Nutrition

What you'll learn

This revision guide covers all aspects of nutrition required for Pearson Edexcel International IGCSE Biology. You'll master the components of a balanced diet, understand food tests, identify deficiency diseases, and explore how nutritional requirements vary across different groups. This topic is essential for Paper 1 and Paper 2, typically worth 5-8% of total marks.

Key terms and definitions

Nutrition — the process by which organisms obtain and use food substances for energy, growth, and maintaining health.

Balanced diet — a diet containing all seven food groups in correct proportions to meet the body's requirements for energy, growth, and health.

Malnutrition — a condition resulting from eating too much, too little, or an unbalanced intake of nutrients.

Vitamin — an organic compound required in small quantities for normal metabolic processes that cannot be synthesized by the body.

Mineral — an inorganic element required in small quantities for normal body function.

Deficiency disease — an illness caused by the lack of a particular nutrient in the diet.

Egestion — the removal of undigested food material (faeces) from the body.

Ingestion — the taking in of food through the mouth.

Core concepts

The seven components of a balanced diet

A balanced diet must contain appropriate proportions of seven essential components. The quantities required depend on age, sex, activity level, and pregnancy/lactation status.

Carbohydrates

• Main source of energy for cellular respiration
• Two types: simple sugars (glucose, fructose) and complex carbohydrates (starch, glycogen)
• Found in bread, rice, pasta, potatoes, cereals
• Excess stored as glycogen in liver and muscles, or converted to fat

Proteins

• Required for growth and repair of tissues
• Made from amino acids (20 types, 8 essential amino acids must come from diet)
• Sources include meat, fish, eggs, dairy, beans, nuts
• Cannot be stored; excess amino acids are deaminated in the liver

Lipids (fats and oils)

• Provide energy (more than twice the energy per gram compared to carbohydrates)
• Insulation and protection of organs
• Component of cell membranes
• Sources include butter, oils, nuts, oily fish, avocados
• Fat-soluble vitamins (A, D, E, K) require lipids for absorption

Vitamins

• Vitamin A (retinol): required for making light-sensitive pigment in retina, healthy skin and mucous membranes. Sources: liver, fish oils, dairy products, carrots. Deficiency causes night blindness.
• Vitamin C (ascorbic acid): required for healthy connective tissue, gums, and skin. Sources: citrus fruits, tomatoes, green vegetables. Deficiency causes scurvy (bleeding gums, poor wound healing).
• Vitamin D (calciferol): required for calcium absorption from intestine, maintaining healthy bones and teeth. Sources: oily fish, eggs, dairy, made in skin by UV light exposure. Deficiency causes rickets in children (bone deformities) and osteomalacia in adults (soft bones).

Minerals

• Calcium: required for strong bones and teeth, blood clotting, muscle contraction. Sources: milk, cheese, fish bones. Deficiency causes rickets and osteoporosis.
• Iron: required for haemoglobin formation in red blood cells. Sources: red meat, liver, dark green vegetables, fortified cereals. Deficiency causes anaemia (fatigue, weakness, pale skin).
• Sodium: required for nerve impulse transmission and fluid balance. Sources: table salt, processed foods. Excess linked to high blood pressure.

Water

• Makes up 60-70% of body mass
• Solvent for metabolic reactions
• Component of blood plasma, tissue fluid, and cytoplasm
• Temperature regulation through sweating
• Transport medium for nutrients and waste products
• Required: approximately 2 litres daily from drinks and food

Dietary fibre (roughage)

• Indigestible plant material (mainly cellulose)
• Provides bulk to food, stimulating peristalsis
• Prevents constipation and reduces risk of bowel cancer
• Sources: wholegrain cereals, vegetables, fruits
• Not absorbed but essential for healthy digestive system

Variation in dietary requirements

Different groups require different proportions of nutrients based on physiological needs.

Age-related requirements

• Children and adolescents: higher protein requirements for growth; calcium and vitamin D for bone development; more energy per kg body weight
• Adults: maintenance requirements only; energy needs decrease with age
• Elderly: may require more calcium and vitamin D to prevent osteoporosis; often lower energy requirements due to reduced activity

Sex differences

• Males generally require more energy due to larger average body size and muscle mass
• Females of reproductive age require more iron to replace losses during menstruation
• Pregnant women: increased requirements for protein (fetal growth), calcium (skeleton development), iron (increased blood volume), folic acid (prevents neural tube defects)
• Lactating women: increased energy, protein, and calcium requirements for milk production

Activity level

• Athletes and manual workers require significantly more carbohydrates and lipids for energy
• Protein requirements increase slightly for muscle repair after exercise
• Water requirements increase substantially during physical activity

Climate considerations

• Hot climates: increased water and mineral requirements due to sweating
• Caribbean and tropical regions: risk of dehydration higher; emphasis on fluid intake

Food tests

These practical tests identify specific nutrients in food samples. You must know the method, colour changes, and safety considerations.

Test for starch

• Reagent: iodine solution (brown/yellow colour)
• Positive result: blue-black colour
• Method: add 2-3 drops of iodine solution to food sample

Test for reducing sugars (glucose)

• Reagent: Benedict's solution (blue colour)
• Method: add Benedict's solution to food solution; heat in water bath at 80-100°C for 5 minutes
• Positive result: colour change from blue → green → yellow → orange → brick-red precipitate
• Intensity of colour indicates concentration of reducing sugar

Test for protein (Biuret test)

• Reagents: sodium hydroxide solution, then copper sulfate solution
• Method: add sodium hydroxide to food solution, then add copper sulfate drop by drop
• Positive result: purple/lilac colour
• Negative result: remains blue
• Safety: sodium hydroxide is corrosive; wear eye protection

Test for lipids (emulsion test)

• Reagent: ethanol, then water
• Method: dissolve food sample in ethanol; shake; pour liquid into water in clean test tube
• Positive result: white cloudy emulsion forms
• Negative result: solution remains clear
• Safety: ethanol is flammable; no naked flames

Malnutrition and deficiency diseases

Malnutrition occurs when the diet does not match the body's requirements. It includes both undernutrition and overnutrition.

Undernutrition

• Starvation: insufficient total food intake leads to severe weight loss, muscle wasting, weakened immune system
• Protein-energy malnutrition: particularly affects children in developing countries
• Kwashiorkor: protein deficiency despite adequate energy intake; symptoms include swollen abdomen (fluid retention), skin lesions, liver damage
• Marasmus: deficiency of both protein and energy; severe wasting of muscles and fat reserves

Overnutrition

• Obesity: excess body fat from consuming more energy than expended
• Body Mass Index (BMI) = mass (kg) ÷ [height (m)]²
• BMI > 30 indicates obesity
• Health risks: type 2 diabetes, cardiovascular disease, high blood pressure, joint problems, certain cancers
• Causes: excessive intake of high-energy foods (particularly fats and sugars), insufficient physical activity, genetic factors

Specific deficiency diseases

• Vitamin A deficiency: night blindness, increased infection risk, eventually permanent blindness
• Vitamin C deficiency: scurvy (bleeding gums, loose teeth, poor wound healing, joint pain)
• Vitamin D deficiency: rickets (children) with bowed legs and curved spine; osteomalacia (adults)
• Iron deficiency: anaemia with symptoms of tiredness, weakness, pale skin, shortness of breath
• Calcium deficiency: weak bones, increased fracture risk, osteoporosis in later life

Energy requirements and uses

Energy from food

• Measured in kilojoules (kJ) or kilocalories (kcal)
• 1 kcal = 4.2 kJ
• Carbohydrates and proteins: approximately 17 kJ/g
• Lipids: approximately 38 kJ/g
• Alcohol: approximately 29 kJ/g (not a nutrient)

Energy uses

• Basal metabolic rate (BMR): energy required for essential body processes at rest (heartbeat, breathing, cell metabolism, maintaining body temperature)
• Physical activity: varies enormously with type and intensity of exercise
• Growth: children and adolescents require energy for tissue synthesis
• Pregnancy and lactation: additional energy for fetal growth and milk production
• Thermoregulation: maintaining constant body temperature, especially in cold environments

Daily energy requirements (approximate values)

• Male adolescent (active): 12,000 kJ
• Female adolescent (active): 9,500 kJ
• Male adult (moderately active): 10,500 kJ
• Female adult (moderately active): 8,500 kJ
• Pregnant woman: +800-1,000 kJ
• Manual labourer: up to 15,000 kJ

Worked examples

Example 1: Dietary analysis question

Question: The table shows the daily energy requirements and actual energy intake for four individuals.

Individual	Daily requirement (kJ)	Actual intake (kJ)
A	10,500	8,000
B	9,500	11,200
C	8,500	8,600
D	12,000	9,500

(a) Which individual is most at risk of obesity? Explain your answer. [2 marks] (b) Suggest why individual D might be experiencing weight loss despite eating large quantities of food. [2 marks]

Mark scheme answer:

(a) Individual B [1 mark] Because their energy intake exceeds their energy requirement by the largest amount / they consume 1,700 kJ more than required [1 mark]

(b) Individual D has a high energy requirement (possibly due to high activity levels / being an athlete / manual work) [1 mark] Their intake is 2,500 kJ less than required, so stored fat/glycogen/protein is being used for energy [1 mark]

Example 2: Food test practical

Question: A student carried out food tests on three unknown solutions, X, Y and Z. The results are shown below:

Solution	Iodine test	Benedict's test	Biuret test
X	Blue-black	Blue (no change)	Purple
Y	Brown (no change)	Brick-red	Blue
Z	Blue-black	Orange	Purple

(a) Which nutrient(s) are present in solution Z? [2 marks] (b) Describe how the student should safely carry out the Biuret test. [3 marks]

Mark scheme answer:

(a) Starch [1 mark], reducing sugar, and protein [1 mark] (Accept: carbohydrate/glucose for reducing sugar; reject if only two nutrients identified)

(b) Add sodium hydroxide solution to the food sample / solution Z [1 mark] Then add copper sulfate solution drop by drop [1 mark] Wear eye protection / goggles because sodium hydroxide is corrosive [1 mark] (Accept: handle with care / avoid skin contact)

Example 3: Deficiency disease application

Question: In some developing countries, many children suffer from a deficiency disease characterised by swollen abdomens, skin lesions, and poor growth.

(a) Name this deficiency disease. [1 mark] (b) State which nutrient is lacking in the diet of these children. [1 mark] (c) Suggest two foods that could be added to their diet to prevent this disease. [2 marks] (d) Explain why this disease particularly affects children rather than adults. [2 marks]

Mark scheme answer:

(a) Kwashiorkor [1 mark]

(b) Protein [1 mark]

(c) Any two from: meat, fish, eggs, milk, beans/pulses, nuts [2 marks] (1 mark each; must be specific foods not food groups)

(d) Children have higher protein requirements because they are growing [1 mark] Children need protein for synthesis of new tissues / muscle / organs [1 mark] (Accept: children have smaller protein stores / adults have completed growth)

Common mistakes and how to avoid them

• Confusing egestion with excretion: Egestion is removal of undigested food material through the anus; excretion is removal of metabolic waste products (like urea, CO₂). Faeces are egested, not excreted, because they have never been inside body cells.

• Saying fibre is digested or absorbed: Fibre (cellulose) cannot be digested by human enzymes. It provides bulk and stimulates peristalsis but passes through unchanged. Don't write that fibre is "broken down" or "absorbed."

• Mixing up deficiency diseases: Learn the specific vitamin/mineral linked to each disease. Night blindness = vitamin A; scurvy = vitamin C; rickets = vitamin D or calcium; anaemia = iron. Don't guess or confuse them in exam answers.

• Vague answers about energy requirements: Be specific about why different groups need different amounts. Don't just write "pregnant women need more nutrients" — explain that they need more protein for fetal growth, more iron for increased blood volume, more calcium for skeleton development.

• Food test colour changes: Learn the exact colour changes, especially for Benedict's test (blue → green → yellow → orange → brick-red). "It turns red" is insufficient; state the starting colour and the positive result colour clearly.

• BMI calculation errors: Remember to square the height: BMI = mass (kg) ÷ [height (m)]². Many students forget to square the height or use height in cm instead of metres.

Exam technique for "Nutrition"

• Command words matter: "State" requires a brief answer with no explanation (1 mark). "Explain" requires a reason or mechanism (usually 2+ marks). "Describe" requires an account of what happens without needing to explain why.

• Food test questions: Always include both the reagent name AND the colour change for full marks. State what colour the reagent starts as and what positive result looks like. For Benedict's test, mention heating in a water bath.

• Deficiency disease questions: Structure answers with three elements: (1) name of deficiency disease, (2) nutrient lacking, (3) symptoms observed. For full explanation marks, link the nutrient's function to why those symptoms appear.

• Calculation questions: Show your working clearly for BMI or energy calculations. Include units in your final answer. Round to appropriate significant figures (usually 2 or 3). If a calculation seems wrong, check you've used the correct units (kg not g, metres not cm).

Quick revision summary

A balanced diet contains seven components in appropriate proportions: carbohydrates, proteins, lipids, vitamins, minerals, water, and fibre. Requirements vary with age, sex, activity level, and pregnancy status. Food tests identify nutrients using specific reagents and colour changes. Malnutrition includes both deficiency diseases (scurvy, rickets, anaemia, kwashiorkor) and overnutrition leading to obesity. Energy from food supports basal metabolism, physical activity, growth, and thermoregulation. Understanding nutritional needs and their consequences is essential for public health and forms a key foundation for human biology topics.