In a consensus statement published in the journal Obesity Reviews, experts from the World Obesity Federation make the case for defining obesity as a disease process. They argue that, by recognizing the primary agent as food rather than an infectious microbe, it fits a widely-accepted model of disease.

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The World Obesity Federation have classified obesity as a disease.

In their paper, Dr. G.A. Bray, from the Pennington Biomedical Research Center of Louisiana State University in Baton Rouge, and colleagues explain how their consensus statement follows a controversial debate that has been ongoing for a hundred years, and which has culminated in more and more medical bodies – including the American Medical Association – agreeing that obesity is a disease.

Since 1980, global obesity rates have more than doubled, and it has reached the point where most people live in countries where being overweight or obese is a bigger cause of death than being underweight.

To make their case for defining “obesity as a chronic progressive relapsing disease process,” Dr. Bray and colleagues use the “epidemiological model” of disease.

In the epidemiological model, there is “an environmental agent that acts on a host to produce a disease,” and the disease is “related to the virulence of the agent and the susceptibility of the host.”

The authors argue that food is the primary environmental agent for obesity. The typically Western diet is abundant in low-cost, tasty, and convenient foods that provide “pleasurable rewards from eating” by triggering the same parts in the brain – the “pleasure centers” – that are activated by addictive substances.

The authors also put forward the case for considering decline in physical activity as a second disease cause of obesity. The decline has happened at the same time as foods in the Western diet becoming cheaper and more abundant, providing a double driver of obesity.

As well as the two main agents – food and decline in physical activity – the authors note that various other environmental factors also contribute to increased obesity, including reduced sleep, some medications, endocrine disruptors, and older parental age.

Fast facts about obesity
  • More than one third of adults in the United States are obese.
  • Obesity is higher among middle-aged and older adults in the U.S.
  • In 2008, the average medical cost in the U.S. for an adult with obesity was $1,429 higher than for one of a normal weight.

Learn more about obesity

In discussing host-side factors, Dr. Bray and colleagues explain that more than 100 genes have been identified as risk factors for obesity, with some – such as those that cause defects in leptin – having a bigger effect than others.

Also, in people who are genetically predisposed to obesity, unused energy from food collects as excess fat in fat cells.

The authors argue that the fact that these fat cells get bigger or more numerous to store the excess energy are the pathological effects of the disease.

Another pathological effect of obesity, they suggest, is the increase in inflammation that results from the changes to fat cells interacting with the accompanying change in the composition of gut microbes.

Dr. Bray and colleagues conclude that while obesity is “a non-communicable disease process,” the epidemiological model that they describe of obesity shows that it has a “number of features in common with a ‘communicable disease’ including environmental agents, and the host responses to these agents.”

Dr. Bray says that an important reason for viewing obesity as a disease is that it draws attention away from patients being solely responsible for their condition and focuses it on how to tackle the disease process.

He also adds that “it shows that if we can successfully treat obesity, many of its associated diseases will be eliminated.”

In an accompanying comment letter, other experts highlight the arguments against classifying obesity as a disease, but eventually conclude that, on balance, the arguments in favor of such a decision outweigh them.

It could be argued, they note, that obesity should not be classed as a disease because it is “primarily a risk factor for other conditions rather than a disease in its own right.” Also, by “medicalizing” the condition, such a move effectively declares that a significant proportion of the population is “ill.”

They suggest that it could also fuel fears of an increased reliance on drugs and surgery and may reduce emphasis on tackling obesity through public health measures that address the fundamental social and commercial causes.

On the other hand, they say that defining obesity as a disease could help people who have it to access medical support as well as strengthen the call for action to deal with the social, environmental, and systemic causes of weight gain.

Such a move may also reduce the internalized stigma that affects some people with obesity, and alter the public view of who is to blame for the condition.

It could also change the attitude toward how to fund medical costs for obesity. For instance, in some countries, insurance schemes do not issue payments for conditions that are not classed as diseases. The experts conclude:

Whilst recognition of obesity as a disease has the potential to over-medicalize a problem of societal origins, it also has the potential to improve treatment access and outcomes and can serve to strengthen measures to reduce the obesogenicity of the environment to which the population is exposed.”

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