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Obesity - What is obesity?

BMJ Group Medical Reference


Obesity is very common in the UK. If someone is obese, they weigh much more than is healthy. Obesity can cause serious health problems, so it's important to see a doctor.

We've brought together the best research about obesity and looked carefully at the evidence about how to treat it. You can use our information to talk to your doctor and decide which treatments are best for you.

The information here is about obesity in adults. To find out more about helping children keep to a healthy weight, see Weight problems in children.

If you're obese, it means you weigh much more than is healthy for you. It happens because you eat more calories than your body uses. The extra calories are stored as fat.


Being obese is more than being just a few kilograms or pounds overweight. Obesity can cause health problems such as diabetes, high blood pressure, arthritis, and heart disease. And it makes some people feel bad about themselves.

To find out more, see How obesity affects your life.

Losing weight isn't easy. You'll need to change the way you eat and the amount of exercise you take. But if you make these changes, you'll be healthier.

The information here is about obesity in adults. To find out more about helping children keep to a healthy weight, see Weight problems in children.

Key points about obesity

  • Obesity is a serious medical condition.

  • Losing even a small amount of weight can lower the risk to your health.

  • Cutting down on calories, getting more exercise and learning good eating habits can help you lose weight.

  • Medical treatments may also help.

  • You're more likely to lose weight if you get help from a health professional. Most people start with their GP.

  • If you're very obese, surgery can help you lose a lot of weight. But there are risks with surgery so doctors usually only recommend it if your health is in danger.

What's a healthy weight?

When doctors talk about a 'healthy' or 'ideal' weight, they mean a weight that lowers your risk of getting serious health problems, such as heart disease or high blood pressure. It's not based on how thin you would like to look.[1]

Most doctors use the body mass index (BMI for short) to work out whether you're at a healthy weight. Your BMI is a single number that's worked out from your height and weight. You can work out your own BMI.

This table shows what the different BMI scores mean.[2][3]

BMI What it means
Less than 18.5 Underweight
18.5 to 24.9 Healthy weight
25 to 29.9 Overweight
30 or greater Obese

There are problems with using someone's BMI to find out if they're overweight.[4] For example, an athlete who's very muscular may have a BMI that suggests they're overweight, even though they're healthy. That's because muscle is heavier than fat. However, for most people, working out their BMI is a quick and simple way of finding whether their weight is healthy. To read more, see How do doctors diagnose obesity?

How your body uses food
1 | 2 | 3 | 4 | 5
Last Updated: June 21, 2012
This information does not replace medical advice.  If you are concerned you might have a medical problem please ask your Boots pharmacy team in your local Boots store, or see your doctor.
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