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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key concept
A balanced diet contains adequate amounts of all nutrients: carbohydrates (energy), proteins (growth and repair), lipids (energy storage and insulation), vitamins (various metabolic functions), minerals (various structural and metabolic roles), water (solvent and transport) and dietary fibre (prevents constipation).
Understanding what constitutes a balanced diet is the foundation of the human nutrition topic. You need to name each nutrient group, give food sources, state functions, and explain what happens if there is a deficiency or excess. Examiners also test whether you can evaluate diets and suggest improvements.
The Seven Components of a Balanced Diet
Nutrient
Function
Food sources
Carbohydrates
Main energy source
Rice, bread, pasta, potatoes, sugar
Proteins
Growth and repair of tissues; making enzymes, antibodies, hormones
Meat, fish, eggs, beans, lentils, dairy
Lipids (fats/oils)
Energy store; insulation; protection of organs; cell membranes
Butter, oil, nuts, cheese, fatty fish
Vitamins
Various metabolic functions (see below)
Fruits, vegetables, dairy, liver
Minerals
Various structural and metabolic roles (see below)
Meat, dairy, leafy greens, whole grains
Water
Solvent for reactions; transport medium; temperature regulation
Drinks, foods with high water content
Dietary fibre (roughage)
Adds bulk to food; stimulates peristalsis; prevents constipation
Whole grains, vegetables, fruit, bran
What Makes a Diet "Balanced"?
A balanced diet provides:
The right amount of energy for the individual's needs: varies by age, sex, activity level and health.
All essential nutrients in the correct proportions.
Consequences of an unbalanced diet:
Too much energy (excess carbohydrates/lipids) → obesity → increased risk of type 2 diabetes, heart disease, high blood pressure, some cancers.
Too little energy → weight loss, fatigue, weakened immune system, starvation.
Too little protein (protein-energy malnutrition) → kwashiorkor (swollen abdomen, muscle wasting) in severe cases.
Specific vitamin/mineral deficiencies → specific deficiency diseases (covered in the next subtopic).
Energy Requirements Vary
Different people need different amounts of energy:
Active people need more energy than sedentary people: muscle contraction uses a lot of energy.
Growing children and teenagers need more protein for growth and more energy overall.
Pregnant women need extra protein, iron, calcium and folic acid for the developing baby.
Males generally need more energy than females of the same age because they tend to have more muscle mass.
Exam tip: When evaluating a diet, compare the person's intake with their requirements based on their age, sex and activity level. Don't just say "they need more vegetables": specify which nutrient is lacking and why.
Try a focused question (3 marks)
A teenage athlete has a diet high in carbohydrates and proteins but low in vitamin C. Suggest why this diet may cause problems. (3 marks)
Show the answer and marking guidance
Vitamin C is needed for maintaining healthy skin and gums / making connective tissue.
A deficiency in vitamin C can cause scurvy: symptoms include bleeding gums, slow wound healing, and fatigue.
Although the diet provides enough energy (carbohydrates) and protein for growth/repair, the lack of vitamin C means tissues cannot be properly maintained.
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Saying fibre is a nutrient that is digested: fibre is NOT digested; it passes through the gut, adding bulk.
Forgetting water as a component of a balanced diet: it is essential and often overlooked.
Not linking excess food intake to specific health problems: be specific (obesity → type 2 diabetes, not just "getting fat").