Obesity in adults

Expert reviewer Dr Adrian Raby, General Practitioner and Clinical Lecturer
New review due May 2019

Obesity is a condition in which excess body fat accumulates and may lead to health problems. We’re probably all aware it’s a really common problem these days – around one in four people in the UK are obese.

Obesity usually happens as a result of eating too many calories (energy) and not doing enough physical activity, but other causes may be involved. Being obese increases your risk of a number of health conditions including type 2 diabetes, coronary heart disease and some types of cancer.

There are lots of good health reasons for staying a healthy weight, or losing excess weight if you have it. Losing even a small amount of excess weight can improve your health and wellbeing.

Diagnosis of obesity

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 an accurate measurement of whether you need to lose weight. In addition, these categories aren’t a reliable guide to risk 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.

Your waist circumference is another important measure of your health. 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

Waist apples

Again, these measurements vary depending on your ethnic group – contact your GP surgery for more information. 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.

Checking your weight and making lifestyle changes to lose excess weight are positive steps you can take for yourself (see our section ‘Self-help for obesity’). It’s advisable to contact your GP surgery if you’ve already tried to lose excess weight through lifestyle changes but these haven’t helped. For example, you may have already tried increasing how much activity you do and reducing how much you eat, but not lost weight.

If you contact your surgery, you may see a practice nurse rather than your GP. But whoever you see, they may organise for you to have your blood pressure measured, have blood tests to check your cholesterol, and check for other health problems as well as offer advice about diet and exercise.

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Self-help for obesity

Effective 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. 

If you’ve decided that 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 that you do. It can be daunting making changes, but there are some tips and tricks that can help – see our blog from Behavioural Scientist, Sarah O’Farrell about How to design your environment to help you eat healthier.

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. 

Your GP practice may be able to tell you where you can get further help and support. They may be able to signpost you to a reputable weight-loss organisation or refer you to a dietitian, for example. See our FAQ ‘Getting help with healthy eating’, and ‘Other helpful websites’. 

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 let you still 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. These diets aren't healthy and although they may lead to short-term weight loss, you’re likely to put the weight back on as soon as you return to your usual eating habits. Don’t dramatically cut down how much you eat as it may mean your body doesn’t get all the nutrients it needs to function healthily. Doctors don’t generally recommend very low calorie diets (less than 800 Kcal per day). However, in certain circumstances, this may 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 consistent support. Attending regular weekly sessions at a slimming club has been shown to be effective at helping people start to lose weight. 

There’s a range of online diet programmes available, which can help you lose weight and maintain your weight loss. 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 GP or practice nurse about which options will suit your individual needs and fit in with your lifestyle. They can also give you further advice and information about healthy eating or may refer you to a dietitian. 

Physical activity

The best way to lose weight is to combine healthy eating with increased physical activity. It’s a good idea to choose exercise that you can fit into your usual routine, for example brisk walking or gardening. It's important that you find an activity that you enjoy to help you stay motivated. Aim to do some physical activity at least five days a week. 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. 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 recommended for people with a BMI of 30 or more for whom lifestyle and behaviour changes haven’t been effective. Your GP may prescribe orlistat if your BMI is 28 or more and you also have health problems associated with obesity.

Your GP will discuss the advantages and disadvantages of orlistat with you. The medicine can cause side-effects such as abdominal (tummy) pain and oily faeces. It’s important that you follow a low-fat diet to help prevent these problems. And it’s important to have regular follow-up appointments with your GP to monitor if the medicine is working and if you have any side-effects. 

Your doctor may advise you not to take orlistat if you’re pregnant. Women who are breastfeeding should not take it. For more information, see our FAQ ‘Orlistat and pregnancy’.

Orlistat is also available over the counter, but at a lower dose. You will need to talk to your pharmacist before he or she will sell it to you. 


Occasionally, surgery is recommended for obesity. The medical term for this is bariatric surgery. Two common types of surgery are gastric banding 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 able to have 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)
  • 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 and you will need to see a specialist. The specialist will talk to you in more detail about the benefits and limitations of surgery. After the operation, you’ll work with a specialist obesity team who will 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 energy-dense foods with a lot of sugar and fat. In fact, they may cost less and be easier to find than more healthy foods. The availability of unhealthy foods is also a key factor – the buy-one-get-one-free offers in supermarkets, for example. And portion sizes and plate sizes have become larger over the years. It’s not difficult 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 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.

Occasionally, 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 are 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. 

It’s important for your health to know that 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.

So, there are lots of really good reasons to make the decision to lose your excess weight. And the good news is that losing even a small amount of weight can improve your health. See our section ‘Self-help for obesity’ to get started.

Frequently asked questions

  • Your GP may advise you not to take orlistat if you’re pregnant, and you won’t be able to buy it over the counter. You shouldn’t take orlistat while breastfeeding. This is to protect your baby, as doctors aren’t yet sure whether or not orlistat is safe during pregnancy or if it crosses over into your breast milk.  

    If you’re sexually active, make sure that you use contraception while taking orlistat. If you take the contraceptive pill and you find that orlistat gives you diarrhoea, use additional contraception such as condoms.

    If you’re planning to have a baby or you have become pregnant while taking weight-loss medicine, talk to your GP or pharmacist.

  • 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. There’s no quick fix. Your weight will creep back on if you go back to your old habits. 

    More information

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

    • Carry on with your healthy eating, but allow yourself occasional treats.
    • Stay physically active – don’t go back to bad habits of being very inactive. Keep looking for new enjoyable activities, perhaps asking a friend or family member to join in.
    • Accept that there are times you’re going to slip up and eat too much or give up your activities. Don’t be too hard on yourself and don’t give up altogether – just set yourself back on track.
    • Check yourself regularly to make sure the weight isn’t creeping back – use weighing scales (once a week), or notice how your clothes fit.
    • Don’t let your portion sizes creep up.
    • Make a definite plan beforehand about 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. Talk to them about how important keeping a healthy weight is for you, and how they can help you keep on track.

    Remember that you’re improving your health by losing even a small amount of weight and keeping it off. If you’re struggling to keep your weight off, contact your practice nurse. They’ll be able to give you advice and support to help you keep on track.

  • There is help out there. 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. They can help you find new ways to make links between your emotions, thoughts and your eating patterns. It might not be available in all areas, but it may be worth asking 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 qualified dietitian. A registered dietitian can give you advice on all aspects of your diet. They must be qualified to university degree level and registered with the Health Professionals Council to use the title, 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’.

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Related information

Tools and calculators

    • Obesity. Oxford handbook of nutrition and dietetics (online). Oxford Medicine Online., published December 2015
    • Obesity in adults. BMJ Best practice., last updated 28 January 2016
    • Obesity. Medscape., updated 25 August 2015
    • Obesity in adults. PatientPlus., last checked 9 January 2015
    • Obesity. NICE Clinical Knowledge Summaries., last revised June 2015
    • Obesity: identification, assessment and management. National Institute for Health and Care Excellence (NICE), 2014.
    • 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.
    • Laparascopic gastric plication for the treatment of severe obesity. National Institute for Health and Care Excellence (NICE), November 2012.
    • Orlistat. Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press., accessed 19 April 2016
    • Map of Medicine. Obesity in adults. International View. London: Map of Medicine; 2015 (Issue 5)
    • Shaw K, Gennat H, O'Rourke P, et al. Exercise for overweight or obesity. Cochrane Database of Systematic Reviews 2006, Issue 4. doi:10.1002/14651858.CD003817.pub3
    • Adult obesity. Public Health England., accessed 14 April 2016
    • Understanding adult overweight and obesity. National Institute of Diabetes and Digestive and Kidney Diseases., published December 2012
    • Waist circumference and waist–hip ratio. Report of a WHO expert consultation, 2011.
    • Weight loss. BDA, The Association of UK Dietitians, 2013.
    • Fad diets. BDA, The Association of UK Dietitians, 2014.
    • Weightwise. BDA, The Association of UK Dietitians, 2013.
    • What do dietitians do? BDA, The Association of UK Dietitians., accessed 20 April 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
    • Losing weight. Weightconcern., accessed 14 April 2016
    • Foresight – Tackling obesities: future choices – project report (2nd edition). Government Office for Science, 2007.
    • Xenical 120mg hard capsules. electronic Medicines Compendium., published 23 October 2015
    • Alli 60 mg hard capsules. electronic Medicines Compendium., published 1 April 2016
    • Keeping on track. National Obesity Forum., accessed 20 April 2016
    • What your doctor can offer. National Obesity Forum., accessed 20 April 2016
  • Reviewed by Natalie Heaton, Specialist Health Editor, Bupa Health Content Team, May 2016
    Peer reviewed by Dr Adrian Raby, General Practitioner and Clinical Lecturer
    New review due May 2019

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