Nutrition and Food Groups
Introduction
Every living thing needs food, but food is only useful once the body can extract what it contains: energy and the raw materials for growth, repair, and everyday function. Nutrition is the study of these substances — called nutrients — and how the body uses them. A working knowledge of nutrition helps explain why a "balanced diet" is more than a slogan: each nutrient plays a distinct role, and missing one causes specific, predictable problems.
Macronutrients
Macronutrients are needed in relatively large amounts because they supply energy or bulk building material.
- Carbohydrates — the body's preferred energy source. Found in bread, rice, pasta, potatoes, and fruit. Digested into simple sugars such as glucose, which cells use for respiration.
- Proteins — used for growth, repair, and making enzymes and hormones. Found in meat, fish, eggs, beans, and dairy. Digested into amino acids, the building blocks the body reassembles into its own proteins.
- Fats — the most concentrated energy store, also used to insulate the body and cushion organs. Found in oils, butter, nuts, and oily fish. Digested into fatty acids and glycerol.
Each gram of carbohydrate or protein releases about 4 kilocalories of energy; each gram of fat releases about 9 kilocalories, which is why fatty foods are far more energy-dense.
Micronutrients
Micronutrients are needed only in small amounts, but a shortage still causes real harm because they enable processes that macronutrients cannot carry out alone.
- Vitamins — organic compounds the body mostly cannot make itself. Vitamin A supports vision, vitamin C supports the immune system and wound healing, vitamin D supports calcium absorption for bone growth, and the B vitamins support energy release from food.
- Minerals — inorganic elements needed for specific jobs. Calcium builds bones and teeth, iron is a component of haemoglobin (needed to carry oxygen in blood), and iodine is needed to make thyroid hormone.
Water and Fibre
Water is not a food in the usual sense, but it is essential: it makes up most of the body's mass, transports nutrients, and regulates temperature through sweating. Fibre (found in whole grains, fruit, and vegetables) is not digested at all, but it adds bulk to waste, helps the gut muscles move food along, and supports a healthy population of gut bacteria.
The Main Food Groups
Balanced-diet models typically group foods by their main nutrient contribution:
| Food group | Main nutrient supplied | Examples |
|---|---|---|
| Grains and starchy foods | Carbohydrates | Bread, rice, pasta, potatoes |
| Protein foods | Protein | Meat, fish, eggs, beans, lentils |
| Dairy and alternatives | Protein, calcium | Milk, cheese, yoghurt, fortified plant milks |
| Fruit and vegetables | Vitamins, minerals, fibre | Apples, carrots, spinach, oranges |
| Fats and sugars | Concentrated energy | Oils, butter, sweets, fried food |
A balanced diet draws mostly from the first four groups, with fats and sugars eaten sparingly since they are easy to over-consume.
Malnutrition
Malnutrition means a diet that does not meet the body's needs, and it covers both too little and too much:
- Undernutrition — insufficient calories or nutrients, leading to weight loss, stunted growth in children, and weakened immunity.
- Deficiency diseases — caused by a lack of a specific micronutrient, for example scurvy (vitamin C), rickets (vitamin D), anaemia (iron), and goitre (iodine).
- Overnutrition — excess calories, especially from fat and sugar, linked to obesity, type 2 diabetes, and heart disease.
Key Terms
| Term | Definition |
|---|---|
| Nutrient | A substance in food that the body uses for energy, growth, or repair |
| Macronutrient | A nutrient needed in large amounts: carbohydrate, protein, or fat |
| Micronutrient | A nutrient needed in small amounts: a vitamin or mineral |
| Balanced diet | A diet supplying the right proportions of all nutrient groups |
| Malnutrition | A diet that provides too little or too much of one or more nutrients |
| Deficiency disease | An illness caused by a long-term lack of a specific nutrient |
Worked Example
Q: Explain why a diet of only bread and rice, with no fruit, vegetables, or dairy, would eventually cause health problems even if it provided enough calories.
Bread and rice supply carbohydrates and some protein, so the body would have enough energy. However, this diet supplies almost no vitamin C, vitamin A, calcium, or iron, since these come mainly from fruit, vegetables, and dairy. Over time, the person would develop deficiency diseases such as scurvy (from lack of vitamin C) and weak bones (from lack of calcium), even though they were not short of energy. This shows that enough calories is not the same as good nutrition — the diet also has to supply the full range of micronutrients.
Common Mistakes
- Assuming "enough food" means "enough nutrition" — calories and nutrient variety are separate requirements.
- Confusing macronutrients and micronutrients — the "macro/micro" split refers to the amount needed, not how important the nutrient is.
- Thinking fat should be avoided entirely — the body needs some fat for cell structure, insulation, and absorbing certain vitamins; the concern is usually excess, not presence.
- Forgetting fibre and water are not "nutrients" in the energy sense, but are still essential to a healthy diet.
Tips and Tricks
- Remember the energy values: carbohydrate and protein ≈ 4 kcal/g, fat ≈ 9 kcal/g — more than double.
- Link each deficiency disease to its missing micronutrient: Scurvy → Vitamin C, Rickets → Vitamin D, iodine → goitre, iron → anaemia.
- A simple way to check a meal is balanced: does it include a starchy food, a protein food, and at least one fruit or vegetable?
- "Protective foods" (fruit and vegetables) is a useful phrase for remembering that vitamins and minerals primarily protect against illness rather than supply energy.