July 6, 2023 — Eric Collard has always been an athlete; he played college football, got into triathlons in adulthood, and now at age 44, regularly rides his bike, runs, lifts weights, plays golf, and more. The Ottawa-based director of a nonprofit, Collard also takes his nutrition seriously. By almost all measures — blood pressure, cholesterol, blood sugar — Collard is fit and healthy.
The one outlier among Collard’s health markers is his body mass index (BMI), which puts him in the obese category. “I’m a big guy,” he says of his 6’4’’ height and his 258-pound weight. “But I’m also healthy, and BMI should not be the end measurement of health.”
Body mass index has been around since the early 19th century, but it was the mid-1980s when doctors began using it to define obesity in the United States. It has stuck around for decades, even though many members of the medical community consider it flawed — a patient like Collard demonstrates why.
A new study from Rutgers University is shedding some light on the accuracy of BMI as a sign of increased mortality risk. The results? When classified as obese by BMI alone, the measurement largely gets it wrong.
“The literature on BMI has been inconsistent, and so we wanted to address the limitations of prior studies,” said study co-author Aayush Visaria, MD, an internal medicine resident doctor at Rutgers New Jersey Medical School. “The population makeup in the United States has shifted, so it was also time to redo the research on today’s population.”
To conduct the research, Visaria and his team analyzed data from more than 500,000 U.S. adults from the 1999-2018 National Health Interview Survey and the 2019 U.S. National Death Index. BMI in these cases was calculated from self-reported height and weight. They included data on demographics, socio-behavioral factors, comorbidities, and health care access. They divided the group into nine BMI categories.
The makeup was on average 46 years old, 50% female, and 69% non-Hispanic white. Of those people, 35% had a BMI between 25 and 30, which is defined as overweight, and 27.2% had a BMI above or equal to 30, which classifies them as obese. Visaria and his team then followed up at a median of 9 years, with a maximum of 20 years, which showed 75,807 participants had died. When breaking the data down into racial categories, the team did find increased risk of mortality among Hispanic participants who were overweight, but not among Black or White participants. In general, once a BMI hit 30 and above, however, mortality did go up.
The Rutgers group concluded that additional studies are needed to better incorporate weight history, body composition, and causes of death. They also determined that BMI alone should not drive clinical decisions.
Moving Away From BMI
Visaria says that while BMI alone is a flawed measure of health, he understands why it has been a popular method in the medical community. “It’s a simple calculation,” he said, “and it’s trackable and scalable. Public health still uses it for those reasons.”
Matthew Davis, MD, a bariatric surgeon at Methodist Medical Group in Memphis, agreed with this analysis. “Unfortunately, the same factors that make it easy to use – it simply looks at a person’s height and weight, which are easily measurable, also make it subject to criticism,” he said. “Its simplicity means it does not take into account the myriad other factors that can contribute to increased weight or poor health, namely social, environmental or genetic factors.”
Lately, there’s been a shift away from the long-standing health metric. In June at the annual meeting of the American Medical Association, delegates adopted a new policy aimed at clarifying how BMI should be used in medicine.
In a press release, the association had this to say: “The AMA recognizes issues with using BMI as a measurement due to its historical harm, its use for racist exclusion, and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations.”
Because of those limitations, the association said, it “suggests that it be used along with other “valid measures” of risk, including what’s known as visceral fat, which is fat hidden deep in the body, estimated body fat, waist circumference and genetic/metabolic factors,” among other things.
Wendy Schofer, MD, founder of Family in Focus, is among the doctors who have long believed BMI is flawed. “Obesity as defined by BMI doesn’t say anything about the health of an individual at a certain BMI,” she said. “We make a ton of assumptions based on those numbers.”
Instead, Schofer suggested, doctors need to better understand their patients and their lifestyles. “We need to understand what is important to the induvial, what health means to them, and how to develop and reach goals that are important to them,” she said. “I remove weight and BMI from the conversation. Instead, we talk about how we want to feel, what we want to do, and how we want to be.”
Collard said his doctor takes a more holistic approach to his visits, as well, something he appreciates. “My doctor acknowledges that my BMI is irrelevant to my overall health,” he said.
Visaria said his latest study is step one in a necessary, ongoing series on BMI. He recently shared results from a study on bone density scans and BMI, which showed the limitations of both in visualizing the relationship between lean mass and bone density. Future studies will incorporate measurements of fatty tissue, cardiovascular disease, high blood pressure, and other metrics. “We want to look into the long-term implications on morbidity,” he said. “Providers need to take into account a wide variety of other measures beyond BMI.”