'You wouldn’t tell someone with asthma to work harder with their breathing': why obesity should be recognised as a disease

The idea that obesity is a disease is not new:

‘Corpulency, when in an extraordinary degree, may be reckoned as a disease, as it in some measure obstructs the free exercise of the animal functions; and hath a tendency to shorten life, by paving the way to dangerous distempers’

(Flemyng, 1757).[1]

Obesity develops over time when energy intake exceeds energy expenditure. Most excess energy in the body is stored as fat. When fat accumulates in the body it can limit mobility and put extra strain on joints, some of the excess fat may ‘spill over’ into other organs such as liver, muscle and pancreas, causing metabolic problems such as diabetes and fatty liver disease.

All of the known rare single gene variants leading to obesity do so by influencing the regulation of food intake. Most people with obesity are likely to have multiple variants with lesser individual effects, which makes them more likely to eat more. The amount of extra food is too small for most people to notice on a daily basis, but leads to obesity over many years. 

It is also very hard to lose weight because the body responds to weight loss by changing the balance of gut hormones and neural signals to make us feel hungry; at the same time the body conserves energy by slowing metabolism. These signals may be stronger in people with obesity, making it even harder for them to lose weight and keep it off.[2]

We now have extensive evidence from multiple epidemiological studies that obesity is associated with many complications which may be mechanical (the physical effects of the excess weight such as arthritis or sleep apnoea), metabolic (including type 2 diabetes, fatty liver, cardiovascular disease, and increased risk for some cancers) and mental (depression, anxiety, the effects of stigma). These complications are more likely to occur in the heaviest people and on average shorten life by about 12 years in those with severe obesity. So should obesity be classified as a disease? Let’s consider the arguments for and against.

Arguments for classifying obesity as a disease:

• Like many diseases obesity has genetic / epigenetic and environmental / social components
• Obesity results in poor health and early mortality
• Considering people with obesity has having a disease may help remove stigma. There is now compelling evidence from trials and observational studies that reducing excess weight ameliorates some of the adverse consequences (eg diabetes, cardiovascular disease and cancer).
• Effective treatments are available – these include lifestyle interventions, drugs and bariatric surgery

Arguments against classifying obesity as a disease:

• Concerns about labelling high proportion of population as diseased
• Healthy Obesity – not everyone who meets criteria is ill
• Could be perceived as removing personal responsibility
• Stigmatisation may occur as a result of the disease label.

Refutation of arguments against

• The current definition is based largely on BMI and there is increasingly recognition that this is imperfect. Whilst ongoing scientific dialogue may eventually result in refinement of definition (which may differ depending on ethnicity), this does not mean the condition is not a disease.  This process has happened for many other diseases such as diabetes and hypertension where definitions and thresholds for treatment have changed, yet all are accepted as diseases
• Longitudinal studies show that ‘healthy obesity’ is largely a transient state, with most individuals going on to develop complications
• The personal responsibility argument reflects blame back to the person with obesity. This is incorrect as it fails to recognise the powerful genetic and environmental pressures that are the cause of obesity in the first place, that also make it very difficult for people to lose weight and keep it off.  People with other diseases that everyone accepts are not caused by making ‘bad’ life choices (for example type 1 diabetes) still have to take some personal responsibility to help manage their condition (and will most likely have better outcomes if they do), but that does not mean that it is their fault that the condition has developed. Likewise other conditions where there is clearly a lifestyle component such as COPD or lung cancer in a person who smokes, are still recognised as diseases.
• Stigmatisation occurs because of an attitude prevalent in society that people with obesity are somehow ‘weak willed’ or have made poor lifestyle choices. The evidence discussed above clearly shows that this is not true. In contrast, people with obesity say that treating them has having a disease will help remove stigma.  Hence there is a need to change the language used as recently argued by the World Obesity Federation.[3]

In summary, recognising obesity as a complex, relapsing disease with severe health consequences should help to focus attention on the need to provide comprehensive policies that aim to reduce the development of obesity in those at risk, and provide evidence-based effective treatments for those who have already developed obesity, rather than exhorting them to ‘try harder’. 

If that approach was used for people who had (for example) asthma (‘you need to work harder at your breathing’) or cancer cachexia (‘eat more’), or those with depressive illness to (‘be happier’ or ‘pull themselves together’) it would be quite rightly considered inappropriate advice, but that is exactly what those who advocate the approach that people with obesity should be simply eating less and moving more are saying.  It is far more complicated than that.

Professor John Wilding leads clinical research into obesity at the University of Liverpool and specialist services for severe obesity at University Hospital Aintree and is president-elect of the World Obesity Federation.