Dietary Protein Requirements of athletes.pdf

The University of Sydney Page 1
DIETARY PROTEIN
REQUIREMENTS OF
ATHLETES
Dr Helen Parker, APD
Exercise and Sport Science
University of Sydney
Acknowledgements: Dr Janelle Gifford, Associate Professor
Helen O’Connor, Ms Alison Miles

– Context, setting the scene
– Protein metabolism during exercise
– Timing and type of protein, other factors
– Excessive and low intakes
– Recommendations
Outline
https://www.trailrun.es/media/cache/article_middle/upload/images/article/1671/article-pautas-mejorar-relacion-entrenamiento-nutricion-5784a40a8767a.jpg

Part 1: Context, setting the scene

Brief history of bodybuilding
Calculate The Grecian Ideal
http://www.bodybuilding.com/fun/drobson207.htm
Milos of Croton & Progressive
Resistance Training
Discus Thrower - circa 460 B.C.
http://www.crystalinks.com/greekart.html
http://www.healthfitnessrevolution.com/samir-trains-his-
strength-like-ancient-greek-athlete-milo-of-croton/
https://physicalculturestudy.com/2015/09/08/train-like-a-
sandow/
Late 1800’s Eugene Sandow
‘Father of Modern
Bodybuilding’
https://en.wikipedia.org/wiki/Arnold_Schwarzenegger
Arnold Schwartzenegger,
Mr Olympia 1974 entrant
Mitchell, L.; Hackett, D.; Gifford, J.; Estermann, F.; O'Connor, H. Do bodybuilders use evidence-based nutrition strategies to manipulate physique? Sports (Basel,
Switzerland) 2017, 5; DOI: 10.3390/sports5040076.
Spendlove, J.; Mitchell, L.; Gifford, J.; Hackett, D.; Slater, G.; Cobley, S.; O'Connor, H. Dietary intake of competitive bodybuilders. Sports Med 2015, 45, 1041-
1063; DOI: 10.1007/s40279-015-0329-4.

https://www.theatlantic.com/health/archive/2014/08/drugs-and-the-evolution-of-bodybuilding/375100/

Evolution of physique in swimming
Dawn Fraser
Olympian 1956, 1960, 1964
Shane Gould 1972
5 Olympic Medals
Libby Trickett
Olympic gold medallist
2004, 2008, 2012
http://olympics.com.au/news/fraser-joins-tokyo-celebrations-
50-years-after-historic-swim
https://www.gettyimages.co.uk/photos/shane-gould?page=2
https://www.girlswithmuscle.com/432379/Libby-Lenton---Trickett

Protein - RDI
 RDI – 0.84g/kg/day (males 19-70), 0.75g/kg/day (females 19-70)
 RDI – “... intake level sufficient to meet the nutrient requirements of nearly all
(97-98%) healthy individuals within an age/gender group” (NHMRC, 2017;
http://www.nrv.gov.au/).
 Reminder...the RDI is a level of nutrient intake that should be
adequate for most individuals.
 Athletes are not looking for ‘‘adequate’’ intake; they want
optimal intake.
See http://www.nrv.gov.au/
https://www.eatforhealth.gov.au/nutrient-reference-values/chronic-disease/macronutrient-
balance
https://www.eatforhealth.gov.au/nutrient-reference-values/nutrients/protein

Food sources of protein
– Meats and alternatives:
– Lean meats, poultry, fish
– Eggs
– Tofu
– Nuts, seeds
– Legumes/beans
– Dairy:
– Milk
– Yoghurt
– Cheese
– Dairy alternatives

RDI is not a ‘‘requirement of an
individual or even a mean for
individuals’’ but is a level of
nutrient intake that should be
adequate for most individuals.
EAR is the level of nutrient
intake adequate for half of
the individuals in a
population.
Phillips, S.M, et al. Int J Sport
Nutr Exerc Metab 2007, 17
Suppl, S58-76.
Higher Needs
Repair
Immunity
Lean Mass
Witard OC, et al. Int J Sport
Nutr Exerc Metab 2019; 29:
165-174.
Protein needs of athletes

Tarnopolsky, 2010, In Burke and Deakin, Clinical Sports Nutrition
Do athletes need more protein?

Protein requirement: more than daily
amount
– Is it too simplistic to rely on recommendations of a particular
amount of protein per day?
– Must take into account demands of the individual goals and
training regimen of each athlete
• Requirements range: 1.2-2.0g/kg/d
• Regular spread of high quality protein – ingest daily targets as
0.3g/kg after key sessions and meals
• 15–25g protein across the typical range of athlete body sizes;
~10g EAA
• Flexible, adjustment for periodisation of training and competition
(Thomas, D.T., et al. Med Sci Sports Exerc 2016, 48, 543-568)

Protein requirement: more than daily
amount
– Other factors are likely far more important than
quantity
– Timing in relation to exercise/other nutrients (carbs)
– Distribution throughout the day
– Dose
– Type of protein – quality
– Total energy intake
(see Moore et al. In Burke and Deakin, Clinical Sports Nutrition (5th edition). McGraw-Hill Pty Ltd, North Ryde, pp.94-113.)
Free pickit image

End Part 1

Part 2: Protein metabolism during exercise

Protein function
– Structural and regulatory functions
– Skeletal muscle proteins include:
– Contractile myofibrillar proteins (e.g. actin and myosin) essential
for muscular contractions (skeletal and heart)
– Structural proteins (e.g. collagen)- provide physical scaffolding
for muscle cells to transfer forces to bone levers
– Energetic mitochondrial proteins - generate the ATP energy
necessary for essentially all cellular function
– Regulatory enzymes - catalyse metabolism of many chemical
reactions for cellular functions (e.g. ATP hydrolysis and synthesis)
– Haematological proteins – oxygen delivery and plasma volume
(e.g. red blood cells)
Moore, D, Phillips, S, Slater, G. Protein. In Burke and Deakin, Clinical Sports Nutrition (5th edition). McGraw-Hill Pty
Ltd, North Ryde, 2015 pp.94-113.
Moore, D, Burd,N, Slater, G. Protein needs for the athlete. In Burke and Deakin, Clinical Sports Nutrition (6th
edition). McGraw-Hill Pty Ltd, North Ryde, 2021 pp.67-85.
This Photo by Unknown Author is licensed under CC BY-SA.
https://upload.wikimedia.org/wikipedia/commons/thumb/9/90/Musc
ular_system-back.svg/1200px-Muscular_system-back.svg.png

Histidine (His)* Tyrosine (Tyr)
Valine (Val) Glycine (Gly)
Leucine (Leu) Alanine (Ala)
Isoleucine (Ile) Cysteine (Cys)
Lysine (Lys) Serine (Ser)
Methionine (Met) Aspartate (Asp)
Threonine (Thr) Asparagine (Asn)
Phenylalanine (Phe) Glutamate (Glu)
Tryptophan (Trp) Glutamine (Gln)
Arginine (Arg)
Proline (Pro)
C C C C C C C C C
Amino acids
Essential
Non-Essential

Amino acids, peptides
and proteins
C
backbone
amine group acid group
side chain
NH2 COOH
C C C
valine leucine tyrosine
Peptide bond
Different amino acids
join together to form
proteins

Amino Acids are Recycled
Modified slide by Clare Woods, downloaded from sportsdietitians.com.au
Meat,
poultry,
seafood,
eggs, milk,
cheese,
yoghurt,
nuts, seeds,
legumes,
grains
(fruit & veg
minimal)
Daily
turnover,
↑ exercise
Mainly urea
Fuel
C- skeletons
https://thumbs.dreamstime.com/m/strong-arm-icon-muscle-
clipart-illustration-33142780.jpg

How do we measure protein needs?
Measure diet
protein
Protein ~16% N
N (g) = Protein
6.26
Measured
Better
methods
now use
tracers,
muscle
biopsy
Free pickit image

Protein use during exercise
 Branched chain AA (BCAA) preferentially oxidised
 BCAA = isoleucine, leucine and valine
 Glutamate dehydrogenase oxidises BCAA
 Rest 5-8% activity vs 20-25% during exercise
 Decreased activity good for positive N balance
Free pickit image

Regulation of glutamate dehydrogenase
– Activation ↑ by:
– ↓ [ATP/ADP]; ↓ [muscle glycogen]
– CHO limiting → use amino acids
– Endurance exercise
– Activation ↓ by:
– CHO loading or ingestion during exercise
– Preserves muscle protein
Counterproductive to
oxidise proteins since they
serve either a structural or
functional role
http://scoprilamela.it/wp-content/uploads/2015/07/PowerIcon.png

How much protein is used in endurance exercise?
 Most energy comes from CHO and lipid oxidation
 ~2-6% energy from AA during endurance exercise (Tarnapolsky, et al,
Nutr. 2004; 20: 662-668)
 Higher [urea] in urine and sweat post exercise
 AA oxidation is ↑ by
 > duration/intensity (Lamont et al. MSSE, 2001; 33: 237-241)
 ↓ muscle glycogen (Howarth et al, J Appl Physiol, 2010, 109: 431-438)
 ↑ protein diet (Bowtell, et al. J Physiol, 1998; 85: 1744-52)
 being male (Phillips et al , Am J Physiol, 1997; 273: E99-E107)
Use tracers
Free pickit image
Moore, D, Phillips, S, Slater, G. Protein. In Burke and Deakin, Clinical
Sports Nutrition (5th edition). McGraw-Hill Pty Ltd, North Ryde, 2015 pp.94-
113.

Endurance exercise & protein metabolism
Does endurance training promote protein sparing?
 Sedentary → endurance trained 38 d
 Leucine oxidation & glutamate dehydrogenase
activity lower after endurance training
 Supports ‘protein sparing’ with endurance training
McKenzie et al. Am J Physiol Endocrinol Metab, 2000; 278: E580-E587.
 Endurance training ↓leucine oxidation
 Probably due to enhanced lipid use & glycogen
sparing
 Protein requirements for endurance athletes?

Phillips Nutrition 2004
Balance fluctuates
with feeding over
the day
Further stimulated
by Resistance
Training
Protein balance & resistance exercise

Protein Metabolism & Resistance Exercise
Biolo et al Am J Physiol 1995, 1997 (in Phillips
Nutr 2004)
Fasted
rest
Fed
rest
Fasted
RT
Fed
RT
BEST = FED + RT
*Protein synthesis ↑
up to 48 hrs post a
single bout

Novice vs trained
Tony Pearson
Untrained bigger synthesis and
breakdown with training. Need
MORE protein than well trained.
↑0.25-0.5kg/week possible
but depends on genetics and
training history
http://meganandtimmy.com/2012/07/02/273365-
like-the-sands-in-an-hour-glass/weakling/
https://en.wikipedia.org/wiki/Tony_Pearson_(bodybuilder)
Phillips et al Am J Physiol 1999; E118-E124

End Part 2

Part 3: Protein intake – timing, type, (amount), and
other factors

Timing of intake: before/during
– Before exercise
– No clear advantage
– If a short bout, pre-feeding may provide amino acid source for protein
remodelling post-exercise
– During exercise
– Aerobic/endurance exercise*
• If >1.5 hours or multiple bouts, intake may → ↓ endogenous protein
use for fuel
• Protein ingested following exercise could then be more available for
muscle protein synthesis
– Resistance exercise**
• For sessions >2 hours with breaks, could be beneficial
• Uncertain value for shorter sessions
This Photo by Unknown Author is licensed under CC BY-SAhttps://3.bp.blogspot.com/-r6uB43DtTYc/V-f4FNRMRrI/AAAAAAAACrY/B4Vgkd-
tqwMYsC4kFGzJdt4k2yIf1HsAACLcB/w1200-h630-p-k-no-nu/protein%2B%25282%2529.jpg
*[Koopman et al (2004), Beelan et al (2011) in,,,,], **[Beelen et al, 2008) in…]
Moore, D, Phillips, S, Slater, G. Protein. In Burke and Deakin, Clinical Sports Nutrition (5th edition). McGraw-Hill Pty Ltd, North Ryde, 2015 pp.94-113.
Moore, D, Burd,N, Slater, G. Protein needs for the athlete. In Burke and Deakin, Clinical Sports Nutrition (6th edition). McGraw-Hill Pty Ltd, North Ryde,
2021 pp.67-85.

Timing of intake: following
– Protein ingestion → ↑ MPS post exercise
– Critical to recovery
– Consumption up to 24 hours contributes to
enhanced remodelling
– 0-2 hours still in guidelines (Thomas, D.T., et al. Med
Sci Sports Exerc 2016, 48, 543-568)
Moore, D, Phillips, S, Slater, G. Protein. In Burke and
Deakin, Clinical Sports Nutrition (5th edition). McGraw-
Hill Pty Ltd, North Ryde, 2015 pp.94-113.

Timing of intake: following
Schoenfeld BJ, Aragon AA, Krieger JW. The effect of
protein timing on muscle strength and hypertrophy: a
meta-analysis. J Int Soc Sports Nutr. 2013; 10: 53.
DOI: doi.org/10.1186/1550-2783-10-53.
– Protein ingestion → ↑ MPS post exercise
– Critical to recovery
– Consumption up to 24 hours contributes to
enhanced remodelling
– 0-2 hours still in guidelines (Thomas, D.T., et al. Med
Sci Sports Exerc 2016, 48, 543-568)
Moore, D, Phillips, S, Slater, G. Protein. In Burke and
Deakin, Clinical Sports Nutrition (5th edition). McGraw-
Hill Pty Ltd, North Ryde, 2015 pp.94-113.
Figure1: impact of protein timing on strength by study
Figure 2: impact of protein timing on hypertrophy by study

Optimal amount?
Moore et al Am J Clin Nutr 2009
Ceiling effect at 20 g
protein ~ 10 g EAA

Bolus, Intermediate or Pulse?
Bolus: 2 x 40 g protein (6 hly)
Intermediate: 4 x 20 g (3hly)
Pulse: 8 x 10 g (1.5 hrly)
Intermediate best
http://liftandfuel.com/4-easy-to-prepare-high-protein-food-options/.
Areta et al J Physiol, 2013; 591: 2319-2331

Pre-sleep protein ingestion?
Snijders T, Trommelen J, Kouw IWK, Holwerda AM, Verdijk LB, van Loon LJC. The Impact of Pre-sleep Protein Ingestion on the Skeletal Muscle
Adaptive Response to Exercise in Humans: An Update. Frontiers in nutrition. 2019;6:1-8.

Pre-sleep protein ingestion?
Snijders T, Trommelen J, Kouw IWK, Holwerda AM,
Verdijk LB, van Loon LJC. The Impact of Pre-sleep Protein
Ingestion on the Skeletal Muscle Adaptive Response to
Exercise in Humans: An Update. Frontiers in nutrition.
2019;6:1-8.

Is WHEY the way?
Hartman et al Am J Clin Nutr 2007
Cribb & Hayes Int J Sports Nutr Exerc Metab 2006
Milk
20% whey; 80% casein
Whey a soluble and ‘fast’ protein
Dr Oliver Witard on source: https://www.youtube.com/watch?v=wny8smtLB1Y
(Fat and bone-free
mass)

Why does WHEY work so well?
– Whey: highest BCAAs of any protein.
– The key could be the BCAA leucine.
– After exercise, leucine stimulates
signaling pathways
– Stimulates muscle protein synthesis
– ‘‘leucine trigger’’
From: Phillips, SM, Sports Nutrition Conference Proceedings, Canberra 2010
Hawley, J.A.. Appl Physiol, Nutr, Metab
2009, 34, 355-361.

Muscle hypertrophy: energy and macronutrients
– Energy surplus
– estimate: 1500-2000kJ/day
– Protein
– greatest gains associated with
1.6g/kg/d (Morton et al BJSM 2018:; 52:
376-384)
– Carb
– primary substrate used for
resistance training
Slater GJ, et al. Is an Energy Surplus Required to Maximize Skeletal
Muscle Hypertrophy Associated With Resistance Training. Front Nutr.
2019; 6: 131. DOI: doi.org/10.3389/fnut.2019.00131.

Hormones: testosterone
– Illegal WADA
– Evidence of ↑ lean mass from
• male female differences
• Pharmacological doses
– Can ↑ lean mass without training
– Effects magnified with resistance training
– ↑ protein synthesis & intracellular AA re-utilisation
– Does not affect protein degradation
– Acute resistance exercise ↑ plasma [testosterone]
https://www.drugwatch.com/testosterone/supplements/
(see Tarnapolsky. In Burke and Deakin, Clinical Sports Nutrition (4th edition). McGraw-Hill Pty Ltd, North Ryde, pp.61-95.)

Hormones: insulin
– Net stimulatory effect on protein synthesis
– Usually causes ↓ in degradation
– AA + insulin stimulates protein synthesis
– Provide basis for Protein + CHO in the early post-exercise
period
https://thumbs.dreamstime.com/m/strong-arm-icon-muscle-clipart-illustration-33142780.jpg

End Part 3

Part 4: High and low protein intakes, energy
restriction, older athletes bed rest and injury

Risks of excessive protein intake
– What is high?
– Athletes typically consume 1.4-1.9g/kg, higher intakes appear
safe, but more research needed on upper bound
– Doesn’t appear to impact hydration, bone health, or kidney
function (in healthy people)
– May displace other nutrients
– Possible contamination issue
– Waste money
(see Moore et al. In Burke and Deakin, Clinical
Sports Nutrition (5th edition). McGraw-Hill Pty
Ltd, North Ryde, pp.94-113.)

Athletes at risk of low protein intake
– ‘Making weight’ sports
– Sports where leanness is prized
• e.g gymnastics, dance, diving
– Eating disorders
– Extreme diets/extreme vegetarianism
Free pickit image

Older athletes
– Protein requirements may increase with age
– May need ≥ 1.2g/kg (Bauer, J et al. J Am Med Dir Assoc 2016; 14: 542-559)
– 35-40g leucine-rich protein > muscle-damaging exercise
(Doering, T.M. et al. Int. J. Sport Nutr. Exerc. Metab. 2016, 26, 168-178).
– Lower for those with impaired kidney function (e.g.
sometimes in T2D)
– Attention to timing, distribution, quality of protein same as
for younger athletes
see Gifford, JA and O’Connor, HT, in Belski, R, Forsyth, A,
Mantzioris, E (eds) Nutrition for Sport, Exercise and Performance.
Crows Nest: Allen & Unwin, in press.
https://3.bp.blogspot.com/-
WQIxG1tYlg0/Ws4Gasc04pI/AAAAAAAATQU
/Q4GyLWilXw0xpQcyRCjJYQ98ag51oZXWgCLcBGAs/s1600/ab0
d7209d2239b62c2d2cecc83b0d800.jpg

Negative energy balance
– Muscle protein turnover may ↓ during energy restriction
– Resistance training may assist maintenance of muscle mass
and performance during negative energy balance
– A slightly greater meal protein intake (0.3-0.4 g/kg) and
↑ daily protein intake may
– enhance protein synthesis
– ↑ meal satiety
(see Moore et al. In Burke and Deakin, Clinical Sports
Nutrition (5th edition). McGraw-Hill Pty Ltd, North Ryde,
pp.94-113.)
Free Pickit image
Longland TM, et al. Higher compared with lower dietary protein during
an energy deficit combined with intense exercise promotes greater lean
mass gain and fat mass loss: a randomized trial. Am J Clin Nutr.
2016;103(3):738-46.

Injury/bed rest
– 10x 23yo males 7d bed rest*→
– ↓1.4 ±0.2kg lean tissue (P<0.01)
– 3.2 ±0.9% ↓ quadriceps cross sectional area (P<0.01)
– 6.9 ±1.4% ↓ one rep max (P<0.01)
– 29 ±5% ↓ whole body insulin sensitivity (P<0.01)
– Physical activity may be restricted with long periods of bed
rest → ↓ muscle protein synthesis**
– In patients who cannot move, neuromuscular electrical
stimulation along with pre-sleep protein ingestion → ↑ MPS***
*Dirks ML, Wall BT, van de Valk B, Holloway TM, Holloway GP, Chabowski A, Goossens GH, van Loon LJ. One Week of Bed Rest Leads
to Substantial Muscle Atrophy and Induces Whole-Body Insulin Resistance in the Absence of Skeletal Muscle Lipid Accumulation.
Diabetes. 2016;65(10):2862-75.
**Wall BT, Dirks ML, van Loon LJ. Skeletal muscle atrophy during short-term disuse: implications for age-related sarcopenia. Ageing Res
Rev. 2013;12(4):898-906.
***Wall BT, Dirks ML, Verdijk LB, Snijders T, Hansen D, Vranckx P, Burd NA, Dendale P, van Loon LJ. Neuromuscular electrical stimulation
increases muscle protein synthesis in elderly type 2 diabetic men. Am J Physiol Endocrinol Metab. 2012;303(5):E614-23.
No attribution

End Part 4

Part 5: Practical Aspects

Guidelines
– Thomas, DT, et al. Nutrition and Athletic Performance. J Acad Nutr Diet
2016, 116, 501-528; DOI: 10.1016/j.jand.2015.12.006.
– Suggest: International Journal of Sports Nutrition and Exercise
Metabolism 2019 vol 29 issue 2: IAAF Consensus Statement: Nutrition
for Athletes.
This Photo by Unknown Author is licensed under CC BY-NC. http://1.bp.blogspot.com/-
RgvlqM7f9Q8/VcurgxmErWI/AAAAAAAAEPg/FlNozSsLq0Y/s1600/Screen%2BShot%2B2015-08-
12%2Bat%2B3.23.51%2BPM.png

Protein requirements – practice tips
– It is essential to meet the increased protein needs of strength and
endurance athletes in hard training to optimise adaptation and
recovery.
– Recommended protein intakes for strength-trained athletes usually
range from ~ 1.2 to 1.7 g/kg/d but adequacy of total intake is
simplistic
– Early phase of strength training when the most significant gains in
muscle size occurs and protein needs are greatest
– Protein requirements are lower for trained
– more efficient protein use
– Higher intake are a waste!
– Timing, dose, distribution, quality, energy intake (and digestion rate)
more important than total intake
– ~10gEAA (15-25g protein; no more than 40g; 0.3g/kg key sessions and
meals)
– 0-2hours post-exercise
• Moore et al. In Burke and Deakin, Clinical Sports Nutrition (5th edition). McGraw-Hill Pty Ltd, North Ryde, pp.94-113.
• Thomas, D.T., et al. Med Sci Sports Exerc 2016, 48, 543-568
Free Pickit image

Do athletes eat enough protein?
Phillips, SM. Nutrition 2004; 20: 689-695
RDI
What athletes
consume

Food sources

Milk vs Protein Powder
Skim Milk Skim Milk Powder Protein Powder
100mL 100g 30g 100g 30g
Energy (kJ) 152 1519 455.7 1680 504
Total Fat (g) 0 0.8 0.24 7.3 2.19
Saturated Fat (g) 0 0.51 0.153 4.6 1.38
Carbohydrate (g) 5.5 56 16.8 15.3 4.59
Sugars (g) 5.5 56 16.8 14.4 4.32
Dietary Fibre (g) 0 0 0 1.3 0.39
Protein (g) 3.7 34.9 10.47 66.6 19.98
Calcium (mg) 120 1100 330
Sodium (mg) 40 420 126 164 49.2
Potassium (mg) 166 1800 540
$ 0.125 0.57 0.171 $6.67 $2.00
$1.25/L Coles
brand
$5.70/kg Coles
Brand
"High Protein"
$25/375g
(popular brand from
Coles)

Protein Timing

Applications:
Middle and long
distance running
Burke L (2007) Practical Sports Nutrition. Human
Kinetics, Champaign.

Applications:
Middle and long
distance running
Burke L (2007) Practical Sports
Nutrition. Human Kinetics, Champaign.

Applications:
Swimming and
rowing
Burke L (2007) Practical Sports Nutrition. Human
Kinetics, Champaign.

Applications: Swimming and rowing
Burke L (2007) Practical Sports Nutrition. Human Kinetics, Champaign.

End Part 5

End
Thank you


Lecture Objectives
– How many amino acids are required for protein synthesis and how many
are essential for adults?
– Which are the branched chain amino acids?
– Under what conditions would you expect protein/amino acids to provide
more fuel during exercise?
– Understand the effects of endurance and resistance training on protein
metabolism
– Describe the protein requirements of athletes and sedentary individuals
– Describe and explain the interplay between carbohydrate, protein and
energy intake for lean mass gain
– Explain the recent research regarding the potential ‘protein window’ pre
and post exercise.
– Outline recommended strategies for assisting athletes to gain lean body
mass

Lecture Objectives
– Outline the potential problems or risks of excessive protein intake
– Outline which athlete groups may be more at risk of inadequate
protein intake
– Know major sources of protein in the diet
– Understand (generally) how nitrogen balance is measured and
calculated
– What is the recommended protein intake for endurance and
resistance trained athletes?
– Understand the changes in protein requirements for novice compared
to well trained endurance and resistance trained athletes
– Understand the effect of anabolic steroids on lean mass gain
– Understand differences between whey and casein proteins in milk
with respect to insulin and promoting lean mass gain

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