Transcript Protein

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 nonessential (12)
Amino acids
• Non-essential
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Alanine
Arginine (ess in children)
Asparagine
Aspartate
Cysteine
Glutamate
Glutamine (ess in children)
Glycine
Proline
Serine
Tyrosine
Histidine (ess in infants)
• Essential
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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
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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): 4954, 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
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Protein intake during exercise
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Suggested small amnt protein in sports drink can improve endurance capacity (Ivy et al.,
2003; Saunders et al., 2004)
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However rate CHO delivery was less than optimal – 37 – 47 g CHO/hr
Drinks not matched for caloric content
Van Essen et al., (2006)
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Sports drink  60g CHO/hr
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80km tt – no difference – but both better than placebo
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Romano-Ely et al., (2006) – no difference when matched for caloric content
Saunders et al., (2006) 60g CHO/hr, + prot.
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Increased oxidation – spare muscle glycogen etc;
increased TCA intermediates;
central fatigue
fuel transport across intestine,
increased insulin
Muscle recovery?
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Saw improvement in late race time-trial performance
Mechanism?
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6% CHO, 6%CHO +2% whey, sweetened placebo
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 postexercise 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