“Our study should be the final nail in the coffin for BMI."
Body mass index (BMI) has been used by doctors and physicians for years now — it’s a measurement of body fat based on an individual's weight in relation to height. However, since BMI only relies on a simple calculation of body fat, a new study highlights that it might not be an accurate predictor of weight-related health issues like diabetes or heart disease.
In fact, based on the results of the new study, the researchers suggest that about 75 million adults in the United States may be misclassified as either having a lower or higher risk of heart disease or diabetes than suggested by their BMIs.
The scientists looked at the BMIs of about 40,000 adults in the US. They also looked into these individuals’ “cardiometabolic health,” which includes data on blood pressure, blood sugar, cholesterol, inflammation, and insulin levels — big indicators for risk of heart disease and diabetes.
The researchers defined a “healthy” person as one who had healthy values for four or more of these indicators.
After looking at the relationship between BMI and cardiometabolic health, the researchers found that almost half of the people with a BMI in the “overweight” range, 29 percent of people with a BMI in the “obese” range, and 16 percent of the people in the “very obese” range were actually cardiometabolically healthy.
"In the overweight BMI category, 47 percent are perfectly healthy," researcher Jeffrey Hunger from the University of California, Santa Barbara, said in a press release. "So to be using BMI as a health proxy – particularly for everyone within that category – is simply incorrect. Our study should be the final nail in the coffin for BMI."
The researchers hope that these results, published in the International Journal of Obesity, will help dispel the common assumption that people who are obese are automatically unhealthy in all other health-related aspects.
"Many people see obesity as a death sentence," lead study author A. Janet Tomiyama, an assistant professor of psychology at the University of California, Los Angeles, said in a statement. "But the data show there are tens of millions of people who are overweight and obese and are perfectly healthy."
Additionally, more than 30 percent of the people with BMIs in the normal weight range were found to be cardiometabolically unhealthy.
"Not only does BMI mislabel 54 million heavier individuals as unhealthy, it actually overlooks a large group of individuals considered to have a 'healthy' BMI who are actually unhealthy when you look at underlying clinical indicators," said Hunger in the press release. "We used a fairly strict definition of health. You had to be at clinically healthy levels on four out of the five health indicators assessed."
A prime example of how BMI can paint an inaccurate picture of health is when it’s used to calculate the health of athletes — picture a big, bulky football player. Chances are his BMI will be classify him as heavy enough to be overweight or obese, but in reality, this is because his muscle mass weighs more than the average Joe.
These scientists aren’t the first to highlight the limitations and flaws of using BMI to measure health, but it’s still widely used by US companies to determine employee health insurance costs. Despite the fact that BMI is easy and quick to calculate, it’s worth the while to put in a little more time and effort to produce more accurate results about an individual’s health status.
"We need to move away from trying to find a single metric on which to penalise or incentivise people and instead focus on finding effective ways to improve behaviours known to have positive outcomes over time," said Hunger.