Cardiorespiratory fitness trumps BMI in predicting risk of death and heart disease

As rates of obesity, as defined by body mass index (BMI), continue to climb in the United States, so have efforts to lose weight, including a new era of weight-loss drugs. Yet a new systematic review and meta-analysis published today in the British Journal of Sports Medicine found that cardiorespiratory fitness was a stronger predictor of both cardiovascular disease and all-cause mortality than BMI.

The researchers found that fit individuals across all BMI categories had statistically similar risks of death from all causes or cardiovascular disease. By contrast, unfit individuals in all BMI categories showed two- to three-fold higher risks of both all-cause and cardiovascular disease mortality compared with normal weight fit individuals. In fact, obese fit individuals had significantly lower risk of death compared to normal weight unfit individuals.

Fitness, it turns out, is far more important than fatness when it comes to mortality risk. Our study found that obese fit individuals had a risk of death that was similar to that of normal weight fit individuals and close to one-half that of normal weight unfit individuals.

Exercise is more than just a way to expend calories. It is excellent 'medicine' to optimize overall health and can largely reduce the risk of cardiovascular disease and all-cause death for people of all sizes."

Siddhartha Angadi, associate professor of exercise physiology at the University of Virginia School of Education and Human Development and corresponding author of the study

The researchers reviewed 20 studies with a total sample size of 398,716 adults from multiple countries. About one third of the participants in the studies were females, an increase of nearly three-fold from previous studies. In the majority of studies, individuals were classified as fit if their exercise stress test score (estimated or directly measured VO₂max) placed them above the 20th percentile within their age group.

Obesity is associated with a series of health conditions and weight loss has long been seen as the way to reduce the impact of those conditions. But weight loss is challenging and failing to keep weight off can bring other risks.

"Most people who lose weight regain it," said Glenn Gaesser, professor at Arizona State University and co-author of the study. "Repetitive cycles of losing and gaining weight-;yo-yo dieting-;is associated with numerous health risks comparable to those of obesity itself. Improving cardiorespiratory fitness may help avoid the adverse health effects associated with chronic yo-yo dieting."

Approximately 20% of US adults meet the physical activity guidelines set by the U.S. Department of Health and Human Services. Current guidelines recommend adults perform a minimum of 150 minutes per week of moderate-intensity physical activity or 75-minutes of vigorous physical activity along with muscle strengthening for two days a week. For those who find themselves in the bottom 20th percentile of cardiorespiratory fitness, beginning any kind of aerobic exercise could have a big impact.

"The largest reduction in all-cause and cardiovascular disease mortality risk occurs when completely sedentary individuals increase their physical activity modestly," Angadi said. "This could be achieved with activities such as brisk walking several times per week with the goal of accumulating approximately 30 minutes per day."

The researchers note that the study examines data from large epidemiological studies and recommend that it is time to independently assess the value of a fitness-based approach rather than a weight-loss approach in obese individuals to optimize health outcomes.