Protein

Not one nutrient but the source of the amino acids your body cannot make and must obtain — the raw material for muscle, enzymes, antibodies and hormones.

Supplies the twenty amino acids used to build everything structural and functional — muscle, enzymes, antibodies, hormones. Nine of them cannot be made by the body and must come from food.

• Meat, fish and eggs
• Dairy
• Legumes and lentils
• Tofu and tempeh
• Nuts and seeds
• Whole grains

Plant proteins are individually incomplete but combine perfectly well across a day — the old "combining at every meal" advice was overturned decades ago.

0.8 g per kg body weight minimum · 1.0–1.2 g/kg is often suggested for older adults for most adults. The upper limit, past which harm becomes likely, is None established.

Reference intakes are population figures. Pregnancy, illness, age and medication all move an individual’s needs, which is one of several reasons this page is information rather than advice.

A sustained shortage has a name here: Kwashiorkor · Marasmus. That is worth pausing on — nutrients whose deficiency earned a name are the ones where the consequences were severe enough, historically, to be described as a disease.

Most at risk: Older adults, who need more than younger adults and often eat less. Also illness, recovery from surgery, and very restricted diets.

Uncommon in high-income countries outside illness, but under-recognised in older adults, in people recovering from surgery or serious illness, and in very restricted diets. Requirements rise with age, not down.

Muscle wasting, swelling, poor wound healing, hair and skin changes, and weakened immunity. Severe forms are diseases of famine.

Every sign here has other, often likelier, explanations. A list of symptoms is a reason to look into something, never a diagnosis.

Serum albumin is often used as a proxy and is a poor one — it falls with inflammation more readily than with intake. Weight history, grip strength and muscle mass tell you more.

Meat, fish, eggs, dairy, legumes, tofu, tempeh, nuts and seeds. Spreading protein across meals uses it better than concentrating it at dinner. Plant sources combine over a day; they do not need combining at a single meal.

Powders are food, not medicine, and useful mainly for convenience or when appetite is poor. Whey, casein, soy and pea all work. Very high intakes have not shown benefit in people with healthy kidneys, and are not advisable in those without.

Well tolerated in healthy people. In established kidney disease, high intake accelerates decline — which is where the general "protein harms kidneys" idea comes from, and it does not apply to healthy kidneys.