Obesity in adults

Expert reviewer, Mr Paul McArdle, Registered Dietitian
New review due September 2021

Obesity means having too much body fat. It’s a really common problem these days – nearly two-thirds of adults in the UK are overweight or obese.

Being obese increases your risk of a number of health conditions, including type 2 diabetes, coronary heart disease and some types of cancer. So there are lots of good health reasons for staying a healthy weight, or losing excess weight if you have it.

If you’re concerned your child may be overweight or obese, see our information on obesity in children.

A woman is eating and reading 

Am I obese?

There are several different ways to tell if a person has excess body fat.

Body mass index (BMI)

A common way of deciding if a person is obese is to calculate their body mass index (BMI). This looks at weight in relation to height. If you know your weight and your height, you can find out your BMI using our BMI calculator.

For most adults, a healthy BMI is between 18.5 and 24.9. If you have a BMI greater than this, you’re likely to be overweight or obese. Here are the general ranges for BMI:

  • 25 to 29.9 – overweight
  • 30 to 39.9 – obese
  • over 40 – severely obese

These BMI ranges don’t fit everyone. For example, if you have a lot of muscle, your BMI is likely to be high and may not be a good test of whether you need to lose weight. And these categories aren’t a reliable guide to health risks if you’re from certain ethnic groups, including Asian and African-Caribbean. This is because people from these groups have an increased risk of health problems even at lower BMI levels.

Waist circumference

Your waist circumference is another important measure of whether you have excess fat which may affect your health. If you’re not sure of your waist size, measure around your body halfway between the bottom of your ribs and the top of your hips.

Your health may be at risk if:

  • you're a man and your waist measurement is 94 centimetres (37 inches) or more
  • you’re a woman and your waist measurement is 80 centimetres (31.5 inches) or more

Excess weight is more likely to cause other health problems if you carry the excess around your middle rather than elsewhere.

In your GP surgery

You’ll be able to use the tests above to check for yourself whether you’re carrying excess weight. But you may also wish to contact your GP surgery for advice about your weight.

At your surgery you may see a practice nurse rather than your GP. They’ll check your BMI and waist measurement. They may also measure your blood pressure, arrange blood tests to check your cholesterol, and ask about other health problems.

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How to lose weight

Successful weight loss takes time and effort so think about why you want to lose weight and seek help and support when you’re ready to make changes. There’s no quick fix for losing weight but it really is worth it. Losing even a small amount of excess weight can improve your health and wellbeing. Have a look at our information on losing weight safely.

When you’re ready to change, the best way to achieve a healthy weight is to improve your diet and eating habits. This is likely to be more successful if, at the same time, you increase the amount of physical activity you do.

It's important that you're realistic about the amount of weight you want to lose – don’t try to lose more than 1kg (2lbs) per week. This allows time for new, healthier habits to become part of your everyday life. Make sure that you set yourself clear and achievable goals.

A healthy, balanced diet

To lose weight safely, you need to take in fewer calories than you use up, while still following a healthy balanced diet. This means that you may need to reduce how much you eat, as well as changing what you eat.

For lots of information and useful tips see our topics on losing weight safely and what makes up a healthy balanced diet. The aim is to make healthy changes which you can stick to, and which still let you enjoy your food.

Speak to your GP or practice nurse for advice before cutting down or changing your diet if you have any other medical problems.

Fad diets and crash dieting

A fad diet involves eating a very limited range of foods. Although it may lead to short-term weight loss, you’ll probably put the weight back on as soon as you return to your usual eating habits. Don’t dramatically cut down how much you eat – this may mean your body doesn’t get all the nutrients it needs to be healthy.

Doctors don’t generally recommend very low calorie diets (fewer than 800kcal per day). However, in certain circumstances this may be right for you, so your GP may suggest a diet like this. You should only follow very low calorie diets under medical supervision.

Weight-loss programmes

There are several groups and clubs and commercial weight-loss programmes that can help you manage your weight. You may find slimming clubs useful if you like group meetings and think you would benefit from that type of support. Attending regular weekly sessions at a slimming club has been shown to help people start to lose weight.

There’s a range of online diet programmes which can help you lose weight and then keep it off. You may find these helpful if you’re too busy to attend a group. But it’s a good idea to also get social support, through, for instance, web chats and online discussion forums.

Talk to your practice nurse or GP about which options might work best for you. They can also give you further advice and information about healthy eating or may refer you to a dietitian or an NHS weight-management service.

Physical activity

The best way to lose weight is to combine healthy eating with being more physically active. Choose exercise that fits into your usual routine, for example brisk walking or gardening. It's important to find an activity which you enjoy, to help you stay motivated. Aim to do some physical activity each day – and remember, the more active you are the better. And even if you don’t lose much weight, being more active means you’re less likely to get diabetes and heart disease.

If you haven’t been active for some time, it’s important to start slowly and gradually build up how much you do. If you have other medical conditions which might affect how much exercise you can safely do, get advice from your GP or practice nurse.

For lots more information, see our topics on the benefits of exercise, types of exercise and how to get started.

Medical treatment of obesity

Making changes to your diet and becoming more physically active should help you lose weight. Your GP practice may be able to tell you where you can get further help and support. They may be able to refer you to an NHS weight management service or suggest a reputable weight-loss organisation.

However, in some circumstances, your GP or specialist doctor may suggest medicines or weight-loss surgery. This is usually only if you’re not losing enough weight through changes in diet and exercise alone.


Your GP may suggest you take a medicine called orlistat. Orlistat prevents your body from absorbing all the fat in your food. It’s used for people with a BMI of 30 or more, when lifestyle and behaviour changes haven’t worked. Your GP may also prescribe orlistat if your BMI is 28 or more and you have health problems associated with obesity as well.

Orlistat can cause side-effects such as abdominal (tummy) pain and oily faeces (poo). It’s important that you follow a low-fat diet to help prevent these problems. And you should see your GP regularly to monitor if the medicine is working and if you have any side-effects. It’s important to note that these aren’t the only side-effects of Orlistat. For a full list of side-effects, see the patient information leaflet that comes with your medicine.

Your doctor may advise you not to take orlistat if you’re pregnant. Women who are breastfeeding shouldn’t take it. If you take the contraceptive pill and you find that orlistat gives you diarrhoea, use additional contraception such as condoms.

Orlistat is also available over the counter, but at a lower dose. You’ll need to talk to your pharmacist before you’ll be able to buy it.


Occasionally, surgery is recommended for obesity. The medical term for this is bariatric surgery. The most common types of bariatric surgery are gastric banding, sleeve gastrectomy and gastric bypass. They involve either reducing the size of your stomach so you eat less, or bypassing part of your gut so your body absorbs less food. You may be offered surgery if you:

  • have a BMI of 40 or higher
  • have a BMI between 35 and 40 with a disease that could be improved with weight loss (for example, diabetes or high blood pressure)

To be able to have surgery you should:

  • have tried other suitable ways of losing weight without success
  • are fit for surgery and general anaesthesia
  • agree to a long-term treatment follow-up programme

If you have a BMI of 50 or more, surgery may be the first option.

If you’re considering surgery, your surgeon will talk to you in more detail about its benefits, risks and limitations. You should be offered support to lose weight from a specialist team prior to surgery. This is to make sure that surgery is the right option and that the surgery is successful.

After the operation, you’ll work with a specialist obesity team who’ll help you to make changes to your diet.

Causes of obesity

In simple terms, obesity is caused by taking in more energy (calories) in food and drink than your body uses up. However, there are many different factors that may work together to determine if you become obese.

What you eat is certainly important. For most people, it’s now easy to get hold of high-calorie foods with a lot of sugar and fat. In fact, they may cost less and be easier to find than more healthy foods, but may not fill you up so well. Portion sizes and plate sizes have become larger over the years too, making it easy to take in more calories than you need.

At the same time, people are generally becoming less active. Fewer people do manual labour and we have many labour-saving devices. We sit and watch TV or use computers for hours. Many of us use cars and spend less time walking. If you’re not physically active, you’re more likely to become obese.

Obesity also runs in families. If you were overweight or obese as a child, or other people in your family are, you're more likely to be obese as an adult. Genetic factors play a role in this. But it’s probably also because families tend to share the same environment and habits.

In some cases, medical conditions and medicines can make you put on weight.

Complications and effects of obesity

Being obese can make you feel very uncomfortable and bring lots of day-to-day problems. You may get breathless and find it difficult to walk or be physically active. You may find it hard to find comfortable clothing, and you may find that you sweat a lot.

If you’re obese, this can also affect the way you feel. Your self-esteem and confidence may be low. And because some people view obesity very negatively, you may feel rejected, ashamed and even depressed.

Obesity can lead to a wide range of health problems. These include:

Women who are obese are more likely to have problems during and after pregnancy.

Frequently asked questions

  • You’ve done really well to lose weight. And it’s discouraging to lose weight then put it back on – if this happens to you, you’re certainly not alone. The best way to maintain weight loss is to make healthy changes to your habits that you can stick with in the long term. This means eating a healthy balanced diet that you enjoy, and being physically active in a way that fits in with your lifestyle.

    If you’ve lost weight, there are lots of things you can do to help keep it off. Here are some tips.

    • Accept that there are times you’re going to slip up. Don’t be too hard on yourself – just set yourself back on track.
    • Carry on with your healthy eating, but allow yourself occasional treats. Build in non-food rewards when you reach goals.
    • Stay physically active. Keep looking for new enjoyable activities, perhaps asking a friend or family member to join in.
    • Check your progress to make sure the weight isn’t creeping back – use weighing scales (once a week), or notice how your clothes fit.
    • Plan ahead how much you’re going to eat at special times like holidays, or family celebrations. And stick to it.
    • Get support and encouragement from friends or family members so they can help you keep on track.

    If you’re struggling to keep your weight off, contact your practice nurse. They’ll be able to give you advice and support.

  • If you're having problems improving your diet or reducing how much you eat, make an appointment with your practice nurse. They can advise you on diet and exercise, and encourage you to keep going with your weight loss.

    Your practice nurse or GP may also be able to refer you to a weight-management group. This may be run by the NHS, or they may suggest a commercial group that you pay for. It may be that a weight-management group or slimming group gives just the right type of advice, support and motivation that you need.

    For some people, a counsellor or psychologist can help by giving individual advice and exploring your emotional relationship with food. Ask your GP if referral to a counsellor might be an option for you.

    Also, if available, your GP might be able to refer you to a dietitian.

    You can also find useful information, help and support online from organisations interested in a healthy diet and safe weight loss. See our section ‘Other helpful websites’ below.

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Related information

Tools and calculators

    • Obesity. Oxford Handbook of Nutrition and Dietetics (online). Oxford Medicine Online., published January 2012, updated online December 2015
    • Obesity in adults. BMJ Best practice., last reviewed July 2018
    • Obesity in adults. PatientPlus., last checked January 2015
    • Bariatric surgery. PatientPlus., last checked January 2014
    • Obesity. The MSD Manuals., last full review/revision December 2016
    • Obesity. NICE Clinical Knowledge Summaries., last revised December 2017
    • BMI: preventing ill health and premature death in black, Asian and other minority ethnic groups. National Institute for Health and Care Excellence (NICE), July 2013.
    • Orlistat. NICE British National Formulary., accessed September 2018
    • Health matters: obesity and the food environment. Public Health England., published March 2017
    • Waist measurement. Heart Foundation., accessed September 2018
    • Fad diets. Food fact sheet. BDA: The Association of UK Dietitians, 2014.
    • Weight loss. BDA: The Association of UK Dietitians., published February 2016
    • Jolly, K, Lewis A, Beach J, et al. Comparison of range of commercial or primary care led weight reduction programmes with minimal intervention control for weight loss in obesity: Lighten Up randomised controlled trial. BMJ 2011; 343:d6500. doi:10.1136/bmj.d6500
    • Gudzune K, Doshi R, Mehta A, et al. Efficacy of commercial weight loss programs: an updated systematic review. Ann Intern Med 2015; 162(7):501–12. doi:10.7326/M14-2238
    • Obesity and pregnancy. The American College of Obstetricians and Gynecologists., published April 2016
    • Keeping on track. National Obesity Forum., accessed September 2016
    • Weight management: lifestyle services for overweight or obese adults. Public health Guideline. National Institute for Health and Care Excellence (NICE), May 2014.
  • Reviewed by Dr Kristina Routh, Freelance Health Editor, Bupa Health Content Team, September 2018
    Expert reviewer, Mr Paul McArdle, Registered Dietitian
    New review due September 2021