Obesity in adults

Your health expert: Dr Imran Khan, Lead Physician at Bupa
Content editor review by Victoria Goldman, August 2023
New review due August 2026

Obesity is when you have too much body fat that may affect your health. 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.

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

Causes of obesity

Obesity is caused by taking in more energy (calories) in food and drink than your body uses up. But lots of other things can affect your weight as well. Obesity is often caused by a combination of different things.

What you eat

High-calorie foods containing a lot of sugar and fat may cost less and be easier to find than more healthy foods.  Portion sizes and plate sizes are larger now than in the past.

How active you are

Many people are less active these days. Fewer jobs involve physical work, and many people use a car or public transport rather than walk. If you’re not physically active, you may be more likely to have problems with obesity.

Your family background

Obesity 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. Obesity may be linked to specific genes. But it’s probably also because families tend to share the same environment, culture and lifestyle habits.

Your general health

Lots of things can make you more likely to be overweight or obese, such as sleep problems and hormonal problems. Researchers have found that the balance of bacteria, fungi and other organisms living naturally in your gut can affect your appetite and how your body stores fat. Sometimes, having certain health conditions and taking certain medicines can make you put on weight. You may be more likely to eat high-fat, high-calorie foods if you’re feeling down or anxious.

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 suit everyone. For example, if you have a lot of muscle or are over 65. They also aren’t reliable if you’re from certain ethnic groups, including Asian and African-Caribbean. This is because people in these ethnic groups are more likely to have certain health problems, even at lower BMI levels.

Waist circumference

Your waist circumference measures if you have excess fat around your middle. To check your waist circumference, 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)

Carrying more weight around your middle may cause other health problems, such as high blood pressure and type 2 diabetes.

In your GP surgery

You can use the above tests to check your weight. But if you’re unsure, contact your GP surgery for advice.

Your GP surgery will be able to direct you to the best person to speak to about your weight. They’ll check your BMI and waist measurement. They may also:

  • measure your blood pressure
  • arrange blood tests to check your cholesterol
  • ask about any other health problems

Benefits of losing weight

Losing weight 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:

Losing weight can have other long-term health benefits. If your bones and heart are healthier, you may find it easier to keep active. Losing weight may boost your mental health too.

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, this can improve your health and wellbeing.

The best way to achieve a healthy weight is to improve your diet and eating habits. Doing more physical activity will help you too. 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.

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.

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. You may need to reduce how much you eat, as well as change what you eat. Choose healthy changes that you can stick to and will 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 may lose a lot of weight in the short term, but 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 may 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

Several weight-loss groups, clubs and programmes may support and help you manage your weight. Using online diet programmes and apps may help you lose weight and keep it off. Many of these provide social support through web chats and online discussion forums.

Talk to your practice nurse or GP about which options may work best for you. They can also:

  • give you more advice and information about healthy eating
  • refer you to a dietitian
  • refer you to NHS weight-management services

Physical activity

Aim to do some physical activity each day – and remember, the more active you are, the better. Even if you don’t lose much weight, being more active is good for your health. Choose activities that fit into your usual routine, such as brisk walking or gardening. It's important to find an activity you enjoy.

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 may affect how much exercise you can do, get advice from your GP or practice nurse.

Emotional support

Losing weight can be a challenge for many people. Even if you know how to lose weight, it’s not always easy to change your habits and keep the weight off. You need to find a healthy eating and activity plan that works for you. It’s also important to celebrate every weight-loss success, however small. You may find it easier if you try to lose weight with a friend or family member, or join a local support group.

Being overweight may affect your self-esteem and mental health. If you’re feeling stressed, you may be more likely to overeat and put on weight. Learning how to deal with stress may help you lose weight – if you feel like comfort eating, go for a walk or try meditation or deep breathing.

Speaking to a counsellor or psychologist may also help you lose weight and keep it off. You can discuss with them how you feel about being overweight, and the best ways for you to make some lifestyle changes. Your GP may be able to refer you to a counsellor.

Bupa Weight Management Plan

The Bupa weight management plan is designed for people with a BMI over 30 (or over 27 if you have a weight related condition). The plan is designed to empower you to achieve and maintain a healthy weight in a sustainable way.

To book or to make an enquiry, call us on 03452660566

Medicines for obesity

Sometimes your GP or specialist doctor may suggest that you take some medicines to help you lose weight. You’ll usually be offered obesity treatment if changing your diet and exercising hasn’t worked out for you.

Your doctor may prescribe several different medicines. It’s important to check with your doctor or pharmacist regularly to make sure the medicines are working and to discuss any side-effects. For a full list of side-effects, see the patient information leaflet that comes with your medicine.

If you stop taking the medicines, you’re likely to put on weight again.


Orlistat stops your body from absorbing fat in your food. Your GP may prescribe it 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

You take orlistat as a tablet. It can cause side-effects, such as tummy pain and diarrhoea. Eat a low-fat diet to help to prevent these side-effects.

You may be able to buy orlistat from a pharmacy but at a lower dose. Speak to your pharmacist first to check it’s suitable for you.

Liraglutide (Saxenda)

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

Your specialist doctor may prescribe it 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 makes you more likely to have diabetes
  • you have a high risk of cardiovascular problems, such as heart attacks and strokes

You have liraglutide as an injection – your doctor will tell you how much, and how often. You also need to eat a healthy diet and keep active. Side-effects may include feeling or being sick, diarrhoea and constipation.

Semaglutide (Wegovy)

Semaglutide (also known as Wegovy) is a treatment for weight loss in people who have at least one weight-related medical condition. It works for weight loss by regulating your appetite and blood sugar levels.

Semaglutide is used as part of a specialist weight management service in people who have either:

  • a body mass index (BMI) of at least 35.0 kg/m2 and a weight-related health condition
  • a BMI of 30.0 kg/m2 to 34.9 kg/m2 and are suitable for a referral to specialist weight management services

Semaglutide may be prescribed to people with a lower BMI in certain ethnic groups, including Asian and African-Caribbean.

You have semaglutide as an injection. You also need to eat a reduced-calorie diet and be physically active.

Surgery for obesity

Surgery to treat obesity is called bariatric surgery. The most common types of bariatric surgery are sleeve gastrectomy, gastric bypass and gastric banding. These either reduce the size of your stomach so you eat less, or bypass part of your gut so your body absorbs less food. Bariatric surgery may also change the balance of bacteria, fungi and other organisms that live naturally in your gut – this may help weight loss and prevent weight gain.

Your doctor may offer you bariatric surgery if you:

  • have a BMI of 40 or higher
  • have a BMI between 35 and 40 with a disease that may improve with weight loss (such as diabetes or high blood pressure)

To be able to have surgery you should:

  • have tried other suitable ways of losing weight without success
  • befit 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.

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

It can be difficult to keep your weight within a healthy range. But it may help if you set appropriate goals. You can usually achieve this by eating a healthy balanced diet and being more physically active. For more information, see our how to lose weight section.

Your GP surgery can direct you to the best person to give you support. This may be a nurse, a dietitian or a local weight-management group. You could join a local weight-loss support group yourself. For more information, see our how to lose weight section.

You may put on weight if you take in more calories in food and drink than you are using up during daily physical activity. But lots of other things can cause obesity, such as your family background, medical history and your physical and mental health. For more information, see our causes of obesity section.

Obesity is linked to several long-term health conditions, including type 2 diabetes, heart problems and joint problems. It can affect people’s mental health too. Losing weight can help to improve your overall health and quality of life. For more information, see our benefits of losing weight section.

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