High BMI? What It Says (or Doesn't Say) About Your Health
There's been a lot of talk about BMI lately. Here's what the different ranges mean
En español | As the COVID vaccine rollout continues, some people are finding an unexpected upside to their pandemic weight gain — a faster route to vaccination. While obesity can raise your risk for COVID-19 and its worst outcomes, now it may put you ahead of others in the vaccination race.
That was the case for Andrew Lavin, 61, owner of a strategic communications firm in Port Washington, N.Y. He called his doctor as soon as he learned that his body mass index (BMI) — a measure used to estimate body fat and disease risk — might shorten his wait for a vaccine. “I tipped the scales at 203, and that was apparently enough to put me in the 30-plus BMI category,” he says.
While COVID has focused new attention on BMI, the measure was invented back in the early 1800s by a Belgian statistician as a way to study populations of people. The concept really took off in the early 1970s, when it was widely adopted by researchers and insurance companies.
BMI is expressed as a ratio of weight to height, and slots people into four categories based on their score: underweight (BMI below 18.5), normal or healthy weight (BMI of 18.5-24.9), overweight (BMI of 25.0-29.9), and obese (BMI of 30 and above). (Calculate yours here.)
Research shows that the higher your BMI, the higher your risk to be hospitalized with COVID-19 as well as heart disease, high blood pressure, breathing problems, type 2 diabetes, gallbladder disease and cancer.
But while BMI has served as a go-to yardstick for some time, “it's not a perfect measure,” says David Creel, a psychologist and registered dietitian at the Bariatric & Metabolic Institute at Cleveland Clinic.
What BMI doesn't tell you
That could be an understatement. BMI is certainly better than just watching the numbers on the scale. But it doesn't differentiate between the weight from fat and that from muscle, which can make a significant difference in a person's health.
"The BMI doesn't account for body composition,” says Creel. “So you might have someone with a BMI of 28, who is an athlete and in great shape with a low waist circumference, and someone with the same BMI of 28 with thin arms and legs, a lot of weight around their midsection, and problems like diabetes and hypertension. BMI-wise, they look exactly the same, but from a health perspective, they're not. BMI does not capture that at all."
This limitation may be exacerbated by age, since people tend to lose muscle mass as they get older. “As we age, we tend to lose muscle and, on average, will have more body fat for a given BMI,” Creel says.
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Body shape and other physical differences can also change the equation. “Someone with a larger frame may carry extra weight without as many risks as someone with the same BMI that has a smaller frame,” says Creel.
Although rising BMI correlates with poorer health on average, Creel does see people with high BMIs and no notable health condition. “We call them people who are ‘metabolically healthy,'” he says. “Just because someone has a higher weight doesn't necessarily mean they have high risks related to their weight.”
In fact a 2016 study in the International Journal of Obesity found that about 50 percent of Americans that fall into the overweight BMI category, and 30 percent of those classified as obese, were metabolically healthy, based on factors like blood pressure, blood sugar, cholesterol and levels of triglycerides — a particularly harmful type of blood fat.
Overreliance on BMI also misses other important clues to a person's health. Experts say it's important to know how fat is distributed throughout your body, not just the percentage of fat.
How waist size factors in
Take waist circumference — “a proxy for how much weight you have in the midsection,” Creel says. “What we're concerned about is what's called visceral fat — the fat around the organs. It's the most harmful place for people to carry it, versus carrying it in their legs or their rear.” (To measure your waist circumference, place a tape measure along your waist, using your belly button as a guide. If your waist measurement is greater than 35 inches for women, and 40 inches for men, you may be courting serious health woes.)
In addition, labeling people as overweight and obese, as BMI does, can have other detrimental effects. “Weight discrimination and bias limit opportunities in the workplace and elsewhere,” says Iliya Gutin, a doctoral candidate in sociology at the University of North Carolina-Chapel Hill Carolina Population Center.
That said, BMI still plays an important role in gauging health risks. Experts say it's best used as a starting point to a discussion on how to address your specific vulnerabilities, taking into account other factors like your blood sugar and cholesterol. “We'll ask patients about their lives,” Creel says. “What does their physical activity look like? What are their labs and blood pressure?"
Watching your own BMI
And even if you stay in the normal weight category, rising weight could signal problems. “A BMI that is creeping up as we age should, at a minimum, cause us to look for the reason this is occurring and what other changes are accompanying this increase in weight,” Creel says. “If someone's diet is poor, they are physically inactive, they are having increased knee, back, or hip pain, or their cholesterol or blood glucose is also going up, it is concerning."
Lavin is keenly aware of his own health risks. Fortunately, while protecting him from disease, his COVID vaccination is also reminding him to take better care of himself. “Now I'm working on getting rid of my ‘COVID 19 pounds’ — all the weight I put on during the pandemic not going to the gym and working out."