What is obesity?

  • Obese is a medical term used to describe a person with a high excess of body fat.

  • A person is obese if their body mass index (BMI) is greater than 30 kg/m².

  • An obese person is at greater risk of type-2 diabetes, heart disease and some types of cancer.

A school fitness adviser explains what obesity is and the methods we can take to avoid it

What is obesity?

A person is said to be obese if they have such a high excess of body fat that their health might be affected.

Health workers use body mass index (BMI) to assess obesity. They measure the height and mass of a person and then use the equation below to calculate their BMI:

BMI = mass (kg) ÷ height² (m²)

For example, if a person has a mass of 60 kg and a height of 1.65 m:

BMI = 60 kg ÷ 1.65²

BMI = 22 kg/m²

A person is overweight if their BMI is between 25 kg/m² and 30 kg/m². A person with a BMI over 30 kg/m² is said to be obese.

Therefore, the person in our example is not overweight or obese.

How does a person become obese?

A person becomes obese by eating food that supplies more energy than they need.

A 13-year old girl needs about 9,000 kilojoules (KJ) of energy each day. Boys the same age needs around 10,000 KJ/day. Adult women need roughly 8,400 KJ/day and adult men need roughly 10,500 KJ/day. If people consistently eat food that supplies more energy than this, without taking extra exercise, they might eventually become obese.

Health problems related to obesity

Obesity increases the risk of life-threatening health problems, including:

  • Heart disease
  • Stroke
  • Type-2 diabetes
  • Some types of cancer, including cancers of the breast, bowel and liver

A person can prevent obesity by eating sensible amounts of nutritious food and exercising regularly. Most obese people can lose weight by eating less and exercising more.

Obesity quiz

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