New Study Says This BMI Level Won’t Increase Your Risk of Early Death
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New research found that having an “overweight” BMI did not necessarily increase the risk of death.
People classified as “obese,” however, had a 21% to 108% increased risk of early death.
Experts note that excess weight is still linked to several diseases.
Body mass index (aka BMI) has been a controversial measurement for years. In fact, Prevention no longer uses BMI as an indicator of health.
A new study adds to the growing body of evidence that suggests BMI is not as helpful as people once thought for determining how healthy you are—in people with a BMI under 30, at least.
The study, which was published in PLOS One, analyzed data from 554,332 adults in the U.S. who participated in the 1999–2018 National Health Interview Study, along with data from the 2019 US National Death Index. BMI levels—which were calculated using self-reported height and weight measurements—were compared with deaths that happened over the 20-year period.
The researchers found that there wasn’t a significant increased risk of mortality in people with BMIs between 25 and 29.9 (considered “overweight” by BMI standards) when other health conditions were factored out, but there was a 21% to 108% increased risk of mortality for BMIs of 30 and up (which is considered “obese”).
There were some differences based on age, though. There was no significant increase in mortality in adults over the age of 65 with BMIs between 22.5 and 34.9, which includes the normal, overweight, and obese categories.
“BMI may not necessarily increase mortality independently of other risk factors in adults, especially older adults, with overweight BMI,” the researchers concluded. “Further studies incorporating weight history, body composition, and morbidity outcomes are needed to fully characterize BMI-mortality associations.”
The study raises even more questions about BMI and the impact of overweight on health. Here’s what you need to know.
Why might being overweight (according to BMI standards) not increase your risk of death?
Having any level of weight above what’s considered “normal” by BMI standards has long been considered a risk factor in the medical community for a slew of health issues. But this study found that it didn’t raise the risk of death. Why?
“This is not the first study to show that being slightly overweight does not greatly increase your disease risk,” says Jessica Cording, R.D., a nutritionist and the author of The Little Book of Game-Changers. “We do know that obesity is a medical condition with cardiometabolic consequences.” But things can be more muddled for people who are considered overweight, she says.
In fact, a 2013 study on nearly three million people found that those who had a BMI that classified them as overweight had a lower risk of dying than those who were classified as having a normal weight. But a study of nearly 18,000 people published last year found that having overweight or obesity increased a person’s risk of death by 22% to 91%.
“What we see in hospital and long-term care settings is that having a couple extra pounds—a BMI of 26 to 27—can help the patient to survive a really bad bout of influenza or an acute kidney disease,” says Scott Keatley, R.D., co-owner of Keatley Medical Nutrition Therapy. “Statistically, with the overweight data set these may very well balance out across a huge number of people.”
Still, Cording notes that the most recent study only focused on the risk of dying in people who have overweight—it didn’t note whether people in the overweight category had health issues like type 2 diabetes, high blood pressure, and stroke, which are linked to having excess body fat.
Keatley says that not dying while have excess body weight doesn't mean someone is healthy. “No one has ‘obesity’ or ‘overweight’ written on their death certificate,” he says. “Death related to weight usually takes the form of cancer, heart disease, stroke, and [type 2] diabetes.”
Why is BMI controversial?
Experts have argued for years that BMI doesn’t offer a complete picture of health, even though it’s often used that way. “BMI is only one piece of the puzzle,” Cording says.
Case in point: A 2016 study of more than 40,000 people found that about half of those who were classified as overweight and nearly 30% of those classified as obese were metabolically healthy. The researchers also discovered that more than 30% of people who were classified as having normal weights were metabolically unhealthy.
BMI ranges don’t factor in things like the impact of body type and ethnicity on health, Cording says—and those elements can make a difference. A study published last year of more than 2.8 million Americans, for example, found that Asian-Americans may have a higher risk of developing metabolic conditions like type 2 diabetes and high blood pressure at lower BMI thresholds than the current standards. Another study of more than 70,000 people found that Black Americans are often healthier at higher BMIs than their white counterparts.
The American Medical Association (AMA) announced last month that it has adopted new guidelines that urge healthcare providers to use more than BMI when they evaluate a patient’s health. “BMI is based primarily on data collected from previous generations of non-Hispanic white populations,” the organization said in a statement, noting that BMI is “an imperfect way to measure body fat in multiple groups given that it does not account for differences across race/ethnic groups, sexes, genders, and age-span.”
The AMA says that BMI can help determine the amount of fat mass in the general population but that it “loses predictability” when it’s applied to individuals.
How to figure out the right weight for you
There are other metrics that can help determine the best weight for your health, Cording says—they just may take a little more work.
The American Heart Association (AHA) currently recommends measuring your waist circumference, along with your weight. Belly fat, aka visceral fat, has been linked to a higher risk of health complications, including heart disease.
“I would love to see more of an emphasis on things like body composition—how much muscle vs. fat tissue someone has,” Cording says. Nutrient status is important, too, she says.
But Cording says she doesn’t expect BMI to ever fully go away. “We need to be mindful of being underweight—that carries disease risk as well—and we know that having obesity increases disease risk,” she says.
Keatley also says that BMI is likely here to stay. “BMI is a tool in the tool box and it is useful,” he says. “Being obese or underweight puts an individual at risk for other diseases—this is one of the few indicators that medical professionals can use before things get really bad. Eliminating it may eliminate the closest thing to preventative care many insurance companies cover.”
If you’re not sure what an appropriate weight is for your body, Cording recommends that you talk to your healthcare provider or a registered dietitian. They should be able to work with you to help determine this, as well as how you can be as healthy as possible.
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