate this response, but instead increased the synthesis of
myofi brillar proteins.20 Thus, protein ingestion may assist in
maintaining muscle structural integrity and power-generating
capacity, rather than infl uencing muscle aerobic capacity.
High volume resistance exercise appears to sensitise the
muscle to amino acid provision21 beyond the so called ‘window
of opportunity’; a period thought to induce the greatest muscle
anabolic effect.22 Thus, while there is some debate about the
critical nature of the timing of postexercise protein consump-
tion, we recommend that the sooner athletes consume pro-
tein after exercise the better. In addition, relatively frequent
protein ingestion (ie, every 3–4 h) over 24 h after exercise to
sustain the elevation in MPS is also recommended.
A protein digestibility corrected amino acid score close to
1.0 is defi ned as ‘high quality’. This includes animal protein
sources such as milk (composed of whey and casein protein),
eggs, isolated soya protein and most meats. Habitual con-
sumption of high-quality protein sources has a pronounced
effect on muscle recovery and adaptation. For example, milk
proteins result in a pronounced increase in MPS after resis-
tance exercise, compared with equivalent amounts of isolated
soya protein23 which, over time, promotes greater hypertro-
phy24 and is likely to be due to the whey protein constituent
in milk. Whey proteins stimulate greater rates of MPS over
isonitrogenous amounts of casein and soy protein at rest and
after exercise.25 The mechanisms underpinning the anabolic
advantage of whey protein are not entirely clear, but maybe
due to the relative amount of the branched-chain amino acids,
in particular, leucine. Leucine occupies a position of promi-
nence in that it alone can act as a stimulatory signal for MPS.26
Milk proteins and whey, in particular, are highly enriched

with leucine. More importantly perhaps, the rapid absorption
kinetics of whey proteins (or hydrolysed ‘slow’ digested pro-
teins) induces a greater rate of leucine appearance in the circu-
lation than soy and casein proteins and may be important for
stimulating MPS.27 28 Thus, although rapid leucinemia may be
important in activating MPS, provision of other EAAs may be
required to sustain the anabolic response.
Summary
Based on the current evidence, the following strategies are pro-
posed which should be very effective at allowing repair, remod-
elling and adaptation, and gains in lean mass in athletes:
Daily intakes higher than the RDA (1.2–1.6 g/kg/d). ▶
Emphasise dairy source proteins enriched in leucine. ▶
Consume protein in doses of 20–25 g/serving to maximise ▶
adaptive responses.
Equally spaced protein meals throughout the day. ▶
Consumption of protein immediately after exercise. ▶
PROLINE
M Watford L M Castell
Proline is not considered essential in adult humans, although
early work demonstrated a potential benefi t of proline when
arginine was limiting. Proline is readily available in dairy,
meat and eggs, and most plant proteins but can also be synthe-
sised endogenously by two pathways, one arising from orni-
thine and arginine, or one from glutamine and glutamate.29
Although the glutamate pathway is considered to be the major
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091100456
7. Cuthbertson D, Smith K, Babraj J, et al. Anabolic signaling
defi cits underlie
amino acid resistance of wasting, aging muscle. FASEB J
2005;19:422–4.
8. Tipton KD, Elliott TA, Cree MG, et al. Stimulation of net
muscle protein synthesis
by whey protein ingestion before and after exercise. Am J
Physiol Endocrinol
Metab 2007;292:E71–6.
9. Tipton KD, Rasmussen BB, Miller SL, et al. Timing of
amino acid-carbohydrate
ingestion alters anabolic response of muscle to resistance
exercise. Am J Physiol
Endocrinol Metab 2001;281:E197–206.
10. Cribb PJ, Hayes A. Effects of supplement timing and
resistance exercise on
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