Protein and amino acids

Proteins

• Contain C, H, O, N and some have S, Fe, P, Co

• Long chains of amino acids

• 20 amino acids• Fairly water sol• Essential and non-

essential (12)

Amino acids

• Non-essential– Alanine– Arginine (ess in children)– Asparagine– Aspartate– Cysteine– Glutamate– Glutamine (ess in children)– Glycine– Proline– Serine– Tyrosine– Histidine (ess in infants)

• Essential– Isoleucine– Leucine– Lysine– Methionine– Phenylalanine– Threonine– Tryptophan– Valine

Peptide bonds

• 2 amino acids linked by dehydration

• Results in covalent bond between amino gp and carboxylic gp

• Results in peptides• (Dipeptides -

polypeptides)• Negatively charged in

solution

7 essential functions

• Support

• Movement

• Transport

• Buffering

• Metabolic regulation

• Coordination & control

• Defense

Amino acid metabolism

Protein Intake

• Not associated with Western diseases of affluence

• Protein deficiency uncommon in developed world

• RDA varies ~0.8 g/kg bw• Intake usually ~80-100g/day, 10 – 15%

total energy intake• Sources – meat/fish – complete protein• Grains, legumes - incomplete

Sources of protein in the British Diet.

>60% from animal products

How is protein metabolism studied?

• Eg.– Urea concentration in urine and sweat;– N balance = Nt – Nu – Nf – Ns = 0

• +ve N balance – in children, pregnancy, during resistance training

• -ve N balance– Lack of other energy nutrients (Butterfield, 1987); DM; fever,

burns, dieting/starvation

– Isotopes – radiolabeled or stable (3H, or 13C)– Tracer incorporation/release into/from a specific

protein– Leucine oxidation

N-balance• Protein breakdown generally

increases modestly with exercise;

• Protein synthesis rises substantially following endurance and resistance exercise

idea that protein intake might be higher in sport– Due to increased breakdown

during training;– Due to increased synthesis in

recovery period – eg. new myofibrils or mitochondria

• Is N-balance relevant to athletes? Muscle size, strength, oxidative capacity

Net Protein Balance (NPB)

• Rest/fasted state– NPB –ve (ie. B’down > synth)

• After exercise in fasted state– Both synth and b’down ↑, NPB still –ve but less so

than rest as ↑ synth> ↑ b’down

• Eating CHO/αα before/immediately post ex– ↑ αα availability & transport into cell, counteracts

catabolic state & ↑protein synth– ↓b’down– +ve NPB

Contribution to energy

• At rest contributes between 5 – 15%– Decreases in exercise due to CHO and fat– Prolonged endurance may contribute up to 10% - via alanine –

glucose cycle.• Controversy – 2 camps

– Those who believe sport ↑ protein req• Lemon et al., Tarnopolsky et al.

– Those who believe req are not different to sedentary people – increased efficiency use of αα

• Butterfield et al.,

• Evidence for both – practically not often an issue– Few studies on protein intake and performance– Meta-analysis – protein supplements no impact on muscle

mass (Nissen and Sharp, 2003)

Protein and resistance• Suggested increased requirements are related to

requirement for muscle hypertrophy• After resistance exercise muscle protein turnover is

increased due to increase in synthesis and breakdown (breakdown to a lesser degree)

• Increased protein requirements are controversial– many short studies– when start training see –ve N balance– but reversed within 12 days of training

• Recommendation is 1.6 – 1.7 g/kg bw, acceptable range 20 – 40% (max)– Again often met by a normal diet.

• Tarnopolsky et al. (1992) found intake of 2.4g/kg/d was no more effective than 1.4g/kg/d in permitting strength and weight gain

Protein and resistance – amino acid supplements

• Amino acid supplements touted as way of increasing GH, insulin anabolism – but no evidence to support if protein consumption > 2g/kg/d.

• Supplements of individual amino acids popular in certain circles in attempt to stimulate release of growth hormone and insulin eg. Arginine– High doses of arginine, ornithine and lysine may increased

levels of GH and insulin but no effect on LBM or muscle function (Merimee et al., 1969)

• However studies showing hormonal effect used 30g amino acids, cf. 1-2g/day in typical supplements – which have failed to show an effect

• Effect due to large doses still < effect of 60min moderate exercise

Protein and resistance – CHO and/or energy

• CHO and protein taken together (ie. As in balanced diet) hormonal state favouring net protein synthesis (Rasmussen et al., 2000)– Carbohydrate inhibit muscle protein breakdown, but not stimulate

synthesis– Also restores glycogen stores.

• Testosterone secretion is optimal when protein:CHO ratio is 1:4 (ie. 15%:60% as in balanced diet) Volek et al., (1997)

• If an overall energy deficit exists (due to heavy training/dieting) then –ve N balance will occur even if protein intake is 2x RDA.

• Gater et al., (1992)– Resistance training for 10 weeks on one of 3 diets

• No additions to normal diet• Amino acid supplement• +ve energy balance

– Greatest gains in lbm with +ve energy balance

Volek, et al.,Testosterone and cortisol in relationship to dietary nutrients and resistance exercise. J. Appl. Physiol. 82(1): 49-54, 1997.

i.e. “balanced diet” optimal for maintenance of teatosterone levels.

Source of protein

• Which protein or amino acid most effective at post-exercise anabolism?

• Tipton et al. (2004) no difference in NPB after post-ex ingestion of casein or whey

• Koopman et al., (2005) – no difference casein hydrolysate with or without leucine

• Wilkerson et al., (2006) milk protein > soy proteins

• Interaction with other nutrients ingested and timing in relation to exercise.

• More studies warranted.

Protein and resistance – why not consume loads of protein?

• Reduced CHO and fat intake – most imp.

• Amino acids may cause GI distress due to osmotic effect increased oxidation ie. Adapt and burn as metabolic

fuel.• Excretion of urea requires dilution with water and so may

contribute to dehydration• Excess protein catabolism results in urinary loss of Ca• Unknown whether ingestion of one effect on another

nutritional imbalance.• No negative effects on kidney function

Other factors

• Impossible to maintain +ve N balance when in energy deficit

• Complete vs. incomplete protein• Aa’s may be used preferentially by different

tissues• Other nutrients ingested

– Eg. CHO ↑ use of aa’s ingested concomitantly after resistance ex (insulin?)

• Timing – although dependent on type of protein• i.e. consideration of only amount of protein is

scratching the surface

At risk groups

• Those at risk of low energy (and thus low protein intake)– Amenorrheic female runners, male and female

gymnasts, female dancers– Weight class athletes/wt loss program– Training camp (sudden ↑ training)– Vegetarian athletes? – lower quality protein, lower

digestibility? – evidence lacking (Haub et al. 2002)• But possibly superior balance with reliance on animal protein

Protein and Endurance

• Exercise increases protein oxidation & N loss + synth mitochondrial enzymes

• Equivocal evidence over whether endurance athletes need more protein

• Training has protein sparing effect (McKenzie et al., 2000)

• Those that do advocate increased protein– 1.2 – 1.4g/kg bw– This is usually easily met due to the increase in food intake in

endurance athletes usually automatic increase in protein– Provided energy intake meets expenditure endurance athletes

probably do not need to supplement with protein.• Under nutritional (low energy or CHO) or metabolic

(intense training) stress can see increased oxidation• Studies consistently show higher oxidation in ♂

Protein and endurance• Protein intake during exercise

– Suggested small amnt protein in sports drink can improve endurance capacity (Ivy et al., 2003; Saunders et al., 2004)

• However rate CHO delivery was less than optimal – 37 – 47 g CHO/hr• Drinks not matched for caloric content

– Van Essen et al., (2006) • Sports drink 60g CHO/hr

– 6% CHO, 6%CHO +2% whey, sweetened placebo• 80km tt – no difference – but both better than placebo

– Romano-Ely et al., (2006) – no difference when matched for caloric content– Saunders et al., (2006) 60g CHO/hr, + prot.

• Saw improvement in late race time-trial performance– Mechanism?

• Increased oxidation – spare muscle glycogen etc;• increased TCA intermediates;• central fatigue• fuel transport across intestine,• increased insulin

– Muscle recovery?• Beneficial to protein balance, and attenuates post-exercise markers of muscle damage, and improves

subsequent exercise.– Saunders et al., (2007) – Coingestion of carbohydrate-protein during endurance exercise:

influence on performance and recovery IJSNEM 17: S87 – S103– Seifert et al., (2006) adding protein (1.5%) to CHO-containing drink (6%) improved fluid

retention

Protein and endurance

• Protein intake post exercise– Repair, synthesis muscle protein, synthesis muscle

glycogen– Levenhagen et al. (2002) – protein + CHO post-

exercise facilitates uptake of amino acids.– However feeding of CHO at frequent intervals

negates effects of additional protein (in terms of maximising glycogen stores – see CHO lecture) –only works when CHO intake is suboptimal

BCAAs

• Participate directly (fuel and prot synth), and indirectly (synth of neurotransmitters)– serotonin, dopamine and noradrenaline

• Often added to energy drinks to provide additional fuel

• However minor cf CHO and fat – and ingestion of CHO prevents increase in BCAA oxidation

• Supplementation unnecessary

Central Fatigue Hypothesis

• Proposed 1987 as fatigue mechanism (Newsholme et al.)

• In exercise FAs are mobilised and transported to muscles bound to albumin

• The amino acid tryptophan is also transported bound to albumin at the same binding site.

• Therefore as FAs increase in exercise, more tryptophan is released from albumin free tryptophan (fTRP)

Central Fatigue Hypothesis - theory

• BCAA and fTRP compete for carrier-mediated transport into the CNS – there TRP is converted to serotonin

• Increased ratio of serotonin:dopamine associated with tiredness

• In exercise muscle metabolism of BCAAs increases, decreasing plasma BCAA so transporters can carry more TRP to CNS

• Ingestion of BCAA raises fTRP:BCAA and therefore reduces transport of fTRP into CNS

Davis et al., (2000)

Central Fatigue Hypothesis - theory

• However studies ingesting TRP have not had any effects upon performance– Evidence in animals but not humans

• Some support for ingesting TYR (for DA) – in stress related environments (Owasoyo et al. 1992)

• Also lack of evidence for supplementing BCAAs – different in animals

• Evidence for exercise in heat – Mittleman et al., (1998)– But not supported by Watson et al. (2004) or

Cheuvront et al., (2004)

Conclusion

• Adequate energy is critical• If muscle hypertrophy is the primary goal then

hyperenergetic diet may be the most important recommendation– Suggested that 35 - 40% of total energy as protein

may be upper limit – any higher limits CHO and fat

• Evidence that protein intake above RDA may be beneficial to athletes – but– Little research into maximum tolerable protein intake;– Xs protein increases Ca loss– No evidence for kidney harm

Conclusion

• Recommendations of 1.2 – 1.8 g/kg/d are common

• Many high protein foods also high in fats (and food knowledge is not generally good in athletes)

• Most athletes already consume more than RDA in habitual diet

• Little evidence to support benefit of supplementation if eating a varied diet with complete/complementary protein

• No risk until >40% of energy intake

Calculation

• Protein intake to ↑ muscle protein by 5kg.yr-1 in 80kg athlete

• Muscle 75% water, 25% protein (i.e. 1.25kg ↑)• 1250/80kg/365d = 0.04g/kg/BM/d • 0.04 x 80kg = 3.2g protein/d ~100ml skim milk

(assumes all protein enters the muscle)• If assume only 25% enters the muscle• Then 400ml skim milk

Refs

• Tipton, K., and R. Wolfe (2004) Protein and amino acids for athletes. Journal Sports Sci. 22: 65-79

• Meeusen and Watson (2007) Amino acids and the brain: Do they play a role in ‘central fatigue’? Int J Sports Nutr Ex Metab 17

• IJSNEM Volume 17 - 2007