Carbohydrate

The body’s most readily used fuel, and the brain’s preferred one. Type and context matter far more than quantity in isolation — wholegrains, legumes and fruit behave very differently from refined starch and sugar.

The body’s preferred fuel, and the only fuel the brain uses in quantity under normal conditions.

• Whole grains
• Potatoes and root vegetables
• Fruit
• Legumes
• Dairy (lactose)

130 g minimum for brain function · 45–65% of energy typically for most adults. The upper limit, past which harm becomes likely, is None; free sugars suggested under 10% of energy.

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.

Most at risk: Not a deficiency seen in practice.

No essential requirement in the strict sense, since the body can make glucose from other sources. Very low intake causes fatigue, constipation and difficulty concentrating in some people, and is not appropriate for everyone.

Not essential in the strict sense — the body can make glucose from protein and fat. Very low intake causes fatigue, constipation and bad breath as ketones rise.

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

Not tested as a nutrient. Blood glucose and HbA1c measure how your body is handling it, which is a different question.

Wholegrains, legumes, fruit and vegetables over refined starches and sugars. Eating carbohydrate with protein, fat or fibre slows the rise in blood glucose noticeably.

Not supplemented outside sports nutrition, where timing and form are the point rather than total intake.

Excess free sugar contributes to tooth decay, weight gain and metabolic problems. Whole-food carbohydrate behaves quite differently from refined sugar.