You’re familiar with body mass index (BMI), right? That’s the number your doctor gives you after a visit to determine whether you’re overweight or obese. It’s a simple calculation—you can find your number here—that’s based on just your height and your weight.
A number between 18.5 to 24.9 is considered ideal—that’s normal weight. Overweight is 25 to 29.9, and obese is anything above that.
Sounds simple, right? Well, it might be too simple. Just because your BMI falls within the normal range doesn’t guarantee that you’re in the clear. You could still be “skinny fat.”
You might’ve heard the term used to describe someone who looks flabby, but not big enough to seem overweight. But it’s not just about appearances—it’s linked to some serious health issues.
Around 20 percent of people who are normal weight are “overfat”—where their BMI is normal but they are considered metabolically obese, a study in Hormone and Metabolic Research found. In normal-weight people, it’s often due to excess abdominal fat, which can put them at risk of a whole host of health issues.
And many people who are “overfat” don’t even know it. “BMI tests miss more than half of people who have unhealthy levels of excess body fat,” says Philip Maffetone, Ph.D., an independent exercise physiology and nutrition researcher who first coined the term “overfat” in 1977.
That could put overfat people at risk for serious health issues. Here’s what you should know about what people consider “skinny fat,” and how to tell if your body fat levels are where they should be.
Skinny fat doesn’t just mean flabby.
It means that your body fat percentage is too high relative to your lean muscle mass. So it’s more a ratio—not just a number in general, like your weight. Some experts think “overfat” should be used instead of terms like “overweight” or “obese,” according to a recent Frontiers in Public Health study by Maffetone and his colleagues.
“The thing that people get tripped up on is that body weight is related to health,” says Sabrena Jo, M.S., senior exercise physiologist for the American Council on Exercise.
But the fact is, a growing number experts say that just having a higher BMI might not in itself be dangerous. It’s having too much body fat that puts a person’s health at risk—whether your BMI is normal or not, says Maffetone.
Skinny fat is a better health indicator than BMI.
Right now, a person is considered overweight if their BMI is over 25, and obese if it’s over 30. But body mass index only looks at a person’s weight relative to their height. It doesn’t factor in how much lean muscle mass or body fat they have, Maffetone says.
That’s a problem, because fat tissue weighs less than muscle tissue. So a an out-of-shape guy with a high amount of body fat could end up having a lower BMI than a really fit guy who’s the same height, but has a lot more muscle tissue.
As a result, the out-of-shape, flabby guy could end up being categorized as having a normal BMI, explains Maffetone. And the fit guy could get categorized as being overweight or obese.
There’s an easy way to tell if you are skinny fat
Overfat isn’t an official diagnosable medical condition—at least not yet. But most experts agree that a person falls into the overfat category when they have enough excess body fat to put his or her health at risk. For guys, that’s 25 percent or more.
“The closer you get to 25 percent, the more you’re at risk,” Jo says.
To measure your exact amount of body fat, your doctor or a qualified trainer could perform a skin fold measurement or DEXA scan—a type of scan that measures body composition (including fat and lean muscle), Jo says.
But there’s an easier test you can give yourself right at home for a pretty good estimation: Just measure your waist size, say Maffetone and Jo.
If it’s 40 inches or larger, you have too much body fat. How your clothes fit can be another sign. “Perhaps your pants still fit, but more of you spills over the front or the sides of the waist,” Jo says. (In other words, a muffin top.)
Skinny fat can be a sign of serious health problems.
Even if your BMI is normal, having too much body fat is bad news.
That’s because excess body fat—particularly abdominal fat—produces harmful inflammatory chemicals. “Those chemicals affect the whole body, and disturb our ability to properly metabolize glucose, or blood sugar,” says Maffetone.
That can lead to insulin resistance, or the inability to properly absorb blood sugar, which can put you at risk of type 2 diabetes. And being overfat is linked to other health issues as well, like high cholesterol, heart disease, stroke, and even Alzheimer’s and cancer.
So it’s not really a surprise that guys with a normal BMI but with higher levels of abdominal fat were 78 percent more likely to die of heart disease than men with a similar BMI but less belly fat, a 2015 study in the Annals of Internal Medicine found. In fact, people of a normal weight with higher levels of belly fat had the worst expectations for long-term survival, compared with patients with normal fat distribution regardless of BMI.
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Skinny fat can be caused by unhealthy habits.
Excess body fat can happen for exactly the reasons you might expect: A diet full of empty calories and processed foods, and a sedentary lifestyle.
One of the main culprits is eating too much sugar and refined carbs. These foods prompt your body to store more body fat than foods high in complex carbs, protein, or healthy fat do, Maffetone says. It also stimulates the production of insulin, which can redeposit fat stores from other areas of the body to your abdomen, where it becomes even more dangerous.
Lack of exercise makes the problem worse. “If a person isn’t exercising regularly, they aren’t going to achieve a level of muscle mass that contributes to health,” says Jo. And if your muscle mass is low, that all-important ratio of muscle mass to fat is going to be skewed in the wrong direction.
How to reverse skinny fat
The best way to bring your body fat levels down to a healthy level is by eating right and exercising. “For most people, making good food choices may be the most effective strategy,” Maffetone says. That means cutting back on refined carbs and sugar for healthier foods like lean proteins, fruits and vegetables, low-fat dairy, and complex carbs.
You should also be active for at least half an hour most days of the week, and do some form of resistance training at least three times a week, Jo says. “That will help bring your muscle mass up. It doesn’t have to be a major two-hour workout with weights. Just enough to hit all of your major muscle groups,” she says. (Try The 21-Day Metashred from Men’s Health to fry fat fast while building muscle at the same time).
Talk to your doctor, too. Excess body fat ups your risk for high cholesterol—so it’s a good idea to have your levels tested. If they’re high, your doctor can determine whether diet and exercise alone are enough to lower them, or if you need to take meds to get your levels under control.