Most foods provide a mixture of nutrients; some foods contain a lot more calories than others. For example, foods that are watery or fibrous, such as apples or broccoli, contain fewer calories than foods which are fatty and greasy, such as crisps or chicken wings.

When you take in more calories than your body needs, the extra calories are stored as body fat or as glycogen, which is a storage form of carbohydrate.

What is protein?

Just about every part of your body is made up of protein: muscles, heart, lungs, bones, blood, nails and hair. Protein provides energy for your body and is needed to help you grow, build and repair cells in your body.

Proteins are made up of chains of building blocks called amino acids. There are 20 different kinds of amino acids which can be joined together in lots of different ways to make different proteins.

Some amino acids can be made by your body while others cannot; these essential amino acids have to be provided by the foods you eat. Some protein foods such as meat, fish, chicken, eggs, milk and cheese contain all the essential amino acids your body needs, while other protein foods such as nuts, rice, wheat, oats, soy beans and vegetables lack essential amino acids.

Although you can't get all the amino acids you need from eating rice or beans alone, if you have these foods together, you will get all the essential amino acids you need.

What are carbohydrates?

Carbohydrates are your body's main form of energy. There are two kinds of carbohydrates found in foods.

Simple carbohydrates include sugars which are found in white sugar, milk and boiled sweets. Your body can break down these simple carbohydrates quickly and easily.

Fibre and starchy foods are sources of complex carbohydrates. This type of carbohydrate takes longer to break down and gives you energy more slowly.

Complex carbohydrates are found in vegetables, potatoes, rice, pasta and bread. Fruit contains both simple and complex carbohydrates.

What is fat?

Fats are responsible for storing energy in your body. Fat reserves are used when carbohydrate energy is low.

You need fat for your body to work properly. For example, fats act as a cushion for your heart and lungs, they help to carry nutrients through your body and they protect your bones from injury. Your brain also needs fats to develop properly. The layer of fat under your skin helps to insulate you in the cold winter months.

However, fats are needed in smaller amounts than carbohydrates and protein.

Some foods, like most fruits and vegetables, have almost no fat while other foods have plenty of fat. These include nuts, oils, peanut butter, butter, beef, salmon, cookies and crisps.

There are different types of fats in foods, and some are healthier than others. Fats in plant foods and fish are good for your heart while the type of fats in snacks and fried foods, meat, and dairy products, such as butter, cheese and milk, can increase your chances of getting heart disease.