A Balanced Diet — Nutrition & Digestion | IGCSE Biology

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 16% of your exam marks.

stable

Very High

Stable16%

Enzymes in digestion and the role of digestive structures appear regularly across both papers.

A balanced diet contains all of the necessary nutrient groups in the right proportions. The seven essential groups are:

Food group	Function in the body	Common food sources
Carbohydrates	Main source of energy	Bread, rice, pasta, potatoes, cereals
Proteins	Growth and repair of tissues; making enzymes, antibodies, hormones	Meat, fish, eggs, beans, nuts, dairy
Lipids	Long-term energy storage and insulation; part of every cell membrane	Butter, oils, nuts, oily fish
Dietary fibre	Provides roughage so the muscles of the gut can push food along	Vegetables, fruit, wholegrain bread, beans
Vitamins	Needed in tiny amounts to keep the body working	Fruit, vegetables, dairy, meat
Minerals	Needed in tiny amounts for specific roles (e.g. calcium for bones, iron for blood)	Dairy, meat, leafy green vegetables
Water	Solvent for chemical reactions; transport medium in blood; lost as sweat and urine	Drinks, fruit, vegetables

Key vitamins and minerals to know

Vitamin A is used to make the pigment in the retina that lets you see in dim light. A deficiency causes night blindness. Found in liver, dairy, leafy green vegetables and orange-yellow vegetables.
Vitamin C is needed to make collagen, the protein that holds skin, gums and connective tissues together. Severe deficiency causes scurvy (bleeding gums, slow wound healing). Found in citrus fruits, peppers and green vegetables.
Vitamin D helps the body absorb calcium from food and is needed for strong bones and teeth. Severe childhood deficiency causes rickets (soft, bowed bones). Found in oily fish and dairy products, and made by the skin in sunlight.
Calcium is needed for bones and teeth, and helps blood clot at a wound. A long-term deficiency leads to osteoporosis (weak, brittle bones). Found in milk, cheese and yoghurt.
Iron is needed to make haemoglobin in red blood cells. A deficiency causes anaemia (tiredness, pale skin, breathlessness) because the blood cannot carry enough oxygen. Found in red meat, liver, leafy green vegetables.

Why energy needs vary

Different people need different amounts of energy depending on:

Age: children and teenagers need a lot of energy for growth. An adult's energy needs slowly fall after middle age.
Activity level: a person who exercises a lot or does manual work respires faster, so they need more energy.
Sex: on average, men have more muscle and so use more energy than women of the same mass.
Pregnancy and breastfeeding: a pregnant woman needs extra energy, protein, calcium and iron to build the fetus's body and her own larger blood supply. A breastfeeding mother needs extra energy and calcium to produce milk.

An unbalanced diet causes malnutrition. Too little of one group causes a deficiency disease (e.g. scurvy, rickets, anaemia). Too much energy intake versus output causes obesity, which raises the risk of heart disease, type 2 diabetes and some cancers.