What Is Nutrition?
Nutrition is about understanding the chemical substances found in food — called nutrients — and how the body uses them. A good diet provides all the nutrients your body needs in the right amounts. Eating well keeps your body working properly, helps you grow, gives you energy, and protects you from disease.
Nutrients are divided into two broad groups: macronutrients (needed in large amounts) and micronutrients (needed in smaller amounts but still essential).
Macronutrients
Carbohydrates are the body's main source of energy. Sugars (like glucose and fructose) are simple carbohydrates that are digested and absorbed quickly. Starches (found in bread, rice, potatoes, and pasta) are complex carbohydrates that provide a slower, steadier release of energy. Fibre is a special type of carbohydrate that the body cannot fully digest, but it keeps the digestive system healthy and helps prevent constipation.
Proteins are essential for growth and repair. They are made of smaller units called amino acids. Your body uses proteins to build and repair muscles, make enzymes and hormones, and support the immune system. Good sources include meat, fish, eggs, dairy, beans, and lentils.
Fats are a concentrated energy source and are essential for making cell membranes, absorbing fat-soluble vitamins, and insulating the body. There are two main types: saturated fats (mainly from animal products — should be eaten in moderation) and unsaturated fats (from plant oils, nuts, and fish — healthier option).
Water is often forgotten as an essential nutrient, but it is the most important of all! Your body is about 60% water. Water is needed for almost every chemical reaction in the body, for digestion, for removing waste, and for regulating body temperature. You should drink around 6–8 glasses of water per day.
Micronutrients: Vitamins and Minerals
Vitamins are organic compounds needed in tiny amounts for specific body functions. For example, Vitamin C (found in citrus fruits) is needed for healthy skin and wound healing. Vitamin D (made by skin in sunlight, also in fatty fish) helps the body absorb calcium for strong bones. Vitamin A (in carrots, liver) is important for vision.
Minerals are inorganic elements also needed in small amounts. Calcium (in dairy, leafy greens) is crucial for strong bones and teeth. Iron (in red meat, spinach) is needed to make haemoglobin in red blood cells. Potassium (in bananas, potatoes) helps maintain healthy blood pressure and nerve function.
A Balanced Diet
A balanced diet provides all nutrients in the right proportions. The Eatwell Plate (or similar guides in different countries) recommends that meals should contain plenty of fruits and vegetables (at least five portions a day), a good portion of starchy carbohydrates, moderate amounts of protein, some dairy or dairy alternatives, and only small amounts of fats and sugars.
When thinking about a balanced meal, try to include at least three different food colours on your plate. Different coloured fruits and vegetables contain different vitamins and minerals — eating a "rainbow" helps ensure you get a wide variety of micronutrients.
Too much of any nutrient can be harmful, not just too little. A diet too high in saturated fat can lead to heart disease. Too much sugar contributes to tooth decay and obesity. Even too much of certain vitamins (like vitamin A) can be toxic. Balance is key.
Real world: reading a food label
A cereal box lists per 100 g: carbohydrates 72 g, protein 8 g, fat 3 g, fibre 5 g. A nutritionist uses these figures to assess whether the product provides balanced macronutrients. High sugar content (a simple carbohydrate) versus high fibre influences how quickly blood glucose rises after eating. Understanding nutrition labels is a practical life skill for managing diet and health.
Real world: iron deficiency anaemia
Iron is needed to produce haemoglobin in red blood cells. A teenager who eats little red meat or leafy greens may develop iron deficiency anaemia — feeling tired and breathless because red blood cells carry less oxygen. A GP prescribes iron supplements and dietary advice. This is a direct application of micronutrient knowledge to clinical practice.
Real world: vitamin D and sunscreen
In northern countries with low winter sunlight, people often develop Vitamin D deficiency because the skin cannot synthesise enough. Vitamin D is needed for calcium absorption — deficiency in children causes rickets (soft bones). Public health campaigns recommend Vitamin D supplements in winter and fortified foods — applied nutritional science.
Practice Problems
Name the three macronutrients and give one function of each.
Show answer
Why is Vitamin D important, and how can the body obtain it?