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Obesity is a complicated public health issue that medical experts are now acknowledging has multiple factors. These include physical, psychological, and genetic causes.

We’ll define obesity as medical experts currently do. We’ll also review statements and debate from the medical community about whether people should view obesity as a disease.

Major medical organizations consider obesity a disease, while some medical professionals disagree. Here’s why.

Doctors consider obesity to be a condition in which a person develops excess body fat, also known as adipose tissue. Sometimes doctors may use the term “adiposity.” This term describes the state of excess fat tissue in the body.

Carrying this extra fat can cause health complications, including type 2 diabetes mellitus, high blood pressure, and coronary heart disease.

Doctors use measurements like body weight, body height, and body build to define obesity. Some of the measurements include:

Body mass index

The body mass index (BMI) calculation is weight in pounds divided by height in inches squared, multiplied by 703, which is used to convert the measurement to the unit of BMI in kg/m2.

For example, a person who is 5 feet, 6 inches tall and 150 pounds would have a BMI of 24.2 kg/m2.

The American Society for Metabolic and Bariatric Surgery defines three classes of obesity based on range of BMI:

  • class I obesity: a BMI of 30 to 34.9
  • class II obesity, or serious obesity: a BMI of 35 to 39.9
  • class III obesity, or severe obesity: a BMI of 40 and higher

A BMI calculator like the one provided by the Centers for Disease Control and Prevention (CDC) or by Diabetes Canada can be a place to start, though BMI alone doesn’t necessarily say what’s healthy for each person.

Waist circumference

Having a larger amount of abdominal fat relative to the rest of the body causes a greater risk of health complications. So a person may have a BMI that is in the “overweight” range (the category before obese), yet doctors consider them to have central obesity due to their waist circumference.

You can find your waist circumference by measuring your waist just above your hipbones. According to the CDC, a person is at greater risk for obesity-related conditions when their waist circumference is more than 40 inches for a man and 35 inches for a nonpregnant woman.

Measurements like BMI and waist circumference are estimates of the amount of fat a person has. They aren’t perfect.

For example, some bodybuilders and performance athletes may be so muscular that they have a BMI that falls in the obese range.

Most doctors will use BMI to make their best estimate about obesity in a person, but this may not be accurate for everyone.

After measurements defining obesity, doctors must consider what the term “disease” means. This has proven difficult as far as obesity is concerned.

For instance, a 2008 commission of experts from The Obesity Society attempted to define “disease.” They concluded the term is too complicated to be fully defined. Unlike scientific measurements that have an equation and numbers behind them, “disease” can’t have as much of a cut-and-dry definition.

Even a dictionary definition doesn’t clarify the term beyond the general. For example, here’s the one in Merriam-Webster’s:

“A condition of the living animal or plant body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms.”

What doctors do know is there is a difference in how the public, insurance companies, and various health institutions view a condition that many see as a disease versus one that isn’t.

In 2013, American Medical Association (AMA) House of Delegates members voted at their annual conference to define obesity as a disease. The decision was somewhat controversial because it went against the recommendations of the AMA’s Council on Science and Public Health.

The council had researched the topic and didn’t recommend that the delegates define obesity as a disease. However, the delegates made their recommendations because there aren’t reliable and conclusive ways to measure obesity.

The AMA’s decision sparked what is a continued debate on the complexity of obesity, including how to most effectively treat it.

Years of research have led doctors to conclude that obesity is a health condition that’s more than a “calories-in, calories-out” concept.

For example, doctors have found some genes may increase a person’s hunger levels, which leads them to eat more food. This can contribute to obesity.

Also, other medical diseases or disorders can cause a person to gain weight. Examples include:

Taking certain medications for other health conditions can also lead to weight gain. Examples include some antidepressants.

Doctors also know that two people who are the same height can eat the same diet, and one may be obese while the other isn’t. This is due to factors such as a person’s base metabolic rate (how many calories their body burns at rest) and other health factors.

The AMA isn’t the only organization that recognizes obesity as a disease. Others that do include:

Not all medical experts agree with the AMA. These are just a few of the reasons some may reject the idea that obesity is a disease, given the current methods available for measuring obesity and its symptoms:

There’s no clear way to measure obesity. Because the body mass index doesn’t apply to everyone, such as endurance athletes and weightlifters, doctors can’t always use BMI to define obesity.

Obesity doesn’t always reflect poor health. Obesity can be a risk factor for other medical conditions, but it doesn’t guarantee a person will have health problems.

Some doctors don’t like calling obesity a disease because obesity doesn’t always cause negative health effects.

A number of factors influence obesity, some of which can’t be controlled. While eating choices and physical activity level can play a role, so can genetics.

Some medical experts express concern that calling obesity a disease can “foster a culture of personal irresponsibility.” Because doctors often want their patients to take an active role in their health, some worry classifying obesity as a disease may affect how people treat their health or think of their options and their abilities.

Defining obesity as a disease may increase discrimination for those with obesity. Some groups, such as the Fat Acceptance at Every Size movement and the International Size Acceptance Association, have expressed concern that defining obesity as a disease allows others to further separate and classify persons as obese.

Obesity is a complicated and emotional issue for many people. Researchers know there are many factors at play, including genetics, lifestyle, psychology, environment, and more.

Some aspects of obesity are preventable — a person can ideally make changes to their diet and exercise routine to build and maintain their heart health, lung capacity, range and speed of motion, and comfort.

However, doctors know that some people make these changes, yet still are unable to lose significant amounts of weight.

For these reasons, the debate over obesity as a disease will likely continue until other methods for numerically and reliably determining obesity emerge.