The Nelson Medical Practice

Kingston Road, London, SW20 8DA

111 Out of hours
GP services only, call: 0203 668 3400
All other Health Centre Services, call: 0203 668 3300

Weight management

This service is provided by LiveWell 

Useful information & advice

Am I a healthy weight?

The Body Mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. It is defined as the individual’s body mass divided by the square of their height – with the value universally being given in units of kg/m2.

You are a healthy weight if your BMI is:

  • Caucasian: 18.5 – 25
  • Indian, Asian, Oriental: 18.5 – 23

Calculate your BMI using this NHS Choices tool.

Weight in children

BMI is used differently for children. It is calculated the same way as for adults, but then compared to typical values for other children of the same age. Instead of set thresholds for underweight and overweight, then, the BMI percentile allows comparison with children of the same sex and age. A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese for people 20 and under. People under 20 with a BMI between the 85th and 95th percentile are considered to be overweight.


Obesity is when you have excess body fat that has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems. People are considered obese when their body mass index (BMI) exceeds 30 kg/m2.

Obesity increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, obstructive sleep apnoea, certain types of cancer, and osteoarthritis. It is usually caused by a combination of excessive food energy intake and lack of physical activity.

For more information and advice on obesity see this website:


You are considered underweight if your BMI <18. There are many different causes of being underweight. But it is usually due to lack of food, however illness can also cause it.

Being underweight is just as dangerous for your health as being overweight. Please contact your doctor if you are underweight, especially if you have lost weight suddenly.

Anorexia is an eating disorder of excessive weight loss and usually undue concern about body shape. If you think you or a family member have anorexia, please consult your doctor or see the websites below.