It's a common problem in the UK that's estimated to affect around 1 in every 4 adults and around 1 in every 5 children aged 10 to 11.
How to tell if you're obese
The most widely used method to check if you're a healthy weight is body mass index (BMI).
BMI is a measure of whether you're a healthy weight for your height. You can use the NHS BMI healthy weight calculator to work out your score.
For most adults, a BMI of:
18.5 to 24.9 means you're a healthy weight
25 to 29.9 means you're overweight
30 to 39.9 means you're obese
40 or above means you're severely obese
BMI is not used to diagnose obesity because people who are very muscular can have a high BMI without much fat.
But for most people, BMI is a useful indication of whether they're a healthy weight.
A better measure of excess fat is waist size, which can be used as an additional measure in people who are overweight (with a BMI of 25 to 29.9) or moderately obese (with a BMI of 30 to 34.9).
Generally, men with a waist size of 94cm or more and women with a waist size of 80cm or more are more likely to develop obesity-related health problems.
Risks of obesity
It's very important to take steps to tackle obesity because, as well as causing obvious physical changes, it can lead to a number of serious and potentially life-threatening conditions.
Obesity can also affect your quality of life and lead to psychological problems, such as depression and low self-esteem.
The best way to treat obesity is to eat a healthy reduced-calorie diet and exercise regularly.
To do this, you should:
eat a balanced calorie-controlled diet as recommended by a GP or weight loss management health professional (such as a dietitian)
join a local weight loss group
eat slowly and avoid situations where you know you could be tempted to overeat
You may also benefit from receiving psychological support from a trained healthcare professional to help change the way you think about food and eating.
If lifestyle changes alone do not help you lose weight, a medicine called orlistat may be recommended.
If taken correctly, this medicine works by reducing the amount of fat you absorb during digestion. Your GP will know whether orlistat is suitable for you.