Macronutrients: Protein (AQA GCSE Food Preparation & Nutrition)

Macronutrients: protein

• Proteins are made up of long chains of amino acids held together by chemical bonds

  • Amino acid chains then fold to form proteins with specific structures and functions

Protein diagram

• Proteins have a range of functions in the body, including:

  • cell growth and cell division

  • repair and maintenance of tissues

  • an energy reserve; proteins can be broken down to release energy when the body has used up other energy stores

  • enzymes, antibodies and hormones

Sources of protein

• Protein-rich foods include:

  • meat

  • fish/seafood

  • dairy products

  • eggs

  • some grains, e.g. quinoa

  • Quorn

  • soya products

• Foods that contain protein in lower quantities include:

  • some cereal products, e.g. wheat, rice, oats, bread and pasta

  • nuts, e.g. peanut butter and almonds

  • seeds, e.g. sunflower seeds

  • some vegetables, e.g. corn, peas, beans and lentils

Protein deficiency and excess

• Protein is an essential component of a healthy diet, and a diet that contains either too little or too much protein can cause health problems

• Protein deficiency can result in problems such as:

  • reduced growth

  • brittle hair and nails

  • weakened immune system

  • poor digestion

  • a condition called kwashiorkor, which has symptoms such as swelling of the feet, hands, abdomen and face, as well as an enlarged liver

• A diet that contains an excess of protein can result in:

  • digestive issues and nausea

  • dehydration

  • headaches

  • damage to the kidneys and liver

  • cardiovascular disease

Dietary reference values for protein

• Dietary reference values provide an estimate of the amount of protein that is needed per day by people in different population groups

  • E.g. the average adult male should consume around 55 g per day and the average adult female needs around 45 g per day

• Dietary reference values differ between groups because, e.g.:

  • growing children need a lot of protein

  • active individuals are likely to need more protein to maintain muscle

  • pregnancy and breastfeeding increases the demand for protein

Data taken from a 1991 UK government Department of Health report

Low and high biological value proteins

• Amino acids can be described as essential or non-essential:

  • Essential amino acids can only be gained by consuming foods that contain these amino acids

  • Non-essential amino acids can be made by the body from other amino acids

• A healthy diet must include all essential amino acids in order for the body to function correctly

• High biological value (HBV) proteins contain all the essential amino acids

  • These are found in foods such as meat, fish and eggs, as well as soya products and quinoa

• Low biological value (LBV) proteins contain some but not all essential amino acids

  • These are found in foods like beans, nuts and pulses

• Protein complementation involves combining different LBV protein foods in order to gain all essential amino acids

  • E.g. beans on toast combines the LBV wheat proteins in bread with LBV plant proteins in beans, creating a meal that has a high biological value

  • This can be particularly useful for vegetarian or vegan diets which contain fewer HBV proteins

F7wiki, via Wikimedia Commons

Protein alternatives

• People with restricted diets, e.g. vegetarians and vegans, need to be especially careful to ensure that they gain enough dietary protein

• Protein alternatives can be consumed to provide protein that is not sourced from an animal

• Protein alternatives can include:

  • soya products that are made using the bean of the soya plant

    • Soya beans contain HBV proteins

    • The beans can be processed to produce a range of products, e.g. soya milk, miso and tofu

  • tofu that is made by causing the proteins in soya milk to coagulate, producing a solid curd

    • Tofu can be soft or firm

    • Adding tofu to stir fries and curries can increase the protein content of a meal

  • textured vegetable protein (TVP) that is mostly made from soya protein but can also contain other ingredients like wheat and oats

    • TVP can be processed to produce a similar texture to meat products so it is often used in vegetarian versions of meat-based dishes, such as burgers or bolognese sauce

  • mycoprotein that is produced from fungi grown in large vats before being processed into food

    • Quorn is a popular brand that produces vegetarian meat-like products using mycoprotein