What is a balanced diet in O-Level Food and Nutrition?

A balanced diet is one that provides all the nutrients the body needs, in the right amounts and proportions, with enough energy but not too much. In Singapore it is translated into practice by My Healthy Plate, which divides the plate into a quarter wholegrains, a quarter meat and others (protein), and half fruit and vegetables, plus water rather than sugary drinks. A balanced diet supplies protein, carbohydrate, fat, vitamins, minerals, fibre and water and reduces the risk of diet-related disease.

What is energy balance and what happens when it is wrong?

Energy balance is the relationship between the energy you take in from food and the energy you use up through basal metabolic rate (BMR) and activity. When intake equals output, weight stays the same. An energy surplus, where intake is greater than output, is stored as fat and leads to weight gain and eventually obesity. An energy deficit, where output is greater than intake, draws on body stores and leads to weight loss. This is the central principle behind weight management.

Which diseases are linked to a poor diet?

The main diet-related diseases in the syllabus are obesity (from a long-term energy surplus), coronary heart disease (linked to too much saturated fat and salt raising blood cholesterol and pressure), type 2 diabetes (linked to obesity and a high intake of sugar and refined carbohydrate) and high blood pressure or hypertension (linked to a high salt intake). All can be reduced by a balanced diet lower in saturated fat, sugar and salt and higher in fibre, fruit and vegetables.

How is body mass index (BMI) calculated and used?

BMI is calculated as weight in kilograms divided by height in metres squared, that is BMI = weight / (height x height). It classifies a person as underweight, healthy weight, overweight or obese, and is a quick screening tool used in weight management. It has limits: a very muscular person can have a high BMI without excess fat, so BMI is judged alongside other measures rather than on its own.

How do nutritional needs change across the life cycle?

Children and teenagers need extra protein, calcium and iron for rapid growth and bone development, and teenagers need a lot of energy. Pregnant women need more folate, iron, calcium and protein to support the developing baby. Adults need enough to maintain the body without an energy surplus. Older adults need less energy as activity falls but still need calcium and vitamin D to protect bones and fibre to prevent constipation, so the balance of nutrients shifts with each stage.

SingaporeNutrition & Food Science

Diet, health and special needs: balanced diet, energy balance, diet-related diseases, weight management and adapting meals for special groups

An O-Level Food and Nutrition (SEAB 6087) overview of diet and health: what makes a diet balanced, energy balance and basal metabolic rate, the diet-related diseases, weight management and BMI, changing needs across the life cycle and special dietary needs, with links to every dot point and a worked energy-balance walkthrough.

Generated by Claude Opus 4.88 min readSEAB-6087Updated 2026-06-13

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

Jump to a section

What this module demands
The balanced diet and energy balance
Diet, disease and weight
Tailoring the diet to the person
How diet and health is examined
Check your knowledge

What this module demands

This module turns nutrition science into health. Having learnt the nutrients, you now apply them: deciding what a balanced diet looks like, understanding how energy balance controls body weight, explaining how a poor diet causes disease over time, and adapting meals for people with special needs. The Paper 1 written examination loves this material because it produces strong Section C essays ("explain how a teenager's diet should differ from an older adult's") and Section B data-response questions on energy balance and BMI. This overview links every dot point and shows how the ideas connect.

See the full set of dot points at /sg-o-level/nutrition-and-food-science/syllabus/diet-health-and-special-needs.

The balanced diet and energy balance

Begin with the balanced diet and the food pyramid. A balanced diet provides all nutrients in the right proportions with enough but not too much energy. In Singapore the practical guide is My Healthy Plate: half the plate fruit and vegetables, a quarter wholegrains, a quarter meat and others, with water as the drink. This is the framework every meal-planning answer should reference.

Energy balance and basal metabolic rate is the quantitative spine of the module. Energy in (from food) is compared with energy out (basal metabolic rate plus physical activity). BMR is the energy used just to keep the body alive at rest, and it changes with age, sex, body size and muscle. When intake matches output, weight is stable; a surplus is stored as fat and a deficit draws on stores. Almost every diet-and-health answer comes back to this equation.

Diet, disease and weight

Diet-related diseases shows the long-term cost of an unbalanced diet: obesity from a sustained energy surplus, coronary heart disease from too much saturated fat and salt, type 2 diabetes from obesity and excess sugar and refined carbohydrate, and high blood pressure from too much salt. The exam reward is to link the dietary cause to the mechanism (for example, saturated fat raising blood cholesterol which narrows the arteries) and then to the prevention.

Weight management applies energy balance to losing, gaining or maintaining weight, explains why crash diets fail (they cause muscle loss and rebound), and introduces body mass index (BMI = weight / height squared) as a screening tool with known limits.

Tailoring the diet to the person

Dietary needs across the life cycle explains how needs shift from childhood (growth, calcium, iron) through the teenage years (high energy, protein) and pregnancy (folate, iron, calcium) to older age (less energy, but still calcium, vitamin D and fibre).

Special dietary needs covers vegetarians and vegans (planning for protein, iron, vitamin B12 and calcium), diabetics (controlling sugar and refined carbohydrate), people with allergies and intolerances (avoiding the allergen while keeping the diet adequate), and cultural or religious diets such as halal and vegetarian Hindu diets. The skill assessed is adapting a meal safely without leaving it short of a nutrient.

How diet and health is examined

Apply energy balance. Section B gives intake and output figures and asks you to predict weight change or calculate a balance.
Explain disease with a mechanism. Section C asks how a diet causes a named disease; the marks are in the mechanism and the prevention, not just naming the food.
Justify nutrients for a group. Pregnancy, childhood and old age are favourite essay subjects; match the nutrient to the need and explain why.

Working out a person's energy balance

A 30-year-old office worker has a basal metabolic rate of 6000 kJ per day and uses 2500 kJ per day in activity. She eats 9500 kJ per day. Predict what will happen to her weight and advise her.

step Find her total energy output

Total energy output = BMR + activity = 6000 + 2500 = 8500 kJ per day. This is the energy she uses each day just to live and move.

step Compare intake with output

Energy intake = 9500 kJ. Output = 8500 kJ. Intake is greater than output by 9500 - 8500 = 1000 kJ per day, so she is in an energy surplus.

step Predict the effect on weight

A daily surplus of 1000 kJ is stored as body fat, so over weeks and months she will gain weight. If this continues for years it could lead to obesity and raise her risk of type 2 diabetes and heart disease.

step Advise a practical correction

To return to balance she should either reduce intake by about 1000 kJ a day (for example, swapping a sugary drink and a fried snack for water and fruit) or increase activity (a brisk daily walk), or a combination of both. Cutting saturated fat, sugar and salt while keeping protein and fibre lets her lose fat steadily without the muscle loss and rebound of a crash diet.

This module applies the nutrients to health. A balanced diet provides all nutrients in the right proportions with enough but not excess energy, shown in Singapore by My Healthy Plate. Energy balance compares energy in from food with energy out (basal metabolic rate plus activity): a surplus is stored as fat and a deficit draws on stores. A long-term unbalanced diet causes obesity, coronary heart disease, type 2 diabetes and high blood pressure, each prevented by less saturated fat, sugar and salt and more fibre, fruit and vegetables. Weight is managed through energy balance, with BMI (weight divided by height squared) as a screening tool. Needs change across the life cycle, and special groups such as vegetarians, diabetics, allergy sufferers and cultural or religious diets need meals adapted to stay safe and adequate.

Check your knowledge

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

State what is meant by a balanced diet. (2 marks)
Explain what happens to body weight when energy intake is consistently greater than energy output. (2 marks)
Explain how a diet high in saturated fat can lead to coronary heart disease. (3 marks)
Calculate the BMI of a person of mass 70 kg and height 1.75 m, and state how it is used. (3 marks)
State two nutrients a pregnant woman needs in greater amounts and explain why. (4 marks)

Solutions

Q1: A balanced diet provides all the nutrients the body needs (protein, carbohydrate, fat, vitamins, minerals, fibre and water) in the correct amounts and proportions, with enough energy to meet needs but not so much that it is stored as excess fat.
Q2: When intake is consistently greater than output the body is in an energy surplus. The extra energy is stored as body fat, so weight increases over time, and a prolonged surplus can lead to obesity.
Q3: A diet high in saturated fat raises the level of cholesterol in the blood. The cholesterol is deposited on the walls of the coronary arteries, narrowing them and reducing blood flow to the heart muscle. If an artery becomes blocked the heart muscle is starved of oxygen, causing a heart attack.
Q4: BMI = weight / (height x height) = 70 / (1.75 x 1.75) = 70 / 3.0625 = 22.9. This falls in the healthy-weight range, and BMI is used as a quick screening tool to classify whether a person is underweight, healthy, overweight or obese.
Q5: Any two with reasons: iron, to make extra haemoglobin for the increased blood volume and to build the baby's stores, preventing anaemia; calcium, to build the baby's bones and teeth without depleting the mother's; folate (folic acid), to reduce the risk of neural tube defects in the developing baby; protein, for the growth of the baby's tissues. (One nutrient plus one valid reason scores two marks each.)

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)