Protein 1

Question 1

How can the 20 amino acids be categorised?

Answer 1

8 essential: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

8 oxidised as fuel: alanine, asparagine, aspartate, glutamate, isoleucine, leucine, lysine, valine

Isoleucine, leucine, valine taste horrible so are put into protein substitutes so that the product can claim that BCAA are contained
- Essential cannot be produced by the body - must be consumed
- Other 12 can be made from the essential amino acids

Question 2

Describe the general structure of an amino acid:

Answer 2

• Alpha carbon in middle
  
  • Hydrogen and amino side groups
  • Amine and carboxyl groups
  • R side chain

Question 3

How much FAA can be absorbed by the gut and liver?

Answer 3

Peptide fragments and free amino acids are absorbed almost exclusively in the small intestine
- Gut extracts 40-50% of available amino acids
- Remaining 50% are taken up by the liver

Question 4

Define:
NPB
MPS
MPB
Describe protein turnover

At what ages are there significant changes in protein

Answer 4

• NPB = MPS – MPB
• NPB: Net muscle protein balance, what we lose is balanced against what we gain
• MPS: Muscle protein synthesis
• MPB: Muscle protein breakdown
• In sedentary individuals skeletal muscle mass essentially stable
• Always a state of dynamic equilibrium
• Dispensable AA can be put into FAA pool- continual turnover
• 18/20(major growth) to 50(protein degradation) - either side of these age ranges there are big protein changes occurring

Question 5

What are the sedentary protein requirements?

How can a person’s protein intake be measured?

Answer 5

• Sedentary requirements:
  
  • ~0.8 g/ kg/ day
• Measured by
  
  • Nitrogen balance techniques - simple measure of whole protein balance, measure all roots of loss and intake
  • Tracers techniques - measures MPS & MPB, looks at individual muscles
  • Dietary protein intake positively impacts NPB by regulating balance between MPS and MPB

Question 6

How does resistance exercise impact MPS and MPB?

Answer 6

• Postabsorptive state, an acute bout of resistance exercise stimulates MPS by more than 100% above basal levels - but NPB remains negative due to its association with MPB
  Synthesis responds more to feeding than breakdown
• Refractory period allows subsequent increase, if not then more protein will be excreted
• MPS response is amplified for approx. 24hrs, more for untrained individuals
• Protein on its own will not lead to lead mass gain, exercise is the stimulus and nutrition helps to support that stimulus adapt to the exercise

Question 7

How does resistance exercise impact NPB?

Answer 7

• Resistance exercise followed by MPS and MPB measures at 3h, 24h and 48h
• protein type, age, and potentially the gut microbiota interact to influence amino acid partitioning and specifically how these factors change in the context of resistance exercise
• exercise sensitizes the muscle to hyperaminoacidemia
• Exercise increase protein breakdown - induces a less negative effect on protein balance for up to 2 days on untrained people, but nutrition is needed to make it positive

Question 8

Is timing of protein intake important?

Answer 8

• Amino acid-carbohydrate mixture given 1 h or 3 h post-exercise
• No difference in MPS between feeding 1 h and 3 h post-exercise
• No anabolic window, but there is a time period which can maximise response(after 1 hr, after 3hrs) - there is a window of opportunity

Question 9

What protein intake provides maximal MPS?

Answer 9

20 g protein every 3 h maximised MPS compared to 10 g every 1.5 h or 40 g every 6 h - what the general person does daily

Question 10

What are some factors which need to be considered when deciding the amount of protein intake?

Answer 10

• No effect of body size
• Body size needs to be considered as it may influence the amount of protein they need to eat
• More protein may be needed for more full body sports, more energy expended
  Amino acid intake at sufficiently high levels (~70 g) also appears to inhibit proteolysis in an insulin-independent manner
  continuing to ingest amino acids beyond the point at which MPS is maximally stimulated (i.e., 20–30 g in healthy young adults), intracellular amino acid concentrations rise and inhibit MPB rather than further stimulating MPS and, by extension, promotes a greater NPB.

Question 11

Is there any difference in MPS between sexes?

Answer 11

• Lower body resistance exercise followed by 25 g whey protein in 10 young men/ women
• No sex difference in MPS
• Protein differences are almost identical

Question 12

How can different sources of protein impact MPS?

Answer 12

• Milk (animal protein) increases MPS more than the same amount of soy (plant protein)
  
  • Likely due to differences in amino acid composition in protein sources
• Whey, casein or soy protein, each providing 10 g EAA (~22 g protein) - suppressed hunger, better than whey protein, hence stimulating a more pronounced secretion of GLP-1(satiety-inducing hormone)
• Casein is 80%, whey is 20-25% of protein in milk
• demonstrated greater plasma elevations of cholecystokinin (CCK), another satiety-inducing hormone secreted by the gut, after whey protein consumption
• Post-prandial MPS: whey > soy > casein when consumed post-exercise

Question 13

Describe why athletes would co-ingest CHO and protein?

Answer 13

• 25g whey protein or 25g whey + 50g maltodextrin(raises insulin)
• No effect of CHO on MPS
• could be helpful for endurance athletes to maintain energy stores

Question 14

Explain overnight recovery of MPS

Answer 14

• Evening exercise followed by post-exercise recovery drink and pre-bed recovery drink containing 0 g or 40 g casein protein
• Protein taken from cows(milk), casein is more available than whey
• Pre-bed protein increased overnight MPS - amplified

Question 15

What are the recommendations to maximise NPB?

Answer 15

1. Exercise is vital
2. Consume sufficient energy
3. Consume sufficient high quality protein
4. Consume at least 20-25 g every ~3-4 h
   
   • > 0.3 g/ kg
5. Consume a serving of protein before bed
   
   • ~30-40 g
     Plan protein intake for breakfast