Fat as a macronutrient: its function in the body, saturated and unsaturated fats, fatty acids, cholesterol, food sources, and the effects of too much or too little fat.

What this dot point is asking

You need to know what fat does in the body, the difference between saturated and unsaturated fat, what fatty acids and cholesterol are, the main food sources, and the effects of eating too much or too little.

The function of fat

Fat is a macronutrient. Its roles are:

• the most concentrated source of energy (about 9 kcal per gram, more than twice carbohydrate or protein),
• carrying and helping absorb the fat-soluble vitamins A, D, E and K,
• providing essential fatty acids the body cannot make,
• insulating the body to keep it warm,
• protecting organs such as the kidneys,
• adding flavour and a feeling of fullness.

Saturated and unsaturated fats

Fats are made of fatty acids, which are described as saturated or unsaturated.

• Saturated fats: usually solid at room temperature, mainly from animal sources (butter, lard, fatty meat, full-fat dairy) and some processed foods. Too much raises blood cholesterol and the risk of heart disease.
• Unsaturated fats: usually liquid at room temperature, mainly from plant sources (olive, sunflower and rapeseed oils) and oily fish; these are the healthier choice and include the omega-3 fats in oily fish.

The advice is to swap saturated fats for unsaturated fats.

Cholesterol

Food sources

• High in saturated fat: butter, lard, cream, cheese, fatty meat, pastry, cakes and biscuits.
• High in unsaturated fat: vegetable oils, nuts, seeds, avocado and oily fish.

Much of the fat we eat is hidden in processed foods such as pastries, cakes, biscuits, crisps and ready meals, so reading the nutrition label helps you compare products and choose lower-fat options. Labels often show fat split into total fat and "of which saturates", and traffic-light colours flag foods that are high (red), medium (amber) or low (green) in fat.

Government advice (the Eatwell Guide) is to eat fatty and sugary foods less often and in small amounts, to grill, bake or steam rather than fry, and to choose unsaturated oils and spreads. Cutting visible fat from meat and choosing lower-fat dairy are simple swaps that reduce saturated fat without losing other nutrients.

The effects of too much or too little fat

Too much fat:

• it is energy-dense, so excess leads to weight gain and obesity,
• too much saturated fat raises cholesterol and the risk of heart disease.

Too little fat:

• not enough fat-soluble vitamins (A, D, E, K) are absorbed,
• a lack of essential fatty acids,
• the body has less energy store, insulation and protection.