Body mass index (BMI) is widely used as a simple and reliable way of finding out whether a person is a healthy weight for their height.
For most adults, having a BMI of 18.5 to 24.9 means you're considered to be a healthy weight. A person with a BMI of 25 to 29.9 is considered to be overweight, and someone with a BMI over 30 is considered to be obese.
While BMI is a useful measurement for most people, it's not accurate for everyone.
For example, the normal BMI scores may not be accurate if you're very muscular because muscle can add extra kilos, resulting in a high BMI when you're not an unhealthy weight. In such cases, your waist circumference may be a better guide.
What's considered a healthy BMI is also influenced by your ethnic background. The scores mentioned above generally apply to people with a white background. If you have an ethnic minority background, the threshold for being considered overweight or obese may be lower.
BMI should not be used to work out whether a child is a healthy weight, because their bodies are still developing. Speak to your GP if you want to find out whether your child is overweight.
If you're overweight or obese, visit your GP for advice about losing weight safely and to find out whether you have an increased risk of health problems.
Your GP may ask about:
- your lifestyle – particularly your diet and how much physical activity you do; they'll also ask you whether you smoke and how much alcohol you drink
- any possible underlying causes for your obesity – for example, if you're taking medication or have a medical condition that may contribute to weight gain
- how you feel about being overweight – for example, if it makes you feel depressed
- how motivated you are to lose weight
- your family history – as obesity and other health conditions, such as diabetes, are often more common in families
As well as calculating your BMI, your GP may also carry out tests to determine whether you're at increased risk of developing health complications because of your weight.
These could include measuring your:
- blood pressure
- glucose (sugar) and cholesterol levels in a blood sample
- waist circumference (the distance around your waist)
People with very large waists – generally, 94cm or more in men and 80cm or more in women – are more likely to develop obesity-related health problems.
Your GP may also take your ethnicity into account because it can affect your risk of developing certain conditions. For example, some people of Asian, African or African-Caribbean ethnicity may be at increased risk of high blood pressure (hypertension). Healthy waist measurements can also be different for people from different ethnic backgrounds.
After your assessment, you'll be offered an appointment to discuss the results in more detail, ask any questions that you have, and fully explore the treatment options available to you.