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Obesity Is a Disease

9 min read time

Written by: Hannah Thornley

Medically reviewed by: Jennifer Kaur

Published 22/10/2026 Updated 22/10/2026

Key takeaways

Obesity is a chronic, complex disease influenced by factors beyond personal choice.
BMI can help identify risk but doesn’t give a complete picture of health.
Sustainable lifestyle changes to diet, exercise, sleep, and stress can support weight loss.
GLP-1 medicines may help suitable patients by reducing hunger and increasing fullness.
Because obesity is a relapsing disease, long-term weight management may be needed.

Losing weight is often made to sound easy: eat less, move more, and weight loss will follow. But living with obesity isn’t a personal choice. Obesity is a disease that’s influenced by much more than willpower to control how much you eat or exercise.

Obesity is also increasingly common. In 2023 to 2024, an estimated 26.5% of adults in England were living with obesity. There isn’t one reason why so many people are affected. Many biological and environmental factors can make losing weight and keeping it off harder for some people than others.

Here, we look at what causes obesity, how it can affect your health, why losing weight can be difficult, and the lifestyle changes and medical treatments that can help.

Start a weight management consultation to explore the lifestyle and treatment options that may be suitable for you.

Is obesity a disease?

Yes, obesity is now a disease. The World Health Organisation (WHO) recognises obesity as a chronic, complex and relapsing disease, which means it can last for a long time, is influenced by many factors and can return even after successfully losing weight.

More specifically, clinical obesity is defined as a long-term illness where excess body fat affects how the body, tissues or organs function. It can increase your risk of conditions like:

Type 2 diabetes
High blood pressure
Heart disease
Sleep apnoea

Obesity is usually identified using body mass index (BMI), with a BMI of 30 or above classed as obese. But recognising obesity as a disease isn’t about defining someone by their weight, and it doesn’t mean everyone with a BMI of 30+ has the same health risks.

Instead, recognising obesity as a disease helps challenge the stigma that it’s simply the result of poor choices or not trying hard enough. The reasons people develop obesity and find it difficult to lose weight are much more complicated.

Why obesity is not simply a decision

To lose weight, you’ve got to use more energy than you take in. But how hungry you feel and the way your body responds when you lose weight aren’t entirely within your control.

Your weight can be influenced by:

Hormones: Hormones help control your appetite. When you lose weight, changes to these signals can make you hungrier than normal, while your body simultaneously needs less energy at a lower weight. Together, this can make losing more weight harder.

Genetics: There isn’t one “obesity gene.” Several genetic differences affect appetite, fullness, metabolism and how your body stores fat, so some people are genetically more likely to gain weight than others.

Environment: Your circumstances can affect access to healthy food and opportunities to be active. Cheap, ultra-processed foods and larger portions can make it easier to overeat, while poor sleep, stress and some medicines also influence appetite and activity levels.

If you’ve ever wondered “why can’t I lose weight?”, these factors may help explain why. Two people making similar changes can have very different weight loss experiences, because obesity is a disease, not a decision.

Why BMI does not tell the full story

A BMI of 30 or above is used to identify obesity, but the number alone can’t tell you how your weight is affecting your health. BMI can’t:

Directly measure body fat
Show where fat is stored in the body
Account for differences in muscle mass

Doctors may look at your waist-to-height ratio and other aspects of your health to get a better picture of your risk of weight-related health problems.

Ethnicity matters too, because people from some Asian, Middle Eastern, Black African and African-Caribbean backgrounds can develop weight-related health problems at a lower BMI. NICE recommends lower BMI thresholds when assessing obesity in these groups.

How to lose weight and improve health

To lose weight, you need to be in a calorie deficit, which means taking in less energy than your body uses. But you don’t need to rely on a crash diet or an intense exercise plan to achieve one.

Instead, try smaller changes you can realistically stick with:

Base your meals around a balanced diet of nutritious foods, including fruit and vegetables, wholegrains and healthy fats.

Include plenty of protein from foods like eggs, fish, lean meat, beans, lentils and yoghurt, which can help you feel full and maintain muscle while losing weight.

Increase your fibre intake with fruit, vegetables, wholegrains, beans and pulses to help you feel fuller for longer and support digestive health.

Find ways to move more during the day. Government guidelines recommend choosing an activity you enjoy, whether that’s walking, swimming, cycling or something else.

Include resistance exercise such as weights or bodyweight exercises to help preserve muscle as you lose weight.

Prioritise sleep and stress management, as both can affect your appetite and how easy it is to stick to other healthy changes.

Get behavioural support if you need it. This may be useful if emotional eating or your relationship with food is making weight management more difficult.

How GLP-1 weight management treatments can help

For some people living with obesity, lifestyle changes aren’t enough on their own. If they meet the prescribing criteria, GLP-1 weight management treatments can help. GLP-1 medications work alongside healthy eating and exercise and can make these changes easier to maintain.

Several GLP-1 weight loss treatments are available in the UK, including:

Weight loss injections like Wegovy and Mounjaro
Oral weight loss tablets such as the Wegovy pill and Foundayo

All are prescription-only and aren’t suitable for everyone, so you’ll need a clinical assessment before starting. Results vary, and GLP-1 side effects can occur.

These treatments target a natural hormone pathway involved in appetite. They help to reduce your hunger and help you feel full after eating, which can make it easier to eat less and choose healthier foods. Over time, this supports weight loss.

Explore our weight-management medications to learn more about the additional support that may be available to you.

Why obesity care may need to be long-term

While weight loss is one part of obesity treatment, maintaining it is another. The biological and environmental factors that influence hunger and weight don’t disappear once you reach your goal

If you’re using GLP-1 medication, this is particularly relevant. After stopping, hunger can increase, and weight regain is common. Some people choose to stay on treatment to keep appetite under control after reaching a healthy weight, known as maintenance therapy.

Your needs can also change during treatment. You may reach a weight-loss plateau, experience side effects or notice changes in your appetite. Long-term support helps manage these changes so your treatment can be adjusted instead of treating weight loss as a finish line.

Complete a weight-management consultation to explore available treatment options and lifestyle support that may be clinically suitable.

FAQs

Is obesity really a disease?

Yes. Obesity is a disease, not a decision. It is influenced by biological, genetic, behavioural and environmental factors and typically requires long-term management to help maintain weight loss and reduce related health risks.

Is obesity caused by a lack of willpower?

No, obesity is not caused by a lack of willpower. What you eat and how active you are affect your weight, but genetics, appetite hormones, sleep, stress, medications and your environment can all influence hunger, eating habits and weight.

How common is obesity in the UK?

In 2023 to 2024, 26.5% of adults in England were living with obesity, while 64.5% were either overweight or living with obesity. These figures are for England, not the UK, so rates may differ across Scotland, Wales and Northern Ireland.

Can obesity be cured?

Obesity is generally considered a disease that can be managed rather than cured. Even after reaching a healthy weight, some people need ongoing lifestyle support, medication or other treatment to help stop them from putting weight back on.

How can I lose weight safely?

Aim for gradual weight loss through changes to your diet and activity levels that you can realistically maintain. Eating enough protein and fibre, staying active, and getting enough sleep all help. If lifestyle changes haven’t been enough, weight loss medication may be suitable.

Can GLP-1 medicines help with obesity?

Yes, GLP-1 medicines are licensed for obesity in suitable patients in the UK and support weight loss. Treatments such as Wegovy and Mounjaro are prescription-only and aren’t suitable for everyone, so you’ll need a clinical assessment before starting treatment.

Will I regain weight after stopping treatment?

Weight regain is common after stopping treatment with a GLP-1. In clinical trials, people gained around two-thirds of the weight they lost within a year. Many people stay on treatment after reaching their goal weight to help keep weight off.

How we reviewed this article:

Obesity as a Disease: The Obesity Society 2018 Position Statement. (2019) PubMed. [Accessed 22 October 2026]
Obesity profile: May 2025 update. (2025) GOV.UK, Office for Health Improvement and Disparities. [Accessed 22 October 2026]
Obesity and overweight. (2026) World Health Organization. [Accessed 22 October 2026]

Current version
22nd Oct 2026 Written by: Hannah Thornley, BSc Human Physiology
22nd Oct 2026 Medically reviewed by: Jennifer Kaur, MRpharmS

Medically reviewed by:

Jennifer Kaur MRpharmS

I began my journey as a pharmacist, over 15 years ago, as a community pharmacist and have since progressed through various types of management to eventually land into the online pharmacy world.

Last reviewed: 22nd Oct 2026

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