24. Nutritional interventions

Question 1

What does sports nutrition (& training) aim to do?

Answer 1

1. optimise body substrate stores before exercise/competition
2. enhance substrate availability during exercise and spare muscle glycogen stores & optimise performance
3. increate rate of glycogen synthesis in recovery phase
4. increase muscle protein synthesis & muscle repair
5. reduce muscle damage

Question 2

Effect of resistance exercise on protein metabolism

Answer 2

Need food intake to be in a positive protein balance

Question 3

CHO ingestion and protein metabolism

Answer 3

CHO intake does not affect protein synthesis and does not result in a positive protein balance

Question 4

CHO effects via insulin

Answer 4

PI-3 kinase/mTOR pathway

• Insulin binds to receptor which P’lates IRS-1
• increase in Akt P’lation
• GLUT4 translocates to membrane
• increased glucose uptake

**but not sure how this affects protein synthesis

POSSIBLE THAT INSULIN MORE IMPORTANT IN REGULATING MPB THAN MPS!!

Question 5

Protein intake and MPS

Answer 5

Protein intake stimulates protein synthesis

Question 6

AA intake and MPS

Answer 6

Intake of essential AA stimulates protein synthesis.

*in study, ingestion of drink CHO + EAA has effect on mTOR pathway, phosphorylates 4OBP1, therefore protein synthesis is started/increased

Question 7

How do essential AAs stimulate protein synthesis?

Answer 7

Via increased signalling through mTORC1

Question 8

How much protein do you need?

Dose-response curve EAA-FSR; young vs elderly

Answer 8

~25g protein/meal enough to maximally stimulate MPS

Within 10g of essential amino acids, there is increased in both young & elderly participants

Begins to plateau after 10g EAA

Difference b/w young & elderly can be attributed to:

• anabolic resistance in elderly
• smaller increase sufficient for elderly participants

Question 9

Does continuous AA feeding further increase MPS?

Answer 9

AA infusion rapidly increases MPS, h/e stimulatory effect of increased AA availability on protein synthesis is relatively short.

Question 10

What is in milk?

Answer 10

4% fat
5% CHO (lactose)

3% protein, ~30g/L
80% of this protein is casein (slow releasing protein)
20% whey (smaller peptide chains)

Question 11

Whey vs. casein

Answer 11

Whey is more rapidly digested than casein and may be more effective to increase MPS.

Leucine is more abundant in whey compared to casein and casein hydrosylate.

Increase in Leu matches up nicely with increase in MPS in whey vs casein.

Question 12

Is a rapidly digested protein more efficient in stimulating protein synthesis compared to casein?

Answer 12

AA derived from dietary protein hydrosylate appear quicker in circulation, resulting in higher protein synthesis.

33% increase

Question 13

What is so special about leucine?

Answer 13

• stimulates MPS
• inhibits proteolysis
• administration inhibits protein breakdown
• stimulates protein synthesis
• only AA that has significant effect on mTOR signalling
• Leucine content in meal affects anabolic response

Question 14

Leucine and mTOR signalling

Answer 14

Leucine stimulates mTORC1 and is very important for maintaining the building of polypeptides.

Leucyl-tRNA synthetase (LARS) recognises how much Leu is present in system and attaches it to tRNA.

LARS then transports leucyl-tRNA combination to ribosome & attaches it to polypeptide.

Question 15

What does the RDI tell us is the daily protein intake for sedentary individuals?

Answer 15

Minimally require 0.75-0.80g/kg for 98% of the population.

• not an optimal intake
• strenuous exercise may increase protein needs

Question 16

What is the RDI (protein) for athletes?

Answer 16

Recommended intake of 1.2-1.7g/kg/day of protein for athletes.

Question 17

What is the relatively normal diet of an active 25-30yo male of 80kg body weight?

Answer 17

Energy intake = ~3000 kcal/day (~13MJ/day)

Macronutrient ratio

• CHO 50%,
• fat 35%
• protein 15%

Daily protein intake:
112g protein/day, corresponding to 1.4g/kg/day

Question 18

Post-exercise protein intake from milk vs soy milk.

Answer 18

Chronic post-ex consumption of milk promotes greater hypertrophy during the early stages of resistance training in novice weightlifters when compared with isoenergetic soy or CHO consumption.

Question 19

During weight loss, how do you reduce loss of muscle mass?

Answer 19

Increased protein uptake, particularly during breakfast.

Question 20

When is the best time to increase protein intake?

Answer 20

Breakfast is low in protein & represents the biggest opportunity to increase protein intake in frail elderly.

Question 21

Long term Leu supplementation & exercise in the elderly

Answer 21

12 week supplementation with Leu did not increase muscle mass & strength

12 week supplementation with protein during post-exercise recovery did not further increasing muscle mass and strength.

Question 22

What are the effects of Citrulline on muscle?

Answer 22

With 2% horse serum withdrawal, citrulline completely prevented serum withdrawal-induced muscle wasting whereas R and L did not.

Citrullin does not exert its effect via mTOR.

Question 23

Is glycine an effective anti-inflammatory agent? How (or where) are we testing potential of G?

Answer 23

Yes, when used with LPS (induces sepsis), there is preservation of myotube diameter.

Testing potential of glycine supplementation in animal models of sepsis and cancer cachexia.

Question 24

Effects of G supplementation with cancer?

Answer 24

Reduces tumour growth and muscle loss (compared with alanine and citrulline).

Reduces Atrogin-1 mRNA expression and helps maintain the protein synthetic machinery.