The Obesity Paradox: How Fat Can Be Good for You

In 2005, a scientist at the US Centers for Disease Control and Prevention published findings that shook the health world to its core: Being "overweight" might be… good for you?

For years, doctors have believed that the more you weigh, the more unhealthy you are, and the higher your risk of disease and death. But this 2005 study found that people with body mass indexes in the overweight category were actually at lower risk of death than those with a "normal" BMI. This finding alone was surprising enough to land its author, Katherine Flegal, in a "firestorm" of controversy, despite her data being scientifically sound, per Boston Globe.

But Flegal wasn't the first researcher to find that weight may influence health in different ways than previously thought, nor would she be the last. The phenomenon that fat can offer certain protective health benefits is commonly called the "obesity paradox," a term that shows just how much it flies in the face of everything we thought we knew about fatness and health.

"The term 'obesity paradox' is a prime example of weight stigma in the scientific literature," Jeffrey Hunger, an assistant professor of social psychology at Miami University of Ohio told Scientific American in 2020. "Think about it: A paradox is something contradictory or seemingly absurd. This term came about because it was considered absurd that fat people could actually be healthy."

But the numbers don't lie. Fat people can be healthy and, in some cases, healthier than those who are thin. Here's what to know.

What is fat, anyway?

First, it's worth noting that measuring body size is more arbitrary than it might seem. BMI is used to define "normal," "overweight" and "obese" categories, but it's a flawed metric that was never intended to be used for individuals in the first place, let alone for every person of every background. Moreover, the categories have shifted over the years: in 1998, the National Institutes of Health abruptly moved the "overweight" and "obesity" cutoff points down to include 25 million more Americans. 

BMI also doesn't account for body composition: the ratio of body fat to muscle, bone and other tissues. Some doctors believe that "excess" body fat, especially belly fat, is the real health issue instead of weight -- having a high BMI isn't so much of an issue, they say, if the pounds are mostly muscle. 

But how much body fat is too much? Adipose tissue (the technical term for fat) is a crucial component of your bodily systems, from your immune system to your brain health. It stores energy and insulates the body in cold weather. It stores essential fat-soluble vitamins, including vitamins A, E, D and K, which is part of why fatty foods like avocados and nuts are now considered "healthy." And fat also affects your health in other, surprising ways.

Fat people are less likely to die from certain conditions

One of the main reasons that doctors discourage fatness is because higher BMIs are associated with a greater risk of chronic conditions like diabetes, heart disease and heart failure. But there's another important piece of the puzzle. Studies consistently find that overweight or obese individuals with these conditions are less likely to die from them than normal or underweight people, a sign that a high BMI offers some sort of protective effect -- another example of the obesity paradox.

As we age, being "moderately overweight" also seems to offer protection against developing multiple comorbid diseases, making it a "marker of a healthy aging process," according to a 2019 study in Italy. That's in line with Flegal's findings that overweight people live longer.

More fat = more muscle

Bigger people tend to be stronger than thin people, according to research, making them better at strength exercises such as weight lifting. That's because, in addition to having more fat tissue, they have more muscle mass, too. This is true for fat people of all ages, from youth to old age. 

Fat offers protection from injuries

Having a higher BMI also offers protection from injury in some cases. A 2020 study found that overweight and class I obese trauma patients had better chances of survival than patients with a "normal" BMI. In the past, researchers have also found that subcutaneous fat may help protect from injuries in car crashes in particular, and that overweight people had less severe injuries in a crash than thin people, though the research is mixed on this matter.

Fatness and fitness

It's clear that fat isn't the enemy, and can even be a perk in some cases. But bottom line: There's no need to be thinner or fatter in order to be healthy. You can be healthy at any size, while the reverse is also true: one study found that almost half of "overweight" people were metabolically healthy, while 30% of "normal" people were not.

Various studies have found that physical activity seems to matter more for health than BMI. In one 2017 study in the Netherlands, for example, people with high BMIs who were very physically active had the same likelihood of heart disease as people with normal BMIs who were just as active. 

Correlation doesn't equal causation. It's possible that the link between obesity and certain diseases has some other underlying reason. Rather than obesity causing disease, perhaps the two share a common, third cause, such as societal factors or diet. Weight stigma could also play a mediating role in predisposing fat people to illness. 

Centuries ago, having visible body fat was considered healthy; plumpness was the aspirational beauty standard, not thinness, as detailed in Sabrina Strings' book Fearing the Black Body: The Racial Origins of Fat Phobia. Not only do beauty and health values fluctuate over time, but the very definitions of fatness and thinness are moving goalposts. It's not surprising that being technically "overweight" or "obese" doesn't consistently translate to poorer health, and that yes, body fat has its benefits.