BMI or VO2? What Is A Good Measure?

Body mass index (BMI) has been a controversial health measurement for years, with critics pointing out that it can be misleading. For instance, it doesn't distinguish between the muscle mass and fat mass. Still, it's a relatively easy stat for doctors to calculate, so it continues to be used in the medical field.

Now, a new analysis of scientific data finds that a different metric is far superior at calculating cardiovascular and other health risks.

The study, which was recently published in the British Journal of Sports Medicine, analyzed data from 20 studies of nearly 400,000 people where a person’s cardiovascular fitness was compared to their BMI. (The researchers measured fitness with a VO2 peak exercise test—more on that in a second.) The scientists also looked at the study participants’ risk of cardiovascular disease and all-cause mortality.

Researchers discovered that people who had overweight or obesity but were fit didn’t have a statistically significant higher risk of dying or developing heart disease. But people who were not fit had a two- to three-times greater risk of dying, regardless of their weight.

"From a health perspective, the risks of being unfit are far worse than the risks associated with carrying extra weight," lead author Siddhartha Angadi, PhD, an associate professor in the department of kinesiology at the University of Virginia, told Runner's World. "This study builds on a large body of research over the past three decades that underscores the importance of fitness over fatness."

In an ideal world, doctors would gauge health risks by measuring exercise capacity, Angadi added, noting that it should be considered a "vital sign" like blood pressure, pulse rate, and temperature.

VO2 max is a measure of how much oxygen your body absorbs and uses while you work out. (V stands for "volume" while "O2" is for oxygen.)

BMI stands for body mass index. It’s a calculation of your height relatively to your weight, according to the Centers for Disease Control and Prevention (CDC). BMI is generally classified into underweight, healthy weight, overweight, and obesity—although obesity is subdivided into three classes.