Is Obesity a Disease?

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Please note: I don’t usually use the terms ‘obese’ or ‘overweight’ as these categories are flawed and often stigmatising. But I’ve had to use them in this article to address the topic in question and also when they have been used as categories within research.

The question of whether obesity is a disease is a hotly debated topic between different healthcare professionals and scientists.

Although this is gaining more attention recently, obesity was first defined as a disease by the International Classification of Diseases back in 1948. Today a number of countries and health organisations, including The World Health Organization (WHO) and the American Medical Association (AMA), already classify obesity as a disease (1).

So let’s take a look at what this really means and some arguments for and against this.

What Does ‘Obesity’ Mean?

‘Overweight’ and ‘obesity’ are defined by the World Health Organisation (WHO) as “…abnormal or excessive fat accumulation that presents a risk to health. A body mass index (BMI) over 25 is considered overweight, and over 30 is obese.” (2).

The obese BMI range is then subdivided into (3):

  • Obesity class I: BMI of 30 – 34.9
  • Obesity class II: BMI of 35 – 39.9
  • Obesity class III: 40 BMI of 40 and above

Waist circumference is also sometimes used along with or instead of BMI to estimate the amount of fat stored in the abdomen.

There are significant drawbacks to these measurements and definitions as discussed below.

How is ‘Disease’ Defined?

‘Disease’ can be tricky to define, but let’s take some dictionary definitions.

The Oxford dictionary defines this as: “a disorder of structure or function in a human, animal, or plant, especially one that produces specific symptoms or that affects a specific location and is not simply a direct result of physical injury.”.

The Merriam-Webster dictionary defines disease as “an illness that affects a person, animal, or plant: a condition that prevents the body or mind from working normally.” (4).

Why Define Obesity as a Disease?

Those who feel that obesity is a disease often state that this has been mistakenly treated as a lifestyle choice, that can be reversed via willpower (1).

This acknowledges that body shape and size are influenced by a complex web of factors including genetics, metabolism, environment, movement, education, financial situation, other medical conditions and medication.

So the argument is sometimes put forward that treating obesity as a disease involves less blame and is less stigmatising (1).

Supporters of this argument also often highlight health issues that can be associated with a higher fat mass, such as heart disease, certain types of cancer and type 2 diabetes.

Some people also feel that treating obesity as a disease can help to focus research and funding towards the treatment of this, using stepped-up options from the typical ‘healthy diet and lifestyle’ advice, such as bariatric surgery, weight loss medication and very low-calorie diets.

Arguments Against Defining Obesity as a Disease

There are a number of different arguments against calling obesity a disease.

There’s Currently No Reliable Way To Define Obesity

BMI is notoriously inaccurate on an individual level.

Even WHO states that BMI “is not perfect because it is only dependant on height and weight and it does not take into consideration different levels of adiposity based on age, physical activity levels and sex. For this reason, it is expected that it overestimates adiposity in some cases and underestimates it in others” (3).

WHO also states that “association between waist circumference and health risks is not an easy task and should be done scientifically using proper techniques” (3).

A Higher BMI or Fat Mass Doesn’t Always Lead to Worsened Health

Then if we look at the above definitions of ‘disease’ these state that “specific symptoms” must occur or this must “[prevent] the body or mind from working normally”. This simply isn’t the case for a lot of people who meet the definition for ‘obesity’.

Let’s look at some evidence-based examples:

  • Population-based studies have found that those in the ‘overweight’ BMI category of 25-30 actually have the lowest risk of mortality and chronic disease (5).  
  • A large study from 2014 found that those those who were fit and in the ‘overweight’ or ‘obese’ BMI categories had a similar risk of death as those in the ‘normal’ BMI category (6).
  • For those who are considered ‘metabolically unhealthy’ (i.e. higher cholesterol, blood pressure or glucose levels) a lower risk of heart issues has been found in those in the ‘overweight’ or ‘obese’ categories as comapred with the ‘normal’ range (6).
  • Many aaspects of health can improve as a result of making healthy chocies, like moving more, better sleep or managng stress, even when weight doesn’t change (7-8).

Of course, there can be health issues related to having a bigger body, but being in a bigger body doesn’t inherently mean worsened health.

It can also be difficult to tease out how much of certain size-related related issues are linked with factors like weight stigma and weight cycling, as these aren’t always taken into account in weight-related research.

Labelling a Body Type as a ‘Disease’ Is Stigmatising

Labelling a bigger body as a disease is considered fatphobic by many people.

This suggests that there is something wrong with living in a bigger body, or that this inherently needs to be treated or fixed. Even though a person in a bigger body can be fit and healthy (as discussed above).

The words ‘overweight’ and ‘obesity’ are also often seen as stigmatising and medicalising body types.

There’s a risk that viewing obesity as a disease may worsen the weight stigma already faced by those in a bigger body. For example, would this need to be declared to an employer or potential employer as a disease, even if body size isn’t impacting a person’s health or ability to work?

Weight stigma in itself can cause real harm.

Weight stigma has been seen to worsen both physical and mental health and worringly can lead to avoidance of medical settings (9-11).

Pursuing Weight Loss Can Be Harmful

Calling obesity a disease also suggests that this needs to be treated, and weight loss treatments often come with significant risks.

For example, trying to lose weight has been linked with (7-8):

  • Reduced health behaviours
  • Lower self-esteem
  • Worsened body image
  • Increased risk of disordered eating
  • Cycles of losing and regaining weight

Importantly, there’s currently no good evidence that the majority of people can lose weight and keep this off in the long term using diet and exercise.

In fact, most people have been seen to regain weight within five years, and more than half of people may regain more than they originally lost (7-8, 12-13).

Weight loss medication and surgery can also increase certain medical and psychological risks or lead to unpleasant side effects.

For more information about the issues with weight-focused healthcare check out this article.

How Helpful Is It To Define Obesity As a Disease?

Most people on both sides of this argument agree that body shape and size is complex, and influenced by numerous factors, many of which are beyond our control — therefore body size isn’t an individual choice or merely down to willpower.

Both sides also tend to agree that weight stigma is wrong and harmful. Although this differs where framing obesity as a disease is seen as being less stigmatising by some people, and more stigmatising by others.

Both camps also usually see the current limitations and issues with defining ‘obesity’ in a reliable way. But there is a big difference in the way that some people see ‘obesity’ as something that needs to be changed and treated.

Based on my experience and understanding of what a disease is and the evidence related to this topic, I feel that classifying ‘obesity’ as a disease is more likely to be stigmatising and unhelpful.

But when we compare these pros and cons, we really need to take it back to the individuals this will impact the most. People living in bigger bodies will have different opinions about this topic of course, so it’s vital that their experiences are placed in the centre of this debate. It would also be helpful if research was conducted to examine the real-life implications of framing ‘obesity’ as a disease.

If you would like to read more about alternative options to focusing on weight and weight loss, check out this article on weight-inclusive healthcare.


  1. Burki (2021) “European Commission classifies obesity as a chronic disease” [accessed Feb 2022 via:
  2. WHO “Obesity” [accessed Feb 2022 via:]
  3. WHO “Body mass index – BMI” [accessed Feb 2022 via:]
  4. [accessed Feb 2022 via:]
  5. Flegal, K.M., Kit, B.K., Orpana, H. and Graubard, B.I., 2013. Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. Jama, 309(1), pp.71-82. [accessed Feb 2022 via:]
  6. Barry, V.W., Baruth, M., Beets, M.W., Durstine, J.L., Liu, J. and Blair, S.N., 2014. Fitness vs. fatness on all-cause mortality: a meta-analysis. Progress in cardiovascular diseases, 56(4), pp.382-390. [accessed Feb 2022 via:]
  7. Bacon, L. and Aphramor, L., 2011. Weight science: evaluating the evidence for a paradigm shift. Nutrition journal, 10(1), pp.1-13. [accessed Feb 2022 via:]
  8. Sturgiss, E., Jay, M., Campbell-Scherer, D. and van Weel, C., 2017. Challenging assumptions in obesity research. Bmj, 359. [accessed Feb 2022 via:]
  9. Vadiveloo, M. and Mattei, J., 2017. Perceived weight discrimination and 10-year risk of allostatic load among US adults. Annals of Behavioral Medicine, 51(1), pp.94-104. [accessed Feb 2022 via:]
  10. Chen, E.Y., Bocchieri-Ricciardi, L.E., Munoz, D., Fischer, S., Katterman, S., Roehrig, M., Dymek-Valentine, M., Alverdy, J.C. and Le Grange, D., 2007. Depressed mood in class III obesity predicted by weight-related stigma. Obesity Surgery, 17(5), pp.669-671. [accessed Feb 2022 via:]
  11. Phelan, S.M., Burgess, D.J., Yeazel, M.W., Hellerstedt, W.L., Griffin, J.M. and van Ryn, M., 2015. Impact of weight bias and stigma on quality of care and outcomes for patients with obesity. obesity reviews, 16(4), pp.319-326. [accessed Feb 2022 via:]
  12. Fildes, A., Charlton, J., Rudisill, C., Littlejohns, P., Prevost, A.T. and Gulliford, M.C., 2015. Probability of an obese person attaining normal body weight: cohort study using electronic health records. American journal of public health, 105(9), pp.e54-e59. [accessed Feb 2022 via:]
  13. Mann, T., Tomiyama, A.J., Westling, E., Lew, A.M., Samuels, B. and Chatman, J., 2007. Medicare’s search for effective obesity treatments: diets are not the answer. American Psychologist, 62(3), p.220. [accessed Feb 2022 via:]


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