What is protein, where do we get it, and why does the body need it?
Protein as a macronutrient, its sources, functions and structure, high and low biological value protein, protein complementation, and the effects of too much or too little protein.
A focused CCEA GCSE Food and Nutrition answer on protein, covering its functions, animal and plant sources, high and low biological value protein, protein complementation, and the effects of deficiency and excess.
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What this dot point is asking
CCEA wants you to know what protein is, where it comes from, what the body uses it for, the difference between high and low biological value protein, how protein complementation works, and what happens if you eat too much or too little.
What protein is
Because the body cannot store spare protein, a steady supply is needed every day. Protein is described as a macronutrient because it is needed in fairly large amounts, unlike vitamins and minerals.
Functions of protein
Growth matters most during childhood, adolescence and pregnancy, when the body is building new tissue quickly. Repair goes on all the time as old cells are replaced and wounds heal.
High and low biological value protein
The biological value of a protein describes how many of the essential amino acids it contains.
| Type | Contains | Main sources |
|---|---|---|
| High biological value (HBV) | All essential amino acids | Meat, fish, eggs, milk, cheese, soya |
| Low biological value (LBV) | Missing one or more essential amino acids | Beans, lentils, peas, nuts, cereals, bread |
Most animal foods are HBV. The important exception to learn is soya, a plant food that is HBV, which is why soya products such as tofu are useful for vegetarians and vegans.
Protein complementation
This is the key idea for anyone who eats little or no animal protein. Classic combinations are beans on toast (pulse plus cereal), rice and dahl (cereal plus pulse), and hummus with pitta (pulse plus cereal).
Too much and too little protein
Eating too little protein, especially in growing children, leads to poor growth, slow wound healing, weak muscles and a weakened immune system. Severe long-term deficiency causes the condition kwashiorkor.
Eating too much protein is converted to fat and stored, contributing to weight gain, and the extra waste products place a strain on the kidneys and liver.
Examples in context
- Example 1. Why pregnant women need more protein
- During pregnancy the mother is building the tissues of a growing baby as well as her own placenta and blood supply, so her protein requirement rises. CCEA links this directly to protein's role in growth, which is why life-stage questions reward naming extra protein for pregnancy and explaining it in terms of building new tissue.
- Example 2. The cost angle on protein choice
- HBV animal protein such as steak or fresh fish is often expensive, while LBV plant proteins such as dried lentils and beans are cheap and store well. A family on a tight budget can meet its protein needs by using complementation, for example a lentil and rice dish, instead of meat. This is a good link to factors affecting food choice, where economic factors shape what people buy.
- Example 3. Protein in a sportsperson's diet
- An athlete training to build muscle needs plenty of protein for repair and growth of muscle tissue after exercise. They might add eggs, chicken or a milk-based drink after training. The point CCEA looks for is matching the function of protein (growth and repair) to the increased need of that group.
Try this
Q1. Name two high biological value protein foods that are suitable for a vegetarian. [2 marks]
- Cue. Eggs, milk, cheese or soya (any two).
Q2. State two effects of eating too little protein. [2 marks]
- Cue. Poor growth and slow wound healing (also weak muscles, weak immunity).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA past-style6 marksExplain the difference between high biological value and low biological value protein, and describe how a vegan can still get all the essential amino acids they need.Show worked answer →
Six marks: definitions plus the idea of complementation with examples.
High biological value (HBV) protein contains all the essential amino acids the body cannot make. It comes mainly from animal foods such as meat, fish, eggs, milk and cheese, plus the plant food soya.
Low biological value (LBV) protein is missing one or more essential amino acids. It comes from most plant foods such as beans, lentils, peas, nuts, cereals and bread.
A vegan eats no animal protein, so they rely on plant sources. By combining two different LBV foods in one meal, the amino acid missing from one is supplied by the other. This is protein complementation. Good examples are beans on toast (pulses plus cereal) or rice and dahl (cereal plus pulses).
Markers reward correct definitions, the term complementation, and at least one valid plant-food combination.
CCEA past-style4 marksDescribe four functions of protein in the body.Show worked answer →
Four marks, one for each function.
Protein is needed for the growth of new body cells and tissues, which is why children, teenagers and pregnant women need extra.
It is needed for the repair and maintenance of body tissues, such as healing wounds and replacing worn-out cells.
It is used to make enzymes, hormones and antibodies that keep the body working and fight infection.
It can be used as a secondary source of energy when carbohydrate and fat intake is too low.
Markers accept any four correct functions.
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