A body mass index in the range considered overweight, or even obese, is not necessarily associated with an increased risk of death, a new study has found. The research is the latest addition to a growing body of evidence suggesting that BMI alone is not an accurate indicator of a person’s health.
The study, published Wednesday in PLOS One magazineevaluated the relationship between BMI and the risk of death from any cause, based on data from more than 550,000 US adults for an average of nine years.
The results did not show a significant increase in the risk of death for those older than 65 years with a BMI between 22.5 and 34.9. The same was true for younger adults with BMIs between 22.5 and 27.4. A BMI of 25 or higher is considered overweight and 30 or higher is considered obese.
The BMI is calculated by dividing a person’s weight by the square of their height. For decades, it has been used to assess whether a person’s weight is “healthy” or whether they might pose a risk of diabetes or heart disease. But many health professionals have criticized this, saying that the BMI does not take into account crucial factors such as percentage of body fat and variations in disease risk among people of different races and genders.
Last month, the American Medical Association adopted A politic advise physicians to use additional measures, including waist circumference, body fat distribution, and genetic factors, to assess a patient’s health.
The study findings support the new guidelines, according to Dr. Aayush Visaria, an internal medicine resident at Rutgers Robert Wood Johnson Medical School and co-author of the new study.
“Our results basically confirm a lot of other studies that have been done in recent years, not to such a big level, but basically confirm that BMI itself is really a poor indicator of health risk,” Visaria said.
Waist circumference, he added, might be a stronger indicator: The study compared people with the same BMI but different waist circumferences and found that the latter was associated with an increased risk of death overall.
However, the study results showed that participants with a BMI of 30 or higher faced a higher risk of mortality. Among younger adults, a BMI of 27.5 to 29.9 was also associated with nearly 20% increased risk.
Dr. Fatima Stanford, an obesity medicine specialist at Massachusetts General Hospital who was not involved in the new research, said BMI may equate thinness with health at the expense of other important factors. Substance abuse disorders, tobacco use and eating disorders can lead to a leaner physique, she noted, but they don’t mean a person is healthy.
“The reason I keep hearing why we should use it is because it’s easy,” Stanford said. “Just because it’s easy doesn’t mean it’s right.”
Previous research has revealed problems with the use of BMI to assess whether a person is obese or at risk for weight-related diseases. in a 2016 studyalmost half of the participants considered overweight and 29% of those considered obese were found to be metabolically healthy, while more than 30% of those with weights considered “normal” were not metabolically healthy.
Similarly, other research that Visaria presented last month indicated that people with “normal” BMIs can still be obese.
Stanford also emphasized that the BMI ranges considered overweight or obese do not take into account the differences that arise between racial and ethnic groups. Some research suggestsfor example, that Asians may face a higher risk of developing metabolic diseases such as diabetes and hypertension with a BMI below general thresholds.
Meanwhile, black women are often healthy with BMIs in the overweight and obese ranges, Stanford said. TO 2013 study found a higher BMI was not as strongly associated with mortality risk in African-Americans as it was in whites.
In the new study, the authors noted that some earlier studies that had found a link between BMI and higher mortality used US data from the 1960s to the 1990s, with mostly white participants. But non-Hispanic whites made up 58% of the US population in 2020, up from 85% in 1990, so those earlier data sets may be less applicable, Visaria said.
Participants in the new study were 69% white, 12% black, 14% Hispanic and nearly 5% Asian, which Stanford says is comparatively “large representation.”
However, Dr. Jaime Almandoz, medical director of the Weight Wellness Program at UT Southwestern Medical Center in Dallas, pointed out some shortcomings in the study. For one thing, he said, it focuses solely on the relationship between BMI and risk of death.
“There is much more to life than not dying,” said Almandoz, who was not involved in the new research. “Studies like this can be misinterpreted as saying, ‘Well, up to a BMI of 30 is OK, or ‘Up to a BMI of 35 in older adults is OK,’ but that doesn’t mean a person isn’t living with Type 2 Diabetes or is at increased risk.” of heart attack, stroke, heart failure.”
According the Centers for Disease Control and PreventionPeople with a BMI of 25 or more face an increased risk of high blood pressure and cholesterol, type 2 diabetes, and several types of cancer.
Almandoz also pointed out that the study underrepresents the proportion of obese people. About 27% of the participants had a BMI greater than 30, while a CDC survey estimated that 42% of American adults are obese.
Visaria said that if the study had looked at the fat percentages of the participants, it could have found that more than 27% were obese. But that’s precisely the problem, she added: BMI doesn’t measure the proportion of body fat.
“This adds to the idea that clinicians should use different measures of body fat to diagnose obesity, not just BMI,” he said. “I think in the future these measures will become common.”
