Protein

Question 1

What is the RDI for protein?

Answer 1

0.8-1.0g/kg/day

Question 2

What are the essential amino acids that must be supplied in food?

Answer 2

Histidine (in children)
Isoleucine
Leucine
Valine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan

Question 3

What are the 3 BCAA?

Answer 3

Isoleucine
Leucine
Valine

Question 4

What is required to stimulate optimal protein synthesis (mTORC1)?

Answer 4

• BCAA (especially Leucine, but also isoleucine, valine and glutamine)
• energy from CHO or protein to stimulate insulin production
• growth factors - important in growing children and pregnancy

Question 5

What is the protein that controls protein synthesis?

Answer 5

mTORC1

Question 6

What causes muscle atrophy (breakdown)?

Answer 6

• excess energy expenditure
• muscle inactivity
• ageing/illness
• ROS
• reduced energy/protein intake

Question 7

What causes muscle hypertrophy (growth) and how do these things stimulate it?

Answer 7

• testosterone
• muscle activity
• increased protein intake + sufficient energy/insulin

stimulates stem cells, muscle tears, and growth of muscle filaments to cause muscle hypertrophy

Question 8

What does negative nitrogen balance mean?

Answer 8

Muscle protein catabolism exceeds synthesis

Nitrogen excretion exceeds nitrogen intake = increased loss of body protein

Question 9

What causes negative nitrogen balance?

Answer 9

Illness
- additional requirements for repair/build up of tissue
- muscle loss due to inactivity
Malnutrition
Inadequate dietary protein - low/poor quality (missing some essential AA) and as we cant make part proteins we waste some AA

Question 10

What does positive nitrogen balance mean?

Answer 10

Muscle protein synthesis exceeds catabolism

Question 11

What happens to excess dietary protein?

Answer 11

• nitrogen excreted as urea
• used for energy in TCA cycle
• fatty acid synthesis from leucine (only ketogenic AA)
• gluconeogenesis

Question 12

Why is there an increased risk of dehydration with excess protein intake?

Answer 12

Due to increased urine production to excrete urea - also associated with loss of calcium

Question 13

What affects protein rate and amount of absorption?

Answer 13

• amount of protein present at once
• acid levels of the stomach
• whey protein - digested more quickly
• concentration of pepsin (breaks down proteins)

Question 14

Define protein quality.

Answer 14

The amount (concentration) of protein in a particular food, its supply of essential AA and its biological value

Question 15

What are some examples of complementary proteins?

Answer 15

Legumes + cereals, nuts & seeds - e.g. peanut butter and bread, baked beans and rice

Corn + legumes - e.g. corn tacos and beans, corn and chickpea salad

Question 16

What is the role of BCAAs?

Answer 16

• promote protein synthesis and turnover
• signalling pathways
• metabolism of glucose

Question 17

What is the evidence for BCAA supplementation?

Answer 17

It may assist post recovery but only if dietary intake is low

Question 18

What is the inborn error of BCAA metabolism?

Answer 18

Maple syrup urine disease (MSUD) - born without BCAA dehydrogenase enzyme so cant break down BCAA

• maple syrup (sweet) odour to urine & sweat
• high BCAA and ketones in blood

Treated by low BCAA diet

Question 19

What are purines?

Answer 19

Synthesized from glutamine - building block for DNA, RNA, ATP

Question 20

How are purines catabolised?

Answer 20

Catabolised into uric acid and excreted in urine

Question 21

What is gout (hyperuricaemia)?

Answer 21

Abnormal purine metabolism - excess uric acid in the blood

Question 22

What are the 4 purine metabolism pathways?

Answer 22

1. Making purines (synthetic pathways)
2. Converting purine compounds (conversion pathways)
3. Reusing purines (salvage pathways)
4. Disposing of excess purines (disposal pathways)

Question 23

What happens in gout?

Answer 23

Uric acid is deposited as sodium urate in the joints, kidney and urinary tract - symptoms similar to arthritis but may be a-symptomatic

Caused by genetics, and renal disease

Question 24

Who is gout more common in?

Answer 24

> 35 years (mature onset)

Males

Question 25

What is the most common pathway that leads to gout?

Answer 25

Abnormal purine salvage pathway - purines are not salvaged and excessive conversion to uric acid

Question 26

What are the 3 main contributors to gout?

Answer 26

• abnormal purine salvage pathway
• under excretion of uric acid
• dietary intake

Question 27

How much of purines come from endogenous sources vs exogenous sources?

Answer 27

Endogenous ~85% (overproduction and decreased excretion)

Exogenous ~15% from purine-rich foods

Question 28

What are the food sources of purines?

Answer 28

High - offal, seafood
Moderate - vegetables (asparagus, mushrooms)
Negligible - bread, cakes, biscuits

Question 29

What are the lifestyle recommendations for gout?

Answer 29

• limit high purine foods
• allow coffee - associated with decreased gout
• vitamin C supplementation
• limit alcohol
• weight reduction and exercise
• include plenty of fluids to excrete excess uric acid in urine
• include legumes, nuts, fruits and vegetables
• low fat dairy
• limit sweetened beverages and juice (fructose increases uric acid levels)

Question 30

How can drugs be used to treat gout?

Answer 30

• inhibit uric acid synthesis

- increase uric acid excretion