Obesity - How do doctors diagnose obesity?
BMJ Group Medical Reference
To find out if you are obese, your doctor will probably work out your body mass index (BMI for short) and may take your waist and hip measurements. These figures can help him or her decide whether your weight is likely to seriously affect your health. Your GP will also ask about your general health and any other conditions you have.
To read more about what to expect, see Questions your doctor may ask.
Most doctors will work out your BMI. It tells the doctor whether your weight is healthy. It's worked out according to both your height and weight.
Your doctor will weigh and measure you. These numbers go into a mathematical formula that gives a single number. This is your BMI. You can work out your own BMI. This table shows what different BMI scores mean.
||What it means
|Less than 18.5
|18.5 to 24.9
|25 to 29.9
|30 or greater
Working out someone's BMI isn't a perfect way of telling if they are overweight. 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.
A study comparing BMI with electrical measuring of people's body fat found that, if anything, BMI measures underestimate how many people are overweight or obese.
If your doctor thinks your BMI may be misleading, he or she can take your waist measurement to work out if you're overweight. Your doctor will also use his or her judgement to decide if your weight is a health risk for you.