What makes up a balanced diet, and how do we test food for the main nutrients?
The components of a balanced diet and their sources and functions, the consequences of an unbalanced diet, the energy content of food, and the chemical food tests for starch, reducing sugar, protein and fat.
A focused CCEA GCSE Biology answer on nutrition, covering the components of a balanced diet and their functions, the effects of an unbalanced diet, energy content of food, and the food tests for starch, reducing sugar, protein and fat.
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What this dot point is asking
CCEA wants you to know the seven components of a balanced diet with their sources and functions, the problems caused by eating too much or too little, how energy content of food is measured, and the chemical food tests for starch, reducing sugar, protein and fat.
The components of a balanced diet
An unbalanced diet
Eating too much energy-rich food (fats and sugars) without exercise causes obesity, raising the risk of heart disease and type 2 diabetes. Eating too little of a nutrient causes a deficiency disease: too little vitamin C causes scurvy, too little iron causes anaemia, and too little energy overall causes starvation.
Energy content of food
The energy in food can be measured by calorimetry: a known mass of food is burned and used to heat a known volume of water. The temperature rise of the water shows how much energy was released.
Food tests
| Nutrient | Reagent | Positive result |
|---|---|---|
| Starch | Iodine solution | Orange-brown to blue-black |
| Reducing sugar | Benedict's solution, heated | Blue to brick-red precipitate |
| Protein | Biuret reagent | Blue to purple or lilac |
| Fat | Ethanol then water | Cloudy white emulsion |
Examples in context
- Example 1. Checking a baby milk formula
- A manufacturer must show a milk formula contains protein and fat for a growing baby. A biuret test turning the sample purple confirms protein, and shaking the sample with ethanol then adding water to give a milky emulsion confirms fat. By running all four tests, they build a profile of the food, which is exactly the skill CCEA assesses in food-test questions.
- Example 2. Why fibre matters even though it is not digested
- Fibre is the indigestible part of plant cell walls (cellulose). It is not broken down or absorbed, so it provides no nutrients, yet it is essential: it adds bulk that the muscles of the gut push against, keeping food moving and preventing constipation. This is a good example of a dietary component that helps health without being a source of energy or building material.
- Example 3. Reading an energy-content experiment
- A student burns a peanut under a boiling tube holding 20 cm cubed of water and records the temperature rise. A peanut, which is rich in fat, raises the water temperature much more than the same mass of a cracker, which is mostly starch. This makes sense because fat stores more energy per gram than carbohydrate. The investigation is not perfectly accurate, because heat is lost to the surroundings and not all the food burns, so the measured energy is always lower than the true value. Recognising these sources of error, and suggesting improvements such as a screen to reduce heat loss, is exactly the kind of evaluation CCEA rewards in data and practical questions.
Try this
Q1. Name the reagent used to test for protein and the colour change for a positive result. [2 marks]
- Cue. Biuret reagent; blue to purple.
Q2. State the function of fibre in the diet. [1 mark]
- Cue. It adds bulk to keep food moving through the gut and prevents constipation.
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 20204 marksDescribe the food tests you would use to show that a sample contains both starch and protein.Show worked answer →
Four marks for two complete tests, each with reagent, method and positive result.
Test for starch: add a few drops of iodine solution to the sample. If starch is present, the orange-brown iodine turns blue-black.
Test for protein: add biuret reagent (sodium hydroxide then a few drops of copper sulfate solution). If protein is present, the blue solution turns purple or lilac.
A sample containing both will turn blue-black with iodine and purple with biuret in separate tests.
Markers reward the correct reagent and the correct colour change for each test. No heating is needed for these two.
CCEA 20183 marksExplain two health problems that can result from an unbalanced diet.Show worked answer →
Three marks: name the problems and explain the cause.
Eating too much energy-rich food (fats and sugars) without enough exercise leads to obesity, because the excess energy is stored as fat. Obesity raises the risk of type 2 diabetes and heart disease.
Eating too little of a nutrient causes a deficiency. For example, too little vitamin C causes scurvy (bleeding gums), and too little iron causes anaemia (too few red blood cells, causing tiredness).
Eating too little energy overall leads to starvation and weight loss.
Markers reward a named problem linked to its dietary cause, for any two valid examples.
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Sources & how we know this
- CCEA GCSE Biology specification — CCEA (2017)