Protein Flashcards
What is the RDI for protein?
0.8-1.0g/kg/day
What are the essential amino acids that must be supplied in food?
Histidine (in children) Isoleucine Leucine Valine Lysine Methionine Phenylalanine Threonine Tryptophan
What are the 3 BCAA?
Isoleucine
Leucine
Valine
What is required to stimulate optimal protein synthesis (mTORC1)?
- 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
What is the protein that controls protein synthesis?
mTORC1
What causes muscle atrophy (breakdown)?
- excess energy expenditure
- muscle inactivity
- ageing/illness
- ROS
- reduced energy/protein intake
What causes muscle hypertrophy (growth) and how do these things stimulate it?
- testosterone
- muscle activity
- increased protein intake + sufficient energy/insulin
stimulates stem cells, muscle tears, and growth of muscle filaments to cause muscle hypertrophy
What does negative nitrogen balance mean?
Muscle protein catabolism exceeds synthesis
Nitrogen excretion exceeds nitrogen intake = increased loss of body protein
What causes negative nitrogen balance?
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
What does positive nitrogen balance mean?
Muscle protein synthesis exceeds catabolism
What happens to excess dietary protein?
- nitrogen excreted as urea
- used for energy in TCA cycle
- fatty acid synthesis from leucine (only ketogenic AA)
- gluconeogenesis
Why is there an increased risk of dehydration with excess protein intake?
Due to increased urine production to excrete urea - also associated with loss of calcium
What affects protein rate and amount of absorption?
- amount of protein present at once
- acid levels of the stomach
- whey protein - digested more quickly
- concentration of pepsin (breaks down proteins)
Define protein quality.
The amount (concentration) of protein in a particular food, its supply of essential AA and its biological value
What are some examples of complementary proteins?
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
What is the role of BCAAs?
- promote protein synthesis and turnover
- signalling pathways
- metabolism of glucose
What is the evidence for BCAA supplementation?
It may assist post recovery but only if dietary intake is low
What is the inborn error of BCAA metabolism?
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
What are purines?
Synthesized from glutamine - building block for DNA, RNA, ATP
How are purines catabolised?
Catabolised into uric acid and excreted in urine
What is gout (hyperuricaemia)?
Abnormal purine metabolism - excess uric acid in the blood
What are the 4 purine metabolism pathways?
- Making purines (synthetic pathways)
- Converting purine compounds (conversion pathways)
- Reusing purines (salvage pathways)
- Disposing of excess purines (disposal pathways)
What happens in gout?
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
Who is gout more common in?
> 35 years (mature onset)
Males
What is the most common pathway that leads to gout?
Abnormal purine salvage pathway - purines are not salvaged and excessive conversion to uric acid
What are the 3 main contributors to gout?
- abnormal purine salvage pathway
- under excretion of uric acid
- dietary intake
How much of purines come from endogenous sources vs exogenous sources?
Endogenous ~85% (overproduction and decreased excretion)
Exogenous ~15% from purine-rich foods
What are the food sources of purines?
High - offal, seafood
Moderate - vegetables (asparagus, mushrooms)
Negligible - bread, cakes, biscuits
What are the lifestyle recommendations for gout?
- 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)
How can drugs be used to treat gout?
- inhibit uric acid synthesis
- increase uric acid excretion
