The eatwell plate

A balanced diet is a diet in which all the components needed to maintain health are present in appropriate proportions.

The eatwell plate shows the proportions of the different components that should be eaten daily in a well-balanced diet.

Food wheel showing healthy diet. Fresh fruit and vegetables should be largest part of diet, then carbohydrates, proteins and dairy products. Fats and sugars should be smallest part of the diet.

A balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre.

Energy requirements

The amount of energy we need varies. This is due to the following factors:

age
activity levels
pregnancy

Age

The amount of energy we need tends to increase as we approach adulthood.

Age in years	Daily energy requirement in kJ
0 (newborn)	2,000
2	5,000
6	7,500
13 (girl)	9,000
13 (boy)	11,000
16 (girl)	9,000
16 (boy)	12,000

Age in years	0 (newborn)
Daily energy requirement in kJ	2,000

Age in years	2
Daily energy requirement in kJ	5,000

Age in years	6
Daily energy requirement in kJ	7,500

Age in years	13 (girl)
Daily energy requirement in kJ	9,000

Age in years	13 (boy)
Daily energy requirement in kJ	11,000

Age in years	16 (girl)
Daily energy requirement in kJ	9,000

Age in years	16 (boy)
Daily energy requirement in kJ	12,000

Adult hand holding a young baby’s hand — Figure caption,
A baby needs much less energy than a teenager or an adult

The energy needs of adults go down as they age. For example, people in their 50s need about 17 per cent less energy in their diet than people in their 30s.

Activity levels

People who are active tend to need more energy than people. For example, an adult office worker might need 10,000 kJ per day, but a manual worker might need 15,000 kJ per day.

Pregnancy

In general, the greater a person’s , the more energy they need. Men tend to need more energy than women, and a woman’s energy needs increase when she is pregnant. This is mainly because she is carrying extra mass.

The energy content of food

The energy content in a food sample can be measured using simple .

To carry out this experiment, you need to:

pour 10 cm³ cold water into a boiling tube
record the starting temperature of the water
record the mass of the food sample
heat the food in a Bunsen flame until it catches fire
heat the water using the flame from the burning food
record the final temperature of the water

A test tube filled with water with a thermometer inside the tube. Burning food on a mounted needle is held below the tube. — Figure caption,
Investigating the energy content in a food sample

Calculations

To work out the energy per gram of food transferred to the water, use this equation.

\(\text{energy transferred (J) =}\)

\(~\frac{\text{mass of water (g)}\times 4.2~\text{J/g~}{^\circ\text{C}}\times\text{temperature increase~} {\text{(}{^\circ\text{C)}}}}{\text{mass of food (g)}}\)

Question

Two crisp breads are tested to see which provides the most energy per gram.

0.7 g of crisp bread A is burned and increases the temperature of 10 cm³ of water by 15°C.

0.5 g of crisp bread B is burned and increases the temperature of 10 cm³ of water by 20°C.

Using the equation, calculate the energy transferred from each sample. If the answer is more than 1,000 joules, you should express the answer in kilojoules: 1,000 J = 1 kJ.

Note that 1 cm³ of water has a mass of 1 g.

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The digestive system in humans – WJECThe eatwell plate