Body Mass Index (BMI)


The number of people who are overweight or obese is increasing rapidly in many parts of the world. In the UK in 2012, 42% of men and 32% of women were overweight and 24% of men and 25% of women were obese.

What is BMI?

Body Mass Index (BMI) uses your weight and height to determine if you are within the normal, healthy range for weight or if you are underweight, overweight or obese.

The standard BMI ranges for weight categories in adults are:

BMI Weight category
Below 18.5 Underweight
18.5-24.9 Normal weight
25.0-29.9 Overweight
30.0 and above Obese

Why is it important?

Having a low BMI and being underweight may be a sign that you are not eating enough or you have an underlying illness such as an overactive thyroid gland.

People with a BMI above the normal (healthy) range are more likely to suffer obesity-related health problems such as diseases of the heart and blood vessels (cardiovascular disease (CVD)), type 2 diabetes and certain cancers. And CVD, type 2 diabetes, and certain types of cancer and their treatment, can all increase your risk of sexual problems.

How accurate is it?
BMI can tell you if you weigh too much, but it cannot tell you if this is due to too much fat. It does not distinguish between excess fat, muscle or bone mass, and it cannot provide information on how fat is distributed within the body. It also does not account for other factors such as age, sex, ethnicity and muscle mass.

For this reason BMI may be less reliable in certain groups of people, such as:

  • Older individuals who lose muscle with aging – they may fall in the normal (healthy) weight range even though they are carrying too much fat
  • Muscular individuals, or highly trained athletes, who have increased muscle mass – they may be classed as overweight or obese even though they have little body fat
  • Pregnant women – they may be classed as overweight or obese because BMI won’t consider the weight of the pregnancy separately

So, BMI is best used as a ‘screening tool’ to identify people who are overweight or obese. Others factors such as how much fat they have, how this is distributed within the body, their genetics and fitness will all provide more information on their risk of disease.

How can you get it measured?
You can have your BMI measured at your doctor’s surgery or you can check it yourself online using the NHS Choices BMI healthy weight calculator. This is available at:

Why you should measure your waist?

Measuring your waist circumference is a good way to check if you have central (abdominal) obesity and are carrying excess ‘visceral’ fat. This is a dangerous type of fat that surrounds the internal organs. Having too much of it puts you at increased risk of CVD, type 2 diabetes and cancer. Even If your BMI is in the normal (healthy) range, you can still have excess abdominal fat that increases your risk of these diseases.

How do you do it?

  • Feel where the top of your hips are and the bottom of your ribs are
  • Wrap a tape measure around your waist, in the middle of these two points
  • Breathe out as usual, then take the measurement in centimeters (cm)

What does it tell you?
The following table tells you how large your waist has to be for you to have abdominal obesity.

Country or ethnic group Waist circumference What it means What you should do
Europid Caucasian/white skin), Eastern Mediterranean, Middle-East (Arab), Sub-Saharan 94cm or more and you are a man
80cm or more and you are a woman
You have abdominal  obesity Try to lose weight
South Asian, Chinese, Japanese, Ethic South and Central American 90cm or more and you are a man
80cm or more and you are a woman
You have abdominal obesity Try to lose weight
Any 102cm or more and you are a man
88cm or more and you are a woman
You have significant abdominal obesity and are at very high risk See your GP

How accurate is it?
Waist circumference will be less accurate in certain situations, such as pregnancy and swelling of the tummy due to medical conditions.

What should you do if you are overweight or obese?

Losing weight will reduce your risk of obesity-related diseases. The best way to lose weight is through diet and exercise. Medication may be required in some cases. It is sensible to see your doctor so they can check your general health and advise you on the best way forward.

Where can you get more information?

The Sexual Advice Association is here to help. We cannot give individual medical advice, but we can answer your questions on any sexual problems and put you in touch with local specialist practitioners. We also have a number of factsheets and booklets on sexual problems and related issues for men and women that can be downloaded from our website or requested. Please feel free to email us or phone our Helpline (our contact details are at the bottom of this page).

You can also visit the NHS Choices website at for information and advice on many different health and lifestyle topics.

What is the Take Home Message?

Being overweight or obese can put you at risk of serious health problems – it’s never too late to lose weight!

Further reading

Download or request our booklet ‘Sex and diabetes’ and/or our factsheet ‘The Mediterranean Diet


By donating to the Sexual Advice Association, you will know that you are helping improve the lives of people living with sexual problems. If you are interested in donating, please click here or contact us for more information (details at the bottom of this page).

Thinking About Sex Day: February 14th

Launched by the Sexual Advice Association, Thinking About Sex Day (TASD) is designed to encourage everyone to think about the physical and psychological issues surrounding sexual activity.

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