Is Obesity A Disease? Why Obesity Is Recognised As A Chronic Condition

If you live with obesity, you've probably heard mixed messages about what it actually is. Some people still believe weight management is a matter of willpower. Health experts increasingly call it a disease. This mix of messages can make it hard to know where you stand, or what kind of support might help you.

This article looks at what the evidence says, and what it means for you. It draws on guidance from the NHS, the World Health Organisation and peer-reviewed research, plus advice on weight loss at the bottom of this page.

Article Summary:

• Obesity is a long-term health condition linked to a higher risk of other illnesses. Weight management isn't simply a matter of willpower.
• The World Health Organisation has classed obesity as a chronic disease since 1997, though the UK hasn't given it this formal status yet.
• New medical guidance now splits obesity into two types, "preclinical" and "clinical", based on how it affects your body.

What do doctors mean by "obesity"?

Obesity means carrying more body fat than is healthy for you. Doctors usually check for it using a measurement called body mass index, or BMI. This compares your weight to your height. A BMI of 30 or above generally falls into the obesity range, but the threshold is lower if you're from a South Asian, Chinese, Middle Eastern, Black African or African-Caribbean background, because health risks can start at a lower weight for these groups. [1]

Using BMI as an indicator has its limitations. It can't tell the difference between fat and muscle, and it doesn't show your body fat percentage or where that fat is stored. This is why it's often used alongside other measurements, such as your waist size, to build a fuller picture of your health. [1]

Around 1 in 4 adults in the UK are living with obesity. [1] If you're one of them, you're far from alone, and there's support available to help you.

Is obesity officially a disease?

This depends on where you look. The World Health Organisation (WHO) has classed obesity as a chronic, complex disease since 1997. [2] In the UK, the picture is different. The NHS currently describes obesity as a chronic health condition rather than a disease. [1]

In 2019, the Royal College of Physicians called on the UK government to formally recognise obesity as a disease. [3] Their argument was that giving obesity this status would help reduce the stigma around it and support better access to treatment, care, and long-term funding. Despite this decision, the UK still hasn't given obesity this official legal status. [4]

What both sides agree on is this: obesity isn't caused by a lack of willpower. It develops through a mix of genetics, health conditions, hormones, and the environment you live in, and it deserves the same medical attention as any other long-term condition.

New ways to understand obesity

In 2025, a group of international experts, brought together by the Lancet Diabetes & Endocrinology Commission, published new guidance that moves the conversation forward. [5] They split obesity into two categories:

• Preclinical obesity means you're carrying excess body fat that's a risk factor for future health problems, but your organs are still working normally, so you're not currently unwell because of it.
• Clinical obesity means the excess fat has started to affect how your body functions. This might show up as breathlessness, ongoing joint pain, or other signs that your organs are under strain.

To make this distinction, doctors are being encouraged to look beyond weight and height. This can include measuring your waist-to-hip ratio, or checking for visceral fat, the fat stored around your organs, which carries a higher health risk than fat stored elsewhere on your body. [5]

Under this new approach, clinical obesity is treated as a disease in its own right. Preclinical obesity is treated as a risk factor that's worth monitoring and managing early, before it develops further. [5]

The Royal College of Physicians has endorsed this new framework, saying it offers a more accurate and less stigmatising way to understand what's happening in your body, rather than relying on BMI alone. [6]

Why the label matters

It might seem like a technical debate, but how obesity is classified has a real effect on people's lives. If a health condition is recognised as a disease, it can lead to clearer treatment pathways, more consistent research, and better support for individuals.

Framing obesity as a disease also shifts the focus away from appearance and towards health. It recognises that your weight is shaped by many things outside your control, including your genes, your environment, and other health conditions, not just what you eat or how much you move.

What causes obesity?

Obesity usually develops when your body takes in more energy from food and drink than it uses. Several things can make this more likely, including:

• Low physical activity.
• Eating and drinking more calories than your body needs, especially foods high in fat and sugar.
• Certain health conditions, such as an underactive thyroid.
• Some medicines, including certain steroids and antidepressants.
• Your genes, which can affect how your body stores fat.
• Getting older, or going through the menopause or perimenopause.
• Social pressures and the environment you live in, such as easy access to high calorie food.

If you have an eating disorder or a mental health condition like depression, this can also make it harder to maintain a healthy weight. [1]

The health risks linked with obesity

Living with obesity raises your risk of developing several other health conditions, including:

• Type 2 diabetes
• Heart disease and stroke
• High blood pressure
• Some cancers, including breast, womb and bowel cancer
• Osteoarthritis
• Fatty liver disease

It can also lead to day-to-day problems like breathlessness, joint pain, poor sleep, low energy levels, and low mood. On average, living with obesity is linked to a shorter life expectancy of between 2 and 10 years. [1]

The encouraging news is that losing just 5 to 10% of your body weight can meaningfully improve your health, even if you don't reach what's considered a "healthy" BMI. [1] You can read more in our guide to common weight loss questions.

How is obesity treated?

Treatment usually starts with support to change your diet and physical activity levels, alongside help for any underlying health conditions. If you need more support, a GP may be able to refer you to a weight management programme, which might include coaching, group support, or structured eating plans. For more complex needs, you may be referred to a specialist weight management service with its own support team. [1]

For some people, weight loss medication can help. GLP-1 and GIP receptor agonists, such as semaglutide and tirzepatide, work by copying a hormone your body releases after eating. This helps you feel fuller for longer and reduces your appetite, and can help you lose weight when paired with a healthy diet and exercise. You can find out more about how these work in our guide to GLP-1 weight loss injections. Researchers are also exploring newer approaches, including peptides for weight loss, which target similar pathways in the body.

Weight loss medication is typically available for people with a BMI in the 'obese' range (30 or higher), but it can also be prescribed at lower BMIs if you have a weight-related condition like type 2 diabetes, heart disease, or fatty liver disease.

Weight loss surgery is another option for some people, usually if other treatments haven't worked and your BMI is above a certain threshold. [1]

New treatments and diagnostic tools are being tested all the time. If you're interested in the evidence behind current and emerging treatments, our page on weight loss clinical trials covers this in more detail, as does our look at the future of obesity treatments.

What this means for you

Obesity isn't yet officially classed as a disease in the UK, though the WHO has recognised it as one since 1997, and UK experts continue to call for change. New research is reshaping how doctors understand and diagnose it, moving beyond BMI to look at how excess fat actually affects your body. However it's labelled, obesity is a genuine health condition, shaped by biology and environment, and it responds to the right support.

Whatever label ends up being used, obesity is a health condition that deserves proper care, not judgement. If you're living with obesity and thinking about your options, it's worth having an open conversation with a GP, pharmacist, or a regulated online clinic about what support could work for you.

At MedExpress, we provide online consultations with regular clinical check-ins, and a range of weight loss treatments including Mounjaro Pen, Wegovy Pen, Wegovy Pill and Foundayo and our team can help you find the right treatment for you.

References

1. NHS. Overweight and obesity in adults [Internet]. NHS; 2026 [cited 2026 Sep 2]. Available from: https://www.nhs.uk/conditions/overweight-and-obesity/
2. World Health Organisation. Obesity and overweight [Internet]. Geneva: WHO; 2025 [cited 2026 Sep 2]. Available from: https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
3. Royal College of Physicians. Recognising obesity as a disease would help people manage their condition [Internet]. London: RCP; 2019 [cited 2026 Sep 2]. Available from: https://www.rcp.ac.uk/news-and-media/news-and-opinion/recognising-obesity-as-a-disease-would-help-people-manage-their-condition/
4. Luli M, Yeo G, Farrell E, et al. The implications of defining obesity as a disease: a report from the Association for the Study of Obesity 2021 annual conference. eClinicalMedicine. 2023;58:101962. Available from: https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00139-6/fulltext
5. Rubino F, Cummings DE, Eckel RH, et al. Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 2025 Mar;13(3):221-262. Available from: https://pubmed.ncbi.nlm.nih.gov/39824205/
6. Royal College of Physicians. Royal College of Physicians endorses Lancet definition and diagnostic criteria for obesity [Internet]. London: RCP; 2025 [cited 2026 Sep 2]. Available from: https://www.rcp.ac.uk/news-and-media/news-and-opinion/royal-college-of-physicians-endorses-lancet-definition-and-diagnostic-criteria-for-obesity/