UF study suggests body fat is better predictor of diabetes risk than BMI

Current guidelines call for adults with high body mass index, or BMI, to be screened for prediabetes and diabetes. But under these recommendations, physicians might be missing another high-risk group: people who have a BMI in the normal range, but a high percentage of body fat.

A new University of Florida study finds that people who have a normal BMI, but a high body fat percentage, were more likely to have prediabetes or diabetes than people who have lower body fat, but a BMI that categorizes them as overweight. The findings appear in the journal BMJ Open.

Body fat percentage refers to the proportion of fat to lean muscle, while BMI is calculated by dividing a person’s weight by his or her height.

“Typically, normal BMI has been perceived as healthy, so people with normal BMI have been neglected in several preventive care guidelines. Yet, normal BMI does not necessarily mean healthy body composition,” said lead investigator Ara Jo, Ph.D., a clinical assistant professor in the department of health services research, management and policy at the UF College of Public Health and Health Professions, part of UF Health.

The findings support previous research suggesting that people with healthy weight obesity, also known as “skinny fat,” may be at significant risk for some health problems that have traditionally been associated with high body weight, including diabetes and cardiovascular disease. A 2016 UF study found that one-third of healthy weight adults over the age of 45 met the criteria for prediabetes.

“Evidence has been mounting that BMI may not be the best measure of body fat for a variety of groups like individuals who are sedentary or older women,” said the study’s senior author Arch G. Mainous III, Ph.D., chair of the UF department of health services research, management and policy. “This study provides more support for this idea of skinny fat and shows how percent body fat is more important in identifying individuals with prediabetes than BMI. It also alerts us to consider ways of better identifying individuals with elevated body fat and incorporating it into clinical practice.”

For the study, the UF researchers analyzed data for the years 1999 to 2006 from the National Health and Nutrition Examination Survey, a nationally representative study that uses a combination of interviews, physical examinations and laboratory tests. They focused on adults age 40 and older who had never received a diabetes diagnosis. While there are no universally accepted cutoffs for high body fat, the researchers used guidelines from the American Association of Clinical Endocrinologists and the American College of Endocrinology, which classifies 25 percent and above as high body fat for men, and 35 percent and above as high body fat for women. Participants’ body fat was measured using a whole-body dual-energy X-ray absorptiometry, or DXA, scan.

They found that 13.5 percent of peoplea who had normal BMI and high body fat met the criteria for prediabetes or diabetes compared with 10.5 percent of people with an overweight BMI, but lower body fat.

“This high body fat percent link to abnormal blood glucose holds up even when we control for things like age, sex, race/ethnicity, family history of diabetes, vigorous-intensity exercise and muscle strengthening activities,” Mainous said.

The researchers encourage clinicians to integrate body fat measures with BMI to identify people who may need screening for prediabetes and diabetes.

“We hope these findings may inspire physicians and other health professionals to look more closely at the normal BMI population and provide preventive care on time for those who are at risk of developing diabetes,” Jo said.