Add one more to the long list of reasons to keep active: A new University of Florida study demonstrates that low levels of physical activity are associated with higher blood sugar among adults who are at a healthy weight.

The findings, which appear online ahead of print in the American Journal of Preventive Medicine, may help explain why up to one–third of adults who are slender have prediabetes, a condition that puts them at risk for developing diabetes and other health problems.

“We have found that a lot of people who we would consider to be at healthy weight — they’re not overweight or obese — are not metabolically healthy,” said lead investigator Arch G. Mainous III, PhD, chair of the department of health services research, management and policy in the UF College of Public Health and Health Professions, part of UF Health.

These individuals may have healthy weight obesity, also known as normal weight obesity or “skinny fat.” The condition is characterized as having a body mass index within the normal range, but a high proportion of fat to lean muscle, typically more than 25 percent body fat in males and 35 percent in females. People with healthy weight obesity are more likely to develop metabolic syndrome, which includes increased blood pressure, high blood sugar and abnormal cholesterol levels.

Because screening guidelines for prediabetes and diabetes typically focus on adults who are overweight or obese, individuals at a healthy weight who have high blood sugar levels may go undetected.

For the UF study, researchers set out to test the hypothesis that a sedentary lifestyle may contribute to metabolic changes that put people who have a healthy weight at risk for prediabetes or diabetes. The team analyzed data from the 2014 Health Survey for England, an annual survey that combines information from personal interviews with lab tests and physical measurements collected by a nurse. The researchers assessed more than 1,000 individuals age 20 and older who had a BMI within the healthy weight range of 18.5 to 24.9 and who did not have a diagnosis of diabetes.

Researchers found that participants who reported having a sedentary lifestyle were more likely than their more active counterparts to have a blood glucose level at or above 5.7, which the American Diabetes Association considers prediabetes. Among participants with low activity levels, about one–quarter of all participants and more than 40 percent of adults 45 and older met the criteria for prediabetes or diabetes.

“Our findings suggest that sedentary lifestyle is overlooked when we think in terms of healthy weight,” said Mainous, the Florida Blue endowed chair of health administration. “We shouldn’t focus only on calorie intake, weight or BMI at the expense of activity.”

Mainous said more research is needed to better understand the health implications of healthy weight obesity as well as how much and what type of activity, whether it is weight–bearing or resistance training, for example, may be most effective at combating metabolic syndrome.

The UF study adds to a growing body of research that illustrates the potential negative health effects of low levels of physical activity, Mainous said.

“Don’t focus solely on the scale and think you’re OK,” he said. “If you have a sedentary lifestyle, make sure you get up and move.”