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Obesity - Introduction

NHS Choices Medical Reference

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Obesity is a term used to describe somebody who is very overweight with a high degree of body fat.

There are a number of ways a person's weight can be assessed. The most widely used method is body mass index.

Body mass index (BMI) is your weight in kilograms divided by your height in metres squared. You can use the NHS Choices BMI healthy weight calculator to work out your own BMI:

  • if your BMI is between 25 and 29, you would be considered overweight
  • if your BMI is between 30 and 40, you would be considered obese
  • if your BMI is over 40, you would be considered very obese (known as "morbidly obese")

Another useful method is to measure around your waist. People with very fat waists (94cm or more in men and 80cm or more in women) are more likely to develop obesity-related health problems.

The risks of obesity

Being obese increases your risk of developing a number of serious and potentially life-threatening diseases, such as:

In addition, obesity can damage your quality of life and can often trigger depression.

Read more about the complications of obesity.

Obesity in children

Obesity is also an increasing problem in children, with around one in seven children classified as obese.

Read advice for parents of obese children.

Obesity and pregnancy

If you're pregnant, being very overweight can cause complications for you and your baby.

Find out more about obesity and pregnancy.

Treatment of obesity

There are four main goals in the treatment of obesity:

  • preventing further weight gain
  • gradually losing weight through a combination of a calorie-controlled diet and regular exercise
  • avoiding regaining any lost weight
  • improving general health and reducing the risk of obesity-related complications

Some people prefer a one-to-one consultation with a trainer or dietitian, while others prefer being part of a weight loss group, which can either be organised by local clinical commissioning groups (CCGs) or through commercial organisations. You may want to use an internet application such as the NHS BMI Tracker tool to monitor your weight.

A medication called orlistat can aid weight loss, but this should be used in combination with the steps mentioned above, not as an alternative. Your GP will be able to advise whether orlistat is suitable for you.

Many people will also need help examining and changing unhealthy patterns of thinking and behaviour.

Read more about the treatment of obesity.

Weight loss surgery

Weight loss surgery is used as a last resort to treat people who are dangerously obese. A gastric band or gastric bypass operation is only available on the NHS to treat people with potentially life-threatening obesity that does not respond to non-surgical treatments, such as lifestyle changes.

Read more about weight loss surgery for obesity.

Causes of obesity

Most cases of obesity are caused by a person eating more calories than they burn off, and the unused calories being turned into fat. Modern lifestyles also do not help:

  • there is easy access to cheap, high energy food that is often marketed aggressively 
  • people's lifestyles and jobs are much less active than in the past - many leisure activities, such as watching television, playing video games and browsing the internet, are usually done sitting down
  • people drive or use public transport and tend to walk a lot less than they used to

There are also a number of conditions that can cause weight gain, such as polycystic ovary syndrome.

Read more about the causes of obesity.

How many people are obese?

A survey published in 2012 found that just over a quarter of all adults (26%) in England are obese.

Outlook for obesity

There is no "magic wand" treatment for obesity. Weight loss programmes take commitment and can be challenging, but they are successful for people who stick with them.

Research looking at obese people who completed a commercial weight loss programme lasting 12 months found they lost around 5-10% of their body weight.

While this may not sound like a great amount, it is important to stress that even a modest reduction in weight brings important health benefits. Losing this amount of weight will significantly reduce your risk of developing conditions such as type 2 diabetes and heart disease.

Medical Review: March 05, 2012
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