Body mass index, everyone's least favorite health indicator, took another hit this week in a study published in the Annals of Internal Medicine.
The study, which followed more than 50,000 middle-aged and older Canadians, found that body fat percentage is a better predictor of life expectancy than BMI. Being on the thin side or having a low BMI didn't protect against early death. In fact, mortality rates increased as BMI decreased and body fat percentage went up.
"The key is that BMI does not measure fat," lead author Dr. Raj Padwal, a professor of medicine and dentistry at the University of Alberta, told The Huffington Post. "It measures body mass, and [that] includes lean tissue."
Both low levels of lean mass and high levels of body fat are independently associated with increased risk of death, Padwal explained, so a direct measure of body fat is really the most accurate way to determine health.
"We really should not be using BMI to measure obesity," he said. "We should be using a direct measure of obesity like body fat. When a direct measure is used, then body fat is associated with increased death risk."
Aside from misleading individuals looking to measure their health, Padwal said that BMI can be frustrating from a public health and research standpoint because many health recommendations are formulated from research that relies on BMI to measure obesity.
"There are a lot of studies based on BMI telling people that being fat is healthy," he said. Instead, he suggests, many of the high-BMI participants of these studies may have low body fat and high lean mass.
While diagnostics to calculate body fat exist, such as bioelectrical impedance analysis or DEXA scanning, they can be costly. "We need better and cheaper ways to do this," Padwal said.
There is one cheap predictor of health, and that's where you carry fat on your body. People who carry weight around their midsections ("apple-shaped" people) are at higher risk for death and disease than those who carry weight around their hips ("pear-shaped" people).
If you want a rough proxy of your body fat without investing in a pricey diagnostic test, experts recommending calculating your waist-to-hip ratio. For men, the ratio should be no higher than 0.90, for women, no higher than 0.83.
For people with high levels of body fat, working out is especially important. Even moderate exercise targets the unhealthy visceral fat that collects around your internal organs, and can translate to huge health benefits. In fact, a study published in the journal Obesity in 2010 found that sedentary women who started moderate twice-weekly fitness programs lost 10 percent of their visceral fat during their year in the study.