What are the main nutrients studied in O-Level Food and Nutrition?

The syllabus groups nutrients into the macronutrients needed in large amounts (protein, carbohydrate and fat), the micronutrients needed in small amounts (vitamins and minerals) and water. You must know the functions, food sources and deficiency effects of each, and be able to apply them when judging or planning a diet. Protein provides 17 kJ per gram, carbohydrate 17 kJ per gram and fat 37 kJ per gram, so fat is the most energy-dense nutrient.

What is the difference between high and low biological value protein?

High biological value (HBV) protein contains all the essential amino acids the body cannot make, in the proportions it needs; these come mainly from animal foods such as meat, fish, eggs, milk and cheese, plus soya. Low biological value (LBV) protein is missing one or more essential amino acids and comes from plant foods such as cereals, nuts and pulses. Vegetarians use protein complementation, combining two LBV foods such as rice and beans, so the missing amino acids in one are supplied by the other.

Why are some vitamins lost during cooking?

Water-soluble vitamins, the B group and vitamin C, dissolve into cooking water and are easily destroyed by heat, light and exposure to air. Vitamin C is the most fragile and is lost when vegetables are cut early, soaked, overcooked or kept hot for a long time. Fat-soluble vitamins (A, D, E and K) are far more stable to cooking because they are not lost into water, so the practical lesson is to steam or stir-fry vegetables quickly and serve them straight away.

Why is water counted as a nutrient if it gives no energy?

Water provides no energy and no kilojoules, but it is essential because it makes up about two-thirds of the body, transports nutrients and waste in the blood, regulates body temperature through sweating, and is the medium for almost every chemical reaction in cells. An adult needs roughly six to eight glasses (about 1.5 to 2 litres) a day, more in Singapore's hot, humid climate or during exercise, so it is treated as a nutrient even though it yields nothing on the energy scale.

Which minerals does the O-Level syllabus focus on?

The key minerals are calcium, for strong bones and teeth and for blood clotting, with a deficiency causing rickets in children and osteoporosis in adults; iron, needed to make haemoglobin in red blood cells, with a deficiency causing anaemia; and sodium, which controls water balance and nerve function but raises blood pressure when eaten in excess. Calcium absorption depends on vitamin D, and iron absorption is improved by vitamin C, so minerals and vitamins must be considered together.

SingaporeNutrition & Food Science

Nutrients and their functions: the macronutrients, vitamins, minerals and water that the body needs and what each one does

An O-Level Food and Nutrition (SEAB 6087) overview of nutrients and their functions: the three macronutrients (protein, carbohydrate and fat) and the energy they provide, the fat-soluble and water-soluble vitamins, the key minerals, and water as an essential nutrient, with links to every dot point and a worked nutrient-analysis.

Generated by Claude Opus 4.89 min readSEAB-6087Updated 2026-06-13

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this module demands
The three macronutrients and their energy
The micronutrients: vitamins, minerals and water
How the nutrients are examined
Check your knowledge

What this module demands

Nutrients are the building blocks of everything else in Food and Nutrition (SEAB 6087). Before you can plan a balanced diet, judge a diet-related disease or adapt a recipe for health, you must know what each nutrient does, where it is found and what happens when it is missing. The Paper 1 written examination tests this in Section A short-answer questions ("state two functions of calcium"), in the Section B data-response questions that ask you to read a nutrition panel, and in the Section C essays that ask you to justify the nutrients a particular person needs. This overview ties the macronutrients, vitamins, minerals and water together and links to every dot point in the module.

You can see the full set of dot points at /sg-o-level/nutrition-and-food-science/syllabus/nutrients-and-their-functions.

The three macronutrients and their energy

Start with the big picture in the macronutrients overview. The three macronutrients are needed in large amounts: protein for growth and repair, carbohydrate for energy, and fat for concentrated energy and insulation. The energy values are worth memorising exactly because calculations depend on them: protein gives 17 kJ per gram, carbohydrate gives 17 kJ per gram, and fat gives 37 kJ per gram. Fat is therefore more than twice as energy-dense as the other two, which is why fatty foods raise the energy content of a meal so quickly.

Protein, its functions and sources is built from amino acids and is the body's only source of nitrogen, used to build and repair muscle, skin, enzymes and antibodies. The key distinction for marks is high biological value (HBV) protein from animal foods and soya, which contains all essential amino acids, versus low biological value (LBV) protein from plants, which is missing one or more; combining two LBV foods is called complementation.

Carbohydrates and dietary fibre splits into sugars, starches and fibre. Sugars and starches are the body's main energy source, while dietary fibre gives almost no energy yet is essential because it adds bulk, prevents constipation and helps you feel full. This is the natural place to argue for wholegrain over refined choices, which links forward to diet-related disease.

Fats and oils provide concentrated energy, insulate the body, protect organs and carry the fat-soluble vitamins. The health distinction the examiner wants is saturated fat, solid at room temperature and linked to raised blood cholesterol and heart disease, versus unsaturated fat, usually liquid and the healthier choice.

The micronutrients: vitamins, minerals and water

Vitamins are needed in tiny amounts but their absence causes specific deficiency diseases. Split them into fat-soluble (A, D, E, K), which the body can store, and water-soluble (B group and C), which are not stored and so are needed regularly. Learn the headline functions and deficiencies: vitamin A for vision (deficiency causes night blindness), vitamin D for calcium absorption (deficiency causes rickets), vitamin C for healthy connective tissue and iron absorption (deficiency causes scurvy), and the B group for releasing energy from food.

Minerals and water covers the three minerals the syllabus emphasises: calcium for bones, teeth and blood clotting (deficiency causes rickets or osteoporosis); iron for haemoglobin in red blood cells (deficiency causes anaemia); and sodium for fluid balance and nerve function (excess raises blood pressure). Water closes the module: it gives no energy but transports substances, regulates temperature and is the medium for chemical reactions, with a need of about 1.5 to 2 litres a day, more in Singapore's climate.

How the nutrients are examined

State functions and sources precisely. Section A rewards exact recall: name the deficiency disease, give a real food source, state the function in one clear sentence. "Calcium is for health" earns nothing; "calcium builds strong bones and teeth and is found in milk and cheese" earns the mark.
Read and compare nutrition data. Section B gives a nutrition panel or a table and asks you to identify which food is higher in fat or fibre, or to calculate energy. Use the energy values (17, 17 and 37 kJ per gram).
Justify nutrients for a person. Section C essays describe someone (a pregnant woman, a growing teenager, an older adult) and ask which nutrients they need and why. Match the nutrient to the life stage and explain the reason.

Analysing the nutrients in a chicken-and-rice meal

A student eats a plate containing 30 g of protein, 70 g of carbohydrate and 15 g of fat. Work out the energy it provides and judge how balanced it is.

step Recall the energy values

Protein and carbohydrate each provide 17 kJ per gram; fat provides 37 kJ per gram. These are the fixed values from the macronutrients dot point.

step Calculate the energy from each macronutrient

Protein: 30 g x 17 = 510 kJ. Carbohydrate: 70 g x 17 = 1190 kJ. Fat: 15 g x 37 = 555 kJ.

step Total the energy

510 + 1190 + 555 = 2255 kJ for the meal. Carbohydrate supplies the most energy, which is appropriate for a main meal that should be built on a wholegrain or rice base.

step Judge the balance and improve it

The fat (15 g) contributes about a quarter of the energy from only a small mass, showing how energy-dense fat is. The meal has good protein for repair and plenty of carbohydrate for energy, but it lacks fibre, vitamins and minerals because there are no vegetables. Adding a serving of stir-fried greens supplies vitamin C, fibre and minerals, and a glass of water replaces fluid lost in Singapore's heat, turning an adequate meal into a balanced one.

Nutrients are grouped into macronutrients needed in large amounts (protein for growth and repair, carbohydrate for energy, fat for concentrated energy and insulation), micronutrients needed in small amounts (vitamins and minerals), and water. Protein and carbohydrate each provide 17 kJ per gram and fat provides 37 kJ per gram. Protein is high biological value from animal foods and soya or low biological value from plants. Vitamins split into fat-soluble (A, D, E, K) and water-soluble (B and C), the latter easily lost in cooking. The key minerals are calcium for bones, iron for haemoglobin and sodium for fluid balance, while water gives no energy but transports substances and regulates temperature. The strongest answers pair nutrients, such as vitamin D with calcium and vitamin C with iron.

Check your knowledge

A mix of recall and application questions covering the nutrients. Attempt them, then check against the solutions.

State the energy value, in kJ per gram, of protein, carbohydrate and fat. (3 marks)
Explain the difference between high and low biological value protein and give one food source of each. (3 marks)
Name the deficiency disease caused by a lack of iron and explain why iron is needed. (2 marks)
Explain why water-soluble vitamins are easily lost during cooking and give one way to reduce the loss. (2 marks)
Explain why water is classed as an essential nutrient even though it provides no energy. (2 marks)

Solutions

Q1: Protein 17 kJ per gram, carbohydrate 17 kJ per gram, fat 37 kJ per gram. Fat is the most energy-dense, providing more than twice the energy of the other two for the same mass.
Q2: High biological value protein contains all the essential amino acids the body needs and comes from animal foods such as fish, eggs or milk, or from soya. Low biological value protein is missing one or more essential amino acids and comes from plant foods such as rice, nuts or beans. (Any one valid source for each.)
Q3: A lack of iron causes anaemia. Iron is needed to make haemoglobin in red blood cells, which carries oxygen around the body; without enough, a person feels tired and breathless.
Q4: Water-soluble vitamins (B group and C) dissolve into cooking water and are destroyed by heat, so boiling for a long time leaches them away. To reduce loss, steam or stir-fry vegetables quickly and serve them straight away, or use the cooking water in a sauce or soup.
Q5: Water gives no energy but is essential because it makes up about two-thirds of the body, transports nutrients and waste in the blood, regulates body temperature through sweating, and is the medium in which the chemical reactions of the cells take place.

Sources & how we know this

Singapore-Cambridge GCE O-Level Food and Nutrition (Syllabus 6087) — Singapore Examinations and Assessment Board (2026)
My Healthy Plate and dietary guidelines — Health Promotion Board, Singapore (2026)