“Fit” is a loaded word without a standard definition. Ask a doctor, and they’ll cite stats about metabolic health. Ask an athlete, and they’ll measure fitness by triathlon times and PRs. Ask a member of the fashion industry, and they’ll point to magazine covers and swimsuit models.

That’s why it’s no surprise that the question of whether you can actually be “fat and fit” is so hotly debated. Take, for example, the controversy over plus-size model Ashley Graham on the cover of Sports Illustrated’s iconic swimsuit issue or the technically obese NFL lineman Vince Wilfork holding his own in ESPN the Magazine’s body issue.

The debate isn’t confined to pop-culture magazine covers or social-media fat-shaming. There’s discord in the medical community as well about just how accurate static measures like body mass index are when it comes to giving a precise assessment of health.

So can you actually be both heavy and healthy? According to the experts and the latest research, the answer is technically yes — but there are some major caveats.

“It may sound cliché, but it’s literally what is on the inside that counts,” says Niket Sonpal, MD, assistant clinical professor at Touro College of Osteopathic Medicine in New York City. “Overall fitness is not just about the sheer numbers of weight-to-height ratio; it’s also about other factors like cardiovascular health, waist circumference, blood sugar levels, etc.”

As it stands, BMI, which is calculated by a ratio of height to weight, tends to be the go-to measure to classify someone as “fat” or not. But that ratio is a pretty narrow measure. It’s not at all unusual for an Olympic athlete or marathoner with a lot of muscle mass to fall into the “overweight” or even “obese” category, which is why a lot of medical professionals call bs on using BMI as an accurate measure of health. (Remember, muscle will up the number on the scale faster than added fat will.)

In fact, earlier this year, a study published in the Journal of the American Medical Association found that overall, the healthiest individuals — which were defined as individuals with the lowest early mortality rates — were actually those in the “overweight” BMI category. The study used data spanning four decades from over 100,000 participants and found that the BMI associated with the lowest risk of early mortality was 27. That’s squarely in the “overweight” category. In other words, they found that the “fat” people in the study were actually fitter than those of “normal” weight.

How is that possible? Sonpal says the measures of cardiovascular and metabolic health are the most important when it comes to determining an individual’s level of fitness. Those numbers will always trump the number on the scale. So if an “overweight” individual has stellar cardiovascular health, they might be considered fitter and healthier than a slimmer person who gets winded after running a mile.

“The way to measure if someone is truly ‘fit’ is through their blood pressure, resting heart rate, blood sugar, exercise tolerance, body fat percentage and other biomarkers to collectively assess health,” he says. “We need to look more at the functional ability as opposed to a static view. Your BMI is just a snapshot.”

This is largely why so many elite athletes dominate in competition despite a super high BMI. Call it the Vince Wilfork phenomenon.

“Athletes generally have a lower body-fat percentage — that is, more muscle — than the general population, says Alissa Rumsey, MS, RD , who specializes in sports nutrition. “An athlete’s weight may be higher, but most of that weight comes from muscle, as opposed to fat. In this case, BMI is not a good indicator of weight or health status.”

This isn’t a free pass to start packing on the pounds or adopting unhealthy eating habits. “Overweight is not synonymous with unhealthy,” says Sonpal. “But we do know that carrying a lot of weight puts stress on your joints and puts more stress on your metabolic health.” In reality, when you start gaining weight, your metabolic health will likely start declining.

So what’s the bottom line? You can technically be heavy and healthy. Body fat is a factor that weighs on overall fitness, but it is not the only factor. As Sonpal stresses, no single measure — whether that’s BMI or the number on the scale — can give you a full picture of health. So when it comes to setting health goals to achieve a greater level of fitness, make sure the focus is on what your body can accomplish rather than how it looks.