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Diet and digestion

Underweight, overweight

In warm weather, or when you are not doing much exercise, you do not need to eat as much food as when it is cold, or when you have exerted yourself physically. If you eat too much food without taking enough exercise, you will become overweight, with very overweight people being described as obese. Overweight people may suffer from health problems, including:

  • diabetes - an illness in which the body is unable to control the amount of sugar in the blood
  • arthritis - an illness in which the joints become worn, inflamed and painful
  • heart disease
  • breast cancer


Teenagers are growing quickly and need plenty of protein. But people in developing countries may not get enough protein in their diet. This is called protein deficiency. It can lead to a disease called kwashiorkor, which causes a swollen abdomen.

You can calculate the recommended daily average (RDA) intake of protein using this formula:

RDA in g = 0.75 × body mass in kg


What is the protein RDA for a person with a body mass of 60kg?

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RDA = 0.75 × 60 = 45g

Body Mass Index

The Body Mass Index (BMI) is a guide to whether someone is underweight, normal weight or overweight. You can calculate the BMI using this formula:

BMI = mass in kg ÷ (height in m)2


What is the BMI of a 1.7 metre-tall person with a body mass of 60kg?

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BMI = 60 ÷ (1.7)2 = 20.8

In this example, the person would be at the ideal weight for their height.

The meaning of BMI's

under 18.4underweight
between 18.5 and 24.9ideal weight
between 25 and 29.9over the ideal weight
between 30 and 39.9obese
over 40very obese

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