Diet

Biology · Human nutrition. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

Test this topic free All Biology topics

The idea

Food gives the body energy, materials for growth and repair, and substances that keep it healthy. A balanced diet contains all the nutrients, in the right proportions for the needs of that person: carbohydrates, lipids (fats), proteins, vitamins, mineral salts, fibre and water.

Needs are not the same for everyone. A person who is young and growing, very active or pregnant needs more energy and more of some nutrients than a small, inactive adult.

If one nutrient is missing for a long time, a deficiency disease develops. Each has its own symptoms, so you can work back from the symptoms to the missing nutrient.

Rules to remember

Carbohydrates (rice, bread, potatoes, sugar): the main source of energy
Lipids (butter, oils, nuts, fatty meat): energy store, insulation, making cell membranes
Proteins (meat, fish, eggs, milk, pulses): growth and repair; making enzymes and antibodies
Vitamin C (citrus fruits, fresh vegetables): lack causes scurvy (bleeding gums, wounds heal slowly)
Vitamin D (oily fish, eggs; also made in skin in sunlight) and calcium (milk, cheese): strong bones and teeth; lack of either causes rickets (soft, bent bones)
Iron (red meat, liver, green leafy vegetables): making haemoglobin; lack causes anaemia (tiredness, pale skin)
Fibre (vegetables, fruit, wholegrain cereals) adds bulk and prevents constipation; water is the solvent for transport and for reactions in cells

Common mistake

A balanced diet does not mean equal amounts of every nutrient, and it does not mean eating a lot. It means the right proportions for that person's needs.

Worked example

A boy eats mainly white bread, meat, eggs and milk, and drinks orange juice every day. He often has constipation. Which component of a balanced diet is he most likely lacking?

Bread gives carbohydrate; meat, eggs and milk give protein, lipid, iron and calcium; orange juice gives vitamin C.
None of these foods contains much plant cell wall material, so the diet is low in fibre.
Fibre adds bulk to food so the gut muscles can push it along. Without it, faeces move slowly and become hard.

Answer: Fibre (roughage). He should eat more vegetables, fruit and wholegrain foods.

Ask about this

Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.

Read the full notes

Nutrition in Animals

Keep going

← Transpiration and translocation Human digestive system →Take a Biology test