Obesity

The term obese describes a person who has excess body fat.

In the UK it's estimated that around 1 in every 4 adults and around 1 in every 5 children aged 10 to 11 are living with obesity.

How to tell if you're living with obesity

The most widely used method to check if you're a healthy weight is body mass index (BMI).

Body mass index (BMI)

BMI is a measure of whether you're a healthy weight for your height. You can use the NHS BMI healthy weight calculator to find out your BMI.

For most adults, if your BMI is:

below 18.5 – you're in the underweight range
18.5 to 24.9 – you're in the healthy weight range
25 to 29.9 – you're in the overweight range
30 to 39.9 – you're in the obese range
40 or above – you're in the severely obese range

If you have an Asian, Chinese, Middle Eastern, Black African or African-Caribbean family background you'll need to use a lower BMI score to measure overweight and obesity:

23 to 27.4 – you're in the overweight range
27.5 or above – you're in the obese range

BMI score has some limitations because it measures whether a person is carrying too much weight but not too much fat. For example, people who are very muscular, like professional sportspeople, can have a high BMI without much fat.

But for most people, BMI is a useful indication of whether they're a healthy weight.

Waist to height ratio

Another measure of excess fat is waist to height ratio, which can be used as an additional measure in adults who have a BMI under 35.

To calculate your waist to height ratio:

Find the middle point between your lowest rib and your hip bone. This should be roughly level with your belly button.
Wrap the tape measure around this middle point, breathing naturally and not holding your tummy in.
Take your measurement and divide it by your height, measured in the same units (for example, centimetres or inches).

For example, if your waist is 80cm and you are 160cm tall, you would calculate your result like this: 80 divided by 160, which equals 0.5.

A waist to height ratio of 0.5 or higher means you may have increased health risks.

How to measure your waist

This video explains how to measure your waist so you can calculate your waist to height ratio.

Displays the text version below the video

Plays the video with descriptive audio

Media last reviewed: 10 November 2023
Media review due: 10 November 2026

Risks of living with obesity

Obesity is a serious health concern that increases the risk of many other health conditions.

These include:

type 2 diabetes
coronary heart disease
some types of cancer, such as breast cancer and bowel cancer
stroke

Living with overweight and obesity can also affect your quality of life and contribute to mental health problems, such as depression, and can also affect self-esteem.

Causes of obesity

Obesity is a complex issue with many causes. Obesity and overweight is caused when extra calories, particularly those from foods high in fat and sugar, are stored in the body as fat.

Obesity is an increasingly common problem because the environment we live in makes it difficult for many people to eat healthily and do enough physical activity.

Genetics can also be a cause of obesity for some people. Your genes can affect how your body uses food and stores fat.

There are also some underlying health conditions that can occasionally contribute to weight gain, such as an underactive thyroid gland (hypothyroidism), although these types of conditions do not usually cause weight problems if they're effectively controlled with medicines.

Some medicines can also make people more likely to put on weight, including steroids and some medicines for high blood pressure, diabetes or mental health conditions.

Treating obesity

The best way to treat obesity is to eat a healthy reduced-calorie diet and exercise regularly.

To do this, you can:

eat a balanced calorie-controlled diet as recommended by a GP or weight loss management health professional (such as a dietitian)
take up activities such as fast walking, jogging, swimming or tennis for 150 to 300 minutes (2.5 to 5 hours) a week

You may benefit from joining a local weight management programme with group meetings or online support. Your GP can tell you about these.

You may also benefit from receiving support and counselling from a trained healthcare professional to help you better understand your relationship with food and develop different eating habits.

If you're living with obesity and lifestyle and behavioural changes alone do not help you lose weight, a medicine called orlistat may be recommended.

If taken correctly, this medicine works by reducing the amount of fat you absorb during digestion. Your GP will know whether orlistat is suitable for you.

A specialist may prescribe other medicines called liraglutide or semaglutide. They work by making you feel fuller and less hungry.

For some people living with obesity, a specialist may recommend weight loss surgery.

Outlook

Managing a complex issue like obesity can be hard. Losing weight takes time and commitment.

The healthcare professionals involved with your care can provide encouragement and advice about how to mange your weight, build healthy lifestyle habits and maintain weight loss achieved.

Completing a weight management programme, regularly monitoring your weight, setting realistic goals, and involving your friends and family with ways to lose weight can also help.

It's important to remember that losing what seems like a small amount of weight, such as 3% or more of your original body weight, and maintaining this for life, can significantly reduce your risk of developing obesity-related complications like diabetes and heart disease.

Information:

Social care and support guide

If you:

need help with day-to-day living because of illness or disability
care for someone regularly because they're ill, disabled or because of their age (including family members)

Our guide to care and support explains your options and where you can get support.

Couch to 5K

If it's been a long time since you did any exercise, you should check out the Couch to 5K running plan.

It consists of podcasts delivered over the course of 9 weeks and has been specifically designed for absolute beginners.

To begin with, you start running for short periods of time, and as the plan progresses, gradually increase the amount.

At the end of the 9 weeks, you should be able to run for 30 minutes non-stop, which for most people is around 5 kilometres (3.1 miles).

Obesity is a complex issue with many causes. It's caused when extra calories are stored in the body as fat.

If you consume high amounts of energy, particularly found in high fat and high sugar foods, and do not use all of the energy through physical activity, much of the extra energy will be stored in the body as fat.

Calories

The energy value of food is measured in units called calories. The average physically active man needs about 2,500 calories a day to maintain a healthy weight, and the average physically active woman needs about 2,000 calories a day.

This amount of calories may sound high, but it can be easy to reach if you eat certain types of food. For example, eating a large takeaway hamburger, fries and a milkshake can total 1,500 calories – and that's just 1 meal. For more information, read our guide to understanding calories.

As well as this, many people do not meet the recommended physical activity levels for adults, so excess calories consumed end up being stored as fat in the body.

Diet

Diet and lifestyle factors contribute to development of obesity and overweight. Some of the most common ones are:

eating large amounts of processed or fast food – this is food that's high in fat and sugar
drinking too much alcohol – alcohol contains a lot of calories
eating out a lot – food cooked in a restaurant may be higher in fat and sugar
eating larger portions than you need
drinking too many sugary drinks – including soft drinks and fruit juice
comfort eating – some people may comfort eat due to many other factors affecting their life such as low self-esteem or low mood

Changes in society have also made it more difficult to have a healthy diet. High calorie food has become cheaper and more convenient, and is heavily advertised and promoted.

Read about eating less saturated fat and how to cut down on sugar in your diet.

Physical activity

Lack of physical activity is another important factor related to obesity. Many people have jobs that involve sitting at a desk for most of the day. They also rely on their cars, rather than walking or cycling.

For relaxation, many people tend to watch TV, browse the internet or play computer games, and rarely take regular exercise.

If you are not active enough, you do not use the energy provided by the food you eat, and the extra energy you consume is stored by the body as fat.

The Department of Health and Social Care recommends that adults do at least 150 minutes of moderate-intensity aerobic activity, such as cycling or fast walking, every week. This does not need to be done all in a single session, but can be broken down into smaller periods. For example, you could exercise for 30 minutes a day for 5 days a week.

If you're living with obesity and trying to lose weight, you may need to do more exercise than this. It may help to start off slowly and gradually increase the amount of exercise you do each week.

Read more about the physical activity guidelines for adults.

Genetics

There are some genes associated with obesity and overweight. In some people, genes can affect how their bodies change food into energy and store fat. Genes can also affect people's lifestyle choices.

There are also some rare genetic conditions that can cause obesity, such as Prader-Willi syndrome.

Certain genetic traits inherited from your parents – such as having a large appetite – may make losing weight more difficult, but they do not make it impossible.

In many cases, obesity is more to do with environmental factors, such as not having easy access to healthy food, or unhealthy eating habits learned during childhood.

Medical reasons

In some cases, underlying medical conditions may contribute to weight gain. These include:

an underactive thyroid gland (hypothyroidism) – where your thyroid gland does not produce enough hormones
Cushing's syndrome – a rare disorder that causes the over-production of steroid hormones

However, if conditions such as these are properly diagnosed and treated, they should pose less of a barrier to weight loss.

Certain medicines, including some steroids, medications for epilepsy and diabetes, and some medications used to treat mental illness – including some antidepressants and medicines for schizophrenia – can contribute to weight gain.

Weight gain can sometimes be a side effect of stopping smoking.

Published: Jan 10, 2025

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