3.4 Unhealthy diet

Summary: You may have seen pictures of people who are either extremely overweight or underweight. Both of these conditions can be caused by malnourishment. These people may have eaten the wrong amount or the… Tags: science oxford-science student-book-7 biology Created: 2026-05-19 Last Updated: 2026-05-19

After this topic, you will be able to:

• describe some health issues caused by an unhealthy diet
• state the meaning of a vitamin or mineral deficiency
• compare the Energy requirements of different people.

Think back

1. Give one problem that may be caused by eating an unhealthy diet.
2. Name the two types of nutrient that provide the body with energy.
3. Name a good source of vitamins and minerals.

Key idea An unhealthy diet can cause health issues. Some health issues include being underweight, being overweight, and not having enough vitamins or minerals in your diet. This is called a deficiency.

Key words malnourishment, starvation, obese, deficiency

You may have seen pictures of people who are either extremely overweight or underweight. Both of these conditions can be caused by malnourishment. These people may have eaten the wrong amount or the wrong types of food. An unhealthy diet can cause health issues.

Where does your energy come from?

You need energy for everything you do, even to sleep. This energy comes from your food. You can see how different types of food make up a balanced diet in Figure 1. The largest part of your diet should be carbohydrates. You should only eat lipids, oils, and sweets in very small quantities.

Figure 1This food pyramid shows a healthy balanced diet. Full text alternative to the content

The energy in food is measured in joules (J) or kilojoules (kJ). 1 kilojoule is the same as 1000 joules. A food label will tell you how much energy is stored in that food.

A Write down the number of joules in 2 kJ.

Why is it unhealthy to be underweight?

Some people do not eat enough food. In extreme cases, this is called starvation. If the energy in the food you eat is less than the energy you use, you will lose body mass and become underweight. Underweight people:

• often suffer from health problems, such as a weak immune system
• do not have energy to do things, and are often tired
• are likely to suffer from a lack of vitamins or minerals.

B State three problems caused by being underweight.

Why is it unhealthy to be overweight?

Some people eat too much, or eat too many fatty foods. If the energy in the food you eat is more than the energy you use, you increase your body mass. This is stored as fat under the skin. If a person becomes extremely overweight, they are obese. Overweight people have a greater risk of:

• heart disease
• stroke
• diabetes
• some cancer

C State three diseases that obese people are more likely to suffer from.

What are vitamin and mineral deficiencies?

If a person does not have enough of a particular vitamin or mineral, they have a deficiency. This can damage their health. For example, a vitamin A deficiency can lead to ‘night blindness’. This makes it difficult for you to see clearly in low levels of Light. A vitamin D deficiency can cause a condition called rickets, where your bones become weak (see Figure 2).

Figure 2This person is suffering from rickets.

How much energy do you need?

Your body needs energy to function properly. The amount of energy you need depends on your age (as this affects your growth rate), your body size, and how active you are. The more exercise you do, the more energy your body requires. The graph in Figure 3 shows how different people require different amounts of energy.

Figure 3Daily energy requirements for different types of people. Full text alternative to the content

D Identify which of these people needs more energy to do their job: a farmer, a computer programmer, a librarian.

Maths skills To calculate percentage change: Calculate the percentage change for the energy requirements of a female office worker who becomes pregnant. Use the graph in Figure 3.

Stretch zone

1. Copy and complete the sentences. You gain the balance/energy you need to survive from food. Energy is measured in joules/grams. If you take in more energy than you need, you can become overweight/underweight. This increases the risk of diseases such as diabetes/rickets. An underweight person is often full of energy/tired.
2. Use the graph in Figure 3 to answer the questions. Calculate the amount of extra energy a female office worker would need each day if she became pregnant.A male office worker starts a new job as a construction worker. Calculate the percentage increase in his daily energy needs.

Stretch zone

1. Use the graph in Figure 3 to estimate the daily energy requirements of a female science teacher. Give reasons for your answer.