Is obesity a disease?

Everywhere you turn—from magazine covers in the supermarket checkout to news stories that pop up on your phone to this very article you’re reading—obesity and weight seem to be the center of the nation’s attention. 

As happens with any topic drawing the focus of millions of people, obesity has garnered quite a bit of debate and divisiveness. 

Is obesity a disease, or is it disrespectful or harmful to classify that way? Can you have obesity and still be healthy? To answer these questions, we have to understand obesity and its complexities. Let’s dive in.

Obesity is a technical definition based on a measurement called BMI (body mass index), a number that’s calculated based on your weight and height. There are all sorts of issues with BMI (we’ll get into those in a minute), but most healthcare providers and researchers still use this scale, which looks like this: 

Having a BMI of 30 or above would classify you as having obesity. For the most part, BMI does tell us a lot, which is why it’s still so widely used, but obesity is a lot more complicated than what BMI can measure. 

There are three primary issues with BMI, according to Dr. Tzvi Doron, an obesity medicine specialist. 

1. BMI doesn’t measure body fat

For one thing, Dr. Doron says, “BMI doesn’t directly measure how much fat a person has—it only tells you the relationship between weight and height.” This is important because adiposity—how much fat tissue a person is carrying—predicts a person’s health risks much more accurately than BMI alone.  

2. BMI doesn’t tell us where body fat is stored

A second, related issue with BMI is that it doesn’t give you the information you need about your metabolic risk. “People can have different risks at the same BMI,” says Dr. Doron, “which has to do with not just how much adiposity they have at a given BMI, but also where that fat is stored.” 

Visceral fat (fat around the organs and deep in the belly) is much more dangerous for health than subcutaneous fat (fat just under the skin). In general, the more fat you carry, the more of it will surround your organs. However, two people can carry the same amount of total fat, but that fat can be stored differently (with more or less around the organs vs. under the skin). How we store fat is largely determined by our genes.    

3. BMI isn’t helpful at the extremes of muscle mass

One of the major critiques of BMI is that it can overestimate or underestimate someone’s health risks if they’re carrying a lot or very little muscle. 

Says Dr. Doron, “In people who are heavily muscled, BMI will overestimate their body fat, while in people with ‘normal’ BMIs and very low muscle mass, BMI will underestimate their body fat.” 

For all its shortcomings, though, BMI is the most widely used standard used in studies, so the information we have is largely based on that. This brings us to our question…

Some may take issue with this, but yes, obesity is a disease. The World Health Organization (WHO) classified it as such in 1997, and the American Medical Association (AMA) followed suit in 2013. There’s been some pushback on these statements, but classifying obesity as a disease helps remove stigma and creates new opportunities for treatment. 

Obesity has all the features of a disease: 

• Chronic condition 

• Linked to a wide range of negative health outcomes

• Caused by a complex array of factors

While many see labeling it as a “disease” as a black mark against people with obesity, this couldn’t be further from the truth. 

If someone has a different chronic disease, like cancer, high blood pressure, or asthma, we don’t fault them for that or view them negatively because of it. We understand that diseases like these can happen for any number of reasons, including genetics, environment, lifestyle factors, completely unknown reasons—or any combination of these. Even when a person’s unhealthy lifestyle choices lead to chronic illnesses, such as COPD caused by smoking, we don’t view them negatively.

Obesity should be no different. 

Before labeling obesity as a disease, the default assumption was that it happened because people were ‘lazy’ or lacked self-control. These false and harmful ideas create stigmas around weight in society and make it harder for people to get the help they need because they create weight bias in the medical community. 

We now understand that obesity is a complex condition with many contributing factors, and it rarely has to do with people just not working hard enough. In fact, one large review study on nearly 50,000 people showed that over 40% of participants tried to lose weight over the study period. In other words, people are working hard to lose weight, but treating this condition isn’t just about putting in more work. 

As we’ll examine more closely below, obesity is linked to many other health conditions, including diabetes, heart disease, certain types of cancer, and more. So, it’s essential that people can get help—including medical treatment as necessary—and fighting against weight stigma is a big part of that. 

So, we know obesity is a disease, but where does it come from if not from simply “lacking self-control”, as many of us have been told countless times? It’s certainly not simple; let’s look at some of the possible causes: 

Genetics

Our genes play a huge role in our weight. We don’t even know just yet how big a role they play, but scientists have identified over 250 genes linked to obesity so far. 

If your parents or siblings have obesity, you’re more likely to develop it too—even from a young age. If your mother had obesity while pregnant with you, your chances of developing childhood or adolescent obesity increase dramatically. 

Of course, a genetic predisposition toward something doesn’t seal your fate, but it makes it a lot harder for you to avoid or prevent. When faced with the same environment and lifestyle that someone without that genetic predisposition faces, it will likely be more difficult for you to maintain a healthy weight. 

Environment

Obesity has only become a wide-scale issue relatively recently; today, about 42% of the US population has obesity, but up until the 1960s or so, this issue affected only a small percentage of the population. 

What caused this dramatic change? Many researchers believe that the environment we live in is largely responsible.

In recent years, we’ve become more sedentary as we spend more time in front of our TVs, binge-watching shows, and on our smartphones and laptops. Food science has advanced to make processed foods more delicious and harder to avoid, while advertisements make these foods more and more enticing. At the same time, portion sizes have increased. 

In other words, a LOT has changed in our environment. People who are genetically predisposed to develop obesity will do so at higher rates in the context of that environment. 

Lifestyle factors

The old advice to “just eat less and exercise more” is a harmful oversimplification of this disease. Still, the balance of calories-in/calories-out is a contributing factor to obesity. Our environment and genetics can play off each other to make it much harder to maintain a good balance of energy.

One of the major factors in defining obesity as a disease is understanding the health risks associated with obesity. It’s linked to a wide range of health conditions, including: 

• Cardiovascular events (like heart attack and stroke)

• Hypertension 

• Type 2 diabetes mellitus

• Digestive issues (like gallbladder disease and pancreatitis)

• Depression and anxiety

• Obstructive sleep apnea

• Pregnancy complications 

• Infertility

• Sexual dysfunction (like erectile dysfunction and low libido)

And those are just to name a few. Many studies have shown that obesity is linked to a 5–10 years lower life expectancy.

All of this highlights just how important it is to label obesity as what it is—a disease for which people need support and, in many cases, treatment. Obesity is a complex disease, and it’s not someone’s “fault” if they have it, any more than it would be their “fault” for having breast cancer or lupus. 

Understanding that is a first step in helping people mitigate and avoid many of these health risks. 

Effective treatments for obesity fall into three main buckets: 

• Lifestyle changes 

• Medications

• Surgery

Lifestyle changes

Changing your diet and increasing your physical activity can have a modest effect on weight loss, but the key is finding strategies that you can maintain long-term. What seems to work best is prioritizing minimally-processed foods and moderate-intensity exercise—in other words, avoiding extreme measures that likely won’t be sustainable. 

Weight loss medications

Many people are hesitant to entertain the idea of using medication to assist with weight loss, but when we understand that obesity is a disease, medical treatment makes more sense. You wouldn’t scoff at taking medication to control your blood pressure if lifestyle modifications don’t do the trick, and obesity should be no different.

Several safe and effective weight loss medications are now available, and they’ve helped millions of people lose weight and keep it off (along with lifestyle modifications). Most of these medications—including Saxenda and Wegovy—are part of a drug class called GLP-1s (glucagon-like peptide-1 receptor agonists). Other drugs approved for weight loss include Mounjaro and Contrave. 

Just like medications for other chronic diseases, people who get good results from these drugs need to stay on them long-term to continue seeing their weight loss effects. 

Surgery 

Weight loss surgery is the most invasive option, but for those who qualify, it’s one of the most effective treatments for obesity. Studies show that patients can lose 20–30% of their weight with bariatric surgery. 

Surgery for weight loss has also been shown to improve a wide range of health outcomes, including lowering risks for cancer, heart disease, gestational diabetes, depression, anxiety, and more. 

The other side of the “debate” around whether or not obesity should be classified as a disease is the assertion that plenty of people have obesity but are still “metabolically healthy.” Their bloodwork and other markers (like blood pressure) are within normal ranges, despite having excess weight. So, people on this side of the debate say we shouldn’t focus so much on weight, but just focus on people with metabolically unhealthy markers. 

“It’s a lot more complicated than that,” says Dr. Doron. “People can be metabolically healthy with an elevated BMI, but some research shows that this is usually temporary, while other research shows there may still be increased health risks even with metabolically healthy obesity.” 

Indeed, one extensive review study that included 4.5 million people showed that metabolically healthy people with overweight and obesity were still at increased risk for cardiovascular events (like heart attacks) and all-cause mortality (meaning, death from any cause). 

We’re still learning a lot about obesity, but we know that labeling it as a disease means we’re one step closer to getting past the stigmas around weight. We’re many steps closer to getting people the help they need to avoid the risks associated with excess weight.

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Current version

May 09, 2023

Written by

Rachel Honeyman

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.