Pancreatic enzymes cut them into short chains in the small intestine.
Brush-border enzymes finish the job; amino acids are absorbed.
Cells read DNA and link amino acids into new proteins.
What does Protein do?
Provides amino acids — 9 of which are essential because the body can't make them — to build and repair tissue and make enzymes, hormones and antibodies. Provides about 4 kcal per gram.
Where does Protein act in the body?
Every tissue. Muscle is the largest protein store; the liver and gut also turn protein over quickly.
Which foods contain Protein?
Meat, fish, eggs, dairy, legumes (lentils, beans, soy), nuts, seeds and whole grains. Combining plant proteins across the day covers all essential amino acids.
How much Protein do adults need?
RDA: 0.8 g per kg body weight per day for adults. AMDR: 10–35% of energy. No upper limit set.
What happens with too little Protein?
Severe deficiency causes muscle loss, swelling and poor immunity — rare in high-income countries outside illness or very restricted diets.
Can you get too much Protein?
No established harm in healthy people at typical high intakes. People with kidney disease may need limits set by a clinician.
What does Protein interact with?
Muscle building responds to protein together with resistance exercise — protein alone doesn't build muscle.
What is known and unknown about Protein?
Requirements for basic needs are well established. Optimal intakes for older adults and athletes (often 1.2–2.0 g/kg) are debated.
Evidence & sources
The adult RDA for protein is 0.8 g per kg of body weight per day. Evidence: regulatory. Known: Set to cover the needs of nearly all healthy adults. Unknown: Optimal intakes for older adults and athletes are debated. Source: National Academies (Institute of Medicine), DRIs for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (2002/2005).
Protein supplementation increases gains in muscle strength and size from resistance training, with benefits plateauing around 1.6 g/kg/day. Evidence: moderate. Known: Meta-analysis of 49 randomized trials. Unknown: Effects are modest; individual response varies. Source: Morton et al., British Journal of Sports Medicine, A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains (2018).