July 06, 2023
A body mass index in the range of overweight or obese does not necessarily increase the risk of death on its own, according to a new study.
The study, published Wednesday in the journal PLOS One, found that having a BMI that is considered overweight or obese did not significantly increase the risk of death for people over 65. The same was true for younger adults with BMIs that deemed them slightly overweight. But for younger adults with BMIs greater than 27.5, the risk of death increased by 21% to 108%.
The study examined data from 554,000 adults from 1999 to 2018. Researchers also concluded that BMI may not necessarily increase the risk of death independently of other risk factors like substance use, eating disorders, lifestyle habits and genetics. But they stressed that more studies are needed to assess weight history, body composition and risk of illness.
The findings build on a growing body of research that suggests BMI alone is not an accurate indicator of one's health. Health experts have more begun to criticize the use of BMI, which measures body fat based on height and weight, to assess one's health without considering other factors, including a person's age, race and environment.
"Our results are basically confirming a lot of other studies that have been done in recent years — not at this large of a level, but basically confirming that BMI by itself is really a poor indicator of health risk," Dr. Aayush Visaria, an internal medicine resident at Rutgers Robert Wood Johnson Medical School and co-author of the study, told NBC News. "This kind of adds to the idea that clinicians should be using different measures of body fat to diagnose obesity, not just BMI. I think in the future these measures will become commonplace."
BMI has been used for decades to determine whether a person is considered overweight or obese. A healthy BMI is between 18.5 and 24.9, and an overweight BMI is between 25 and 29.9. A BMI of 30 or higher is considered obese.
Though BMI is a common obesity screening method, it measures excess weight but not excess fat, according to the U.S. Centers for Disease Control and Prevention. It does not take into account differences in muscle mass, bone mass or excess fat, and does not provide any information about the distribution of fat in the body.
The CDC notes that older adults tend to have more body fat than younger adults, but with lower BMIs. Women tend to have more body fat than men with equivalent BMIs, and highly-trained athletes may have higher BMIs than more sedentary people due to increased muscle mass.
Previous research has suggested that obesity assessments that rely on BMI may leave out people who are actually obese and include people with healthy weight levels. In a 2016 study, nearly half of the participants considered overweight and 29% of those considered obese were metabolically healthy. And some people considered healthy were metabolically unhealthy.
Last month, the American Medical Association adopted a new policy that advised health care providers to consider measures of visceral fat, body mass, body composition, waist circumference, relative fat mass and genetics alongside BMI.
The policy said BMI has a "problematic history," noting it has been used for racist exclusion and that it is based primarily on data from non-Hispanic white people. The AMA said understanding how a person's age or race factors into weight change is important in determining a person's health risk and whether to recommend weight loss.
"(BMI) does not distinguish between muscle mass and fat mass, and some individuals like bodybuilders may have a high BMI because of more muscle mass," Dr. Dagfinn Aune, research associate in the School of Public Health at Imperial College London, told MedicalNewsToday. "In spite of these limitations, BMI does a pretty decent job in capturing the increased chronic disease and mortality risk at the population level associated with adiposity (having too much fatty tissue in the body)."
Using BMI to help guide patients toward healthier lifestyle choices can reduce the risk of diseases like type 2 diabetes, heart disease, high blood pressure, high cholesterol, breathing problems, joint problems, gallbladder disease, stroke, mental illnesses and some types of cancer, according to the CDC.
Obesity rates have been steadily rising in the United States for years. Nearly half of all U.S. adults are expected to be obese by 2030. By that time, the obesity rate is expected to be as high as 50% in 29 states, including Pennsylvania.
