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: 

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 20^th 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.