Obesity in adults

Expert reviewer, Mr Paul McArdle, Registered Dietitian
New review due March 2024

Obesity is when you have too much body fat. Nearly two-thirds of adults in the UK are overweight or live with obesity. There are lots of good reasons to stay a healthy weight, or lose excess weight if you need to, and there’s plenty of support out there to help you.

If you have a child and are worried about their weight, see our information on obesity in children.

A woman is eating and reading 

Causes of obesity

Obesity is caused by taking in more energy (calories) in food and drink than your body uses up. But it’s usually more complicated than this and many different things may work together to determine your weight.

What you eat is certainly important. High-calorie foods with a lot of sugar and fat may cost less and be easier to find than more healthy foods, but they may not fill you up so well. Portion sizes and plate sizes are larger now than in the past too, which makes it easy to take in more calories than you need.

It’s part of life to be less active these days because, as a society, we do less manual labour and have lots of labour-saving devices. And it’s easy to sit and watch TV or use computers for hours. Many of us use cars and spend less time walking. But if you’re not physically active, you may be more likely to have problems with obesity.

Obesity also runs in families. If other people in your family have lived with obesity, you’re more likely to as well. If you were overweight or had obesity as a child, you’re also more likely to live with obesity 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.

Sometimes, health conditions and medicines can make you put on weight.

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Measuring obesity

There are several different ways to tell if you have excess body fat.

Body mass index (BMI)

Body mass index (BMI) looks at your weight in relation to your height. If you know these measurements, you can find out your BMI using our BMI calculator.

For most adults, a healthy BMI is between 18.5 and 24.9. The general ranges for BMI are:

  • 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 if you’re from certain ethnic groups, including Asian and African-Caribbean. This is because people from these groups have more risk of health problems from being overweight, even at lower BMI levels.

Waist circumference

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

Your health may be at risk if your waist measurement is:

  • 94 centimetres (37 inches) or more (for men)
  • 80 centimetres (31.5 inches) or more (for women)

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 can use the tests above to check yourself but if you’re unsure, 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 any other health problems.

Benefits of losing weight

If you lose weight, it can help to keep you healthy and may improve your quality of life.

Obesity is associated with a wide range of other health conditions. These include:

If you make some changes and lose weight, you can help to prevent these health conditions. And it will bring long-term health benefits. You may have a healthier heart and bones so you can keep active, for example. And you might also find it boosts your mental health.

How to lose weight

It’s important to get help and support to lose weight when you’re ready to make a start. There’s no quick fix to lose weight but it really is worth it. Even if you only lose a small amount of excess weight, it can improve your health and wellbeing.

The best way to achieve a healthy weight is to improve your diet and eating habits. And to combine this with doing more physical activity.

It's best to start gradually – aim to lose up to 1kg (2lbs) per week. This will allow time for new, healthier habits to become part of your everyday life. It’s helpful to set clear and achievable goals too.

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. So, you might need to reduce how much you eat, as well as what you eat. But make sure you try some healthy changes that you can stick to, and still let you enjoy food.

Speak to your GP or practice nurse for advice before you cut down or change your diet if you have any other health problems.

Fad diets and crash dieting

A fad diet involves eating a very limited range of foods. You can find lots of examples of these on social media. But with these types of diets, although you may lose a lot of weight in the short term, you’ll probably put it back on as soon as you start eating normally again. Crash dieting isn’t a good idea either. If you dramatically cut down how much you eat, your body might not get all the nutrients it needs to be healthy.

Doctors don’t generally recommend very low-calorie diets (fewer than 800kcal per day). But sometimes this may be right for you. You should only follow very low-calorie diets under medical supervision.

Weight-loss programmes

There are several weight-loss groups, clubs and programmes that can support and help you manage your weight. Research shows that these can be helpful for some people. So, this might be something you’d like to try if you like group meetings. But there’s also a range of online diet programmes that can help you lose weight and then keep it off. These can still provide social support through 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 more 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 doing more exercise. Choose activities that fit into your usual routine, such as brisk walking or gardening. It's important to find an activity you enjoy. 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 is good for your health.

If you haven’t done any exercise for some time, start slowly and gradually build up how much you do. If you have other health conditions that might affect how much exercise you can do, get advice from your GP or practice nurse.

Medicines for obesity

If you make changes to your diet and do more exercise, you should start to lose weight. But if you need more help and support, talk to your GP. They may refer you to an NHS weight-management service or suggest a good weight-loss organisation.

Sometimes your GP or specialist doctor may suggest medicines. This is usually only if you’ve changed your diet and are exercising but this hasn’t worked out for you.


Orlistat is a medicine that prevents your body from absorbing fat in your food. Your GP may prescribe it for you if:

  • your BMI is 30 or more and lifestyle changes haven’t worked for you
  • your BMI is 28 or more and you have health problems associated with obesity as well

Orlistat can cause side-effects such as tummy pain and problems with digestion, like diarrhoea. It’s important to follow a low-fat diet to help prevent these problems. Check in with your GP regularly so they can check if the medicine is working and if you have any side-effects. 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.

If you’re pregnant, you might not be able to take orlistat – ask your GP for advice. And if you’re breastfeeding, you shouldn’t take it.

You can also buy orlistat from a pharmacy but at a lower dose, and you’ll need to talk to your pharmacist before you can buy it. They’ll make sure it’s suitable for you.

Liraglutide (Saxenda)

Liraglutide (also known as Saxenda) is a treatment for people who have obesity and high blood glucose, and is used alongside diet and exercise. It works by mimicking natural hormones that are in your body that help to regulate how much you eat.

Your specialist doctor may prescribe it for you if:

  • your BMI is at least 35, or 32.5 if your ethnicity puts you at greater risk of health problems from obesity
  • you have high blood sugar that puts you at risk of developing diabetes
  • you have a high risk of cardiovascular problems, such as heart attacks and strokes

You have liraglutide as an injection once a day and your doctor will gradually increase the dose over a number of weeks. They’ll explain what dose you need and how often. As with orlistat, you may get some side-effects. These may include feeling or being sick, diarrhoea and constipation – for a full list of side-effects, see the patient information leaflet that comes with your medicine.

Surgery for obesity

Sometimes, surgery is an option to treat obesity. The medical term for this is bariatric surgery. The most common types of bariatric surgery are sleeve gastrectomy, gastric bypass and gastric banding. They either reduce the size of your stomach so you eat less, or bypass part of your gut so your body absorbs less food. Your doctor might offer you 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, you may need surgery straightaway.

Your surgeon will talk you through what your operation will involve and the benefits, risks and limitations. Before you have your operation, a specialist team will usually support you to lose weight. This is to make sure that surgery is the right option for you and that it will work.

After the operation, a specialist obesity team will help you to make changes to your diet.

Frequently asked questions

  • The best way to keep the weight off is to make healthy changes to your habits that you can stick to in the long term. This means eating a healthy balanced diet that you enjoy, and being physically active in a way that you enjoy and fits in with your lifestyle.

    Here are some tips on how to keep the weight off.

    • Set some goals and reward yourself when you reach them – maybe treat yourself to a spa day? Whatever motivates you.
    • Accept that there are times you’re going to slip up. Don’t be too hard on yourself – just set yourself back on track.
    • Stay physically active. Try new activities out to see which you enjoy and ask a friend or family to join in, or join a club so you can exercise and meet other people.
    • Check your progress to make sure the weight isn’t creeping back – weigh yourself every week, or keep an eye on 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 having problems making improvements to your diet or reducing how much you eat, make an appointment with your practice nurse. They can give you plenty of advice on diet and exercise, and encourage you to keep going with your weight loss.

    Your practice nurse or GP may 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. A weight-management group may give you just the right type of advice, support and motivation that you need.

    You might find a counsellor or psychologist can help by giving you 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 or an NHS weight-management service.

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Related information

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  • Reviewed by Rachael Mayfield-Blake, Freelance Health Editor, March 2021
    Expert reviewer, Dr Paul McArdle, Registered Dietitian
    New review due March 2024