Go to the page content
About obesity

Has obesity always been classified as a disease and why are prevalence rates on the rise?

In recent years, worldwide news headlines have been dominated by stories about the rapid rise in rates of obesity, which is now classified as a disease. This has led some people to question why obesity is defined as a disease when rates are increasing exponentially. What has changed? To understand why rates of obesity are soaring, we need to first understand what causes it and why it is defined as a disease.

5 min. read
Woman speaking to doctor

The image is a model

Defining obesity as a disease

In 2013, the American Medical Association followed the lead of several other notable organisations, and officially recognised obesity as a disease. The recognition identified obesity as a health condition with ‘multiple pathophysiological aspects’. In simpler terms, obesity is significantly more complex than simply ‘eating less and moving more’.

Let’s start with a key question. Why was obesity classified as a disease? Like diabetes, it meets the common criteria of a disease. It has characteristic signs or symptoms (i.e. an increase in body fat), it increases the risk of other diseases (e.g. diabetes and cardiovascular disease), and it prevents the body from functioning normally, by disrupting energy levels.

Despite this, there is still some resistance towards the idea that obesity is anything more than a ‘lifestyle’ issue. It is interesting to note that the concept of obesity as a disease has existed for many centuries – even dating as far back as the time of Hippocrates! In particular, the literature of the 17th and 18th century recognised the impact of lifestyle factors: “[Obesity] may be ranked amongst the diseases arriving from original imperfections in the functions of some of the organs, yet it must be admitted also, to be most intimately connected with our habits of life," Thomas Sydenham, 1624–1689.

The rise in obesity globally is one of the reasons that many people question the validity of obesity as a disease. This is despite the fact that there are examples of other diseases around the world that have increasing prevalence rates. For example, the rates of Inflammatory Bowel Disease (IBD) are increasing globally, particularly in lower income regions, with little scientific debate about the status of IBD as a disease.

Perhaps then, it is important to tackle the question: 

If obesity is, and has always been, a disease – why are prevalence rates rising now?

The statistics make for sobering reading. Latest predictions show that by 2030, over 1.5 billion people will live with obesity. Worldwide obesity has nearly tripled since 1975, and rates are predicted to rise exponentially, doubling between the years of 2020 and 2035.

To understand what is fuelling the rise in obesity, we must first understand the diverse and complex factors that cause it. Many people believe that weight loss can be achieved simply by ‘eating less and moving more’. The reality is far more nuanced. While diet and levels of activity undoubtedly play a role in maintaining healthy weight levels, there are many other factors that impact on the potential to develop obesity. These include hereditary factors – genetics, family history, racial/ethnic differences and social pressures – all of which play a role in determining whether a person is likely to develop obesity.

So, what has changed? Quite simply, our world and the way in which we live are being transformed. Profound social and economic shifts have taken place since the early 20th century, many of which could be described as ‘obesogenic’, i.e. they favour the development of obesity.

Changes to our diet and daily habits are a key factor in the rising levels of obesity. For example, there is now widespread access to energy-dense foods that are high in fats and sugars and these are often available at a lower cost than foods of higher nutritional value. It is important to reiterate the fact that no one should be stigmatised or blamed for eating what is often termed ‘junk’ food. For many people, it is the most accessible and affordable option, and packaging and food labelling can be misleading in terms of the true contents of processed food. Socio-economic factors play a key role. Many people simply cannot afford to buy and prepare nutritious food or have poor knowledge of cooking or nutrition.

Other lifestyle factors can influence our propensity to develop obesity. Nowadays, many people lead a much more sedentary life than their ancestors – they are generally far less active. Reasons for this include lack of access to sporting or recreational facilities, the widespread use of mechanised transportation and increasing urbanisation. Low levels of activity can tip the balance in the favour of obesity. 

Environmental factors also play a part. Exposure to specific chemicals can lead to neurochemical or hormonal imbalances that can affect the way in which we respond to food and increase the risk of developing obesity.

All of these factors are implicated in fuelling the rise in obesity. The truth is that obesity is, and has always been, a disease, just like diabetes. The chances of developing it vary from person to person depending on a complex interaction of multiple factors. Genetic factors play a role but external influences and lifestyle choices are also key. Specific elements of the changing world we live in can ‘trigger’ obesity or at least increase the chances of developing it in people who are pre-disposed to developing overweight. This certainly does not mean that becoming overweight is inevitable – greater awareness of the multiple factors affecting obesity can allow us to make smarter choices about how we live.

  1. Twells LK, Janssen I, Kuk JL. Canadian Adult Obesity Clinical Practice Guidelines: Epidemiology of Adult Obesity. Available from: https://obesitycanada.ca/guidelines/epidemiology. Accessed March 2024
  2. Rosen, H. 2014.  Is Obesity A Disease or A Behavior Abnormality͍ Did the AMA Get It Right͍. Missouri Medicine. 104. 111(2)
  3. Kyle TK, Dhurandhar EJ, Allison DB. Regarding Obesity as a Disease: Evolving Policies and Their Implications. Endocrinol Metab Clin North Am. 2016 Sep;45(3):511-20. doi: 10.1016/j.ecl.2016.04.004. PMID: 27519127; PMCID: PMC4988332.
  4. De Lorenzo, A., Gratteri, S., Gualtieri, P. et al. Why primary obesity is a disease?. J Transl Med 17, 169 (2019). https://doi.org/10.1186/s12967-019-1919-y
  5. Wang, R. et al. (2023) ‘Global, regional and national burden of inflammatory bowel disease in 204 countries and territories from 1990 to 2019: A systematic analysis based on the global burden of disease study 2019’, BMJ Open, 13(3). doi:10.1136/bmjopen-2022-065186.
  6. World Obesity. World Obesity Atlas 2023. Available at: 1.        https://www.worldobesity.org/resources/resource-library/world-obesity-atlas-2023. Accessed: February 2024
  7. Obesity and overweight (2021) World Health Organization. Available at: https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight. Accessed March 2024
  8. Hruby A, Hu FB. The Epidemiology of Obesity: A Big Picture. Pharmacoeconomics. 2015 Jul;33(7):673-89. doi: 10.1007/s40273-014-0243-x. PMID: 25471927; PMCID: PMC4859313.
  9. Blackshaw, J., Ewins, M. and Chang, M. (2019) Health matters: Addressing the food environment as part of a local whole systems approach to obesity, UK Health Security Agency. Available at: https://ukhsa.blog.gov.uk/2019/08/08/health-matters-addressing-the-food-environment-as-part-of-a-local-whole-systems-approach-to-obesity/. Accessed March 2024
  10. Darbre PD. Endocrine Disruptors and Obesity. Curr Obes Rep. 2017 Mar;6(1):18-27. doi: 10.1007/s13679-017-0240-4. PMID: 28205155; PMCID: PMC5359373.


Was this valuable for you?

You might also like