Some people who do not see the scale move in a positive direction soon after they start an exercise routine will just quit. But researchers at the University of Virginia say that's not a good idea because being fit is more important than not being fat when it comes to mortality risk.

UVA scientists looked at a total of 20 studies with almost 400,000 participants from multiple countries and concluded fit individuals shared similar risks of death and cardiovascular disease regardless of their weight. Fit people who were technically obese according to their body mass index (BMI) had a significantly lower risk of death compared to people of normal weight who were not fit.

"Fitness, it turns out, is far more important than fatness when it comes to mortality risk," said Siddhartha Angadi, associate professor of exercise physiology at the University of Virginia School of Education and Human Development. "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."

Most of the studies used the 20th percentile as the benchmark for fitness. Those who scored above the 20th percentile among their peers in an exercise stress test were considered fit.

"I believe this study will help strengthen the growing body of literature in the 'fitness vs. fatness' debate," said study co-author Nathan Weeldryer. "As a society, we tend to equate body weight or fatness with health status. Our study, which features the largest and most globally representative sample to date, along with more rigorous statistical analysis compared to previous research, aims to shift perspectives on the relationship between fitness and body fat."

Obesity contributes to a wide range of health problems. Weight loss has long been championed as a way to reduce the impact, but it's a challenge many have a hard time meeting.

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

Click here to read more in the British Journal of Sports Medicine.