Macronutrients: Fats (AQA GCSE Food Preparation & Nutrition)

Macronutrients: fats

• Fats can be present in food in the form of solid fats and liquid oils

• Fats have a range of functions in the body, such as:

  • a concentrated energy store

  • production of cell membranes

  • insulating the body to reduce heat loss

  • protecting internal organs against impact damage

  • allowing the absorption of fat soluble vitamins, e.g. A and D

Sources of fats

• Sources of animal fats include:

  • meat, e.g. bacon and pork belly contain visible fat

  • dairy, e.g. butter and cheese

  • fish

  • eggs

• Sources of plant fats include:

  • plant oils, e.g. olive oil and sunflower oil

  • avocados

  • olives

  • nuts and seeds

Fat deficiency and excess

• Fats are an essential dietary component, but must be consumed in the correct quantities to avoid deficiency or excess

• Fat deficiency can result in symptoms such as:

  • the body breaking down protein in order to release energy, which can lead to muscle loss and physical weakness

  • an inability to absorb fat-soluble vitamins, such as A, D, and E, resulting in vitamin deficiencies

  • omega-3 deficiency increases the risk of heart disease

  • increased heat loss

• An excess of dietary fat can also have negative consequences, such as:

  • weight gain and obesity

    • Obesity increases the risk of other associated conditions, such as type 2 diabetes

  • an increased risk of cardiovascular disease, e.g. high blood pressure, coronary heart disease and stroke

Dietary reference values for fats

• The dietary reference values for fats state that they should not supply more than 35 % of the energy we get from our food

  • The rest should come from other sources like carbohydrates

• The average adult should consume around 70 g of fat per day

  • No more than 20 g of this should come from saturated fat (see below)

Saturated and unsaturated fats

• Fat molecules in food are made up of three fatty acid chains and a single molecule of glycerol

Fat structure diagram

• The structure of the fatty acid chains affects the properties of fats

  • Fatty acid chains are hydrocarbons, made up of carbon atoms joined together with hydrogen atoms

• Fatty acid chains can either be saturated or unsaturated:

  • Saturated fatty acids contain no double bonds between carbon atoms

    • They are 'full up', or saturated, with hydrogen atoms

    • Saturated fats are more likely to be solid at room temperature, e.g. in:

      • meat

      • butter

      • lard

      • coconut oil

  • Unsaturated fatty acids contain at least one double bond between carbon atoms

    • They are not full up with hydrogen atoms

    • These fats are more likely to be liquid at room temperature, e.g. in:

      • plant oils, e.g. olive oil, rapeseed oil, sunflower oil

      • oily fish, e.g. salmon

    • Monounsaturated fatty acids contain a single double bond, e.g. avocado and peanut oil

    • Polyunsaturated fatty acids contain more than one double bond, e.g. soybeans and sunflower oil

Saturated and unsaturated fatty acids diagram

• Saturated fats are associated with increased blood cholesterol and are thought to increase the risk of heart disease

• Increasing the ratio of unsaturated fats to saturated fats in the diet is thought to reduce the risk of heart disease

  • Unsaturated fats are sometimes referred to as 'good fats' for this reason