Protein

what are amino acids

building blocks of proteins (proteinogenic in human nutrition)

what are BCAAs

Branched Chain Amino Acids (valine, leucine, isoleucine), most abundant in complete protein, primarily used by muscles for energy, and promote muscle protein synthesis

how many amino acids are made into human protein

20

what are essential amino acids

9AAs that must come from diet: phenylalanine, valine, threonine, tryptophan, isoleucine, methioine, histidine, leucine, and lysine (PVT TIM HLL)

what are conditionally essential amino acids

6 AAs needed in certain conditions: arginine, cysteine, glutamine, glycine, proline, tyrosine

what starts protein digestion

chewing and HCL in stomach

what does HCL do to proteins

unfolds them into long polypeptides and activates pepsin

what is pepsin

stomach enzyme that breaks down protein

where is most protein digestion completed

small intestine, with pancreatic enzymes -> ~90% amino acids absorbed

how are AAs transported after absorption

through the portal vein to the liver

what can proteins be used for besides building tissue

catabolized for energy or used to make glucose

in low energy availability, what tissue is sacrificed for energy

skeletal muscle

what must happen before AAs enter energy pathways

deamination (removal of nitrogen groups)

where can AAs enter for energy production

different entry points of the Krebs cycle

what is protein turnover

constant breakdown and rebuilding of proteins

when is turnover highest

during stress or exercise

main protein functions

enzymes, antibodies, pumps/regulators, fluid balance, acid-base balance, and movement

what is the most abundant protein in the body

collagen

what proteins are responsible for movement

motor proteins

where is the code for protein synthesis stored

DNA -> transcribes to mRNA -> translated at ribosomes

what must be present for protein synthesis to complete

all amino acids

if an AA is missing, what happens

skeletal muscle is broken down to supply it

what is the AMDR for protein

10-35% of daily calories

general protein intake guidelines

0.8 g/kg body weight (athletes: 1.2 g/kg+)

what is more accurate: % calories or g/kg

g/kg body weight

what are the highest quality proteins

animal products and soybeans protein isolate

what is whey protein

fast-digesting, high in BCAAs

what is casein protein

slower digesting, similar to whey

what is egg protein

high quality, good for those avoiding dairy

what determines protein quality

amount of protein and digestibility/absorption

functions of protein in athletes

build muscle, promote adaptations, preserve lean mass, strengthen non-muscle tissues

athlete protein intake guidelines

1.2-2.0 g/kg (up to 3 g/kg for physique athletes)

180 lb athlete protein needs

90.9 kg -> 109-182 g protein/day

best way to distribute protein

spread throughout day (0.25-0.3 g/kg per meal), avoid backloading

what increases protein synthesis

exercise novelty, hormones post-workout, injury/illness recovery, positive energy balance

what amino acid triggers muscle protein synthesis (MPS)

700-3,000 mg per meal (with ~10 g essential amino acids)

what are optimal protein sources for MPS

whey, dairy, and other complete proteins