Diabetes: Body fat percentage, not BMI, predicts risk

The results of a new study urge healthcare providers to account for body fat distribution, in addition to body mass index, in their decision to screen people for diabetes and prediabetes.

Body mass index (BMI) is a traditional measurement that divides a person's weight by their height to find out whether they have a healthy weight.

However, increasing amounts of studies have been questioning its usefulness and accuracy as an indicator of cardiometabolic health.

The distribution of fat, rather than the total amount, these studies suggest, may give us more clues about the risk of conditions such as insulin resistance, high blood pressure, heart disease, and even cancer.

For instance, a recent study drew attention to the "overfat pandemic" that is spreading across the United States. The researchers used the term overfat to describe the accumulation of fat around certain parts of the body, which, the scientists point out, is not accounted for by BMI.

In fact, a low BMI may be misleading. Belly fat is particularly harmful, research shows, with some studies showing that it can raise the risk of diabetes and heart disease while others reveal the mechanisms behind this association.

Now, a new study — which has been published in the journal BMJ Open — adds to this growing body of research, as researchers from the University of Florida (UF) in Gainesville discover that people with a normal BMI but high body fat are more prone to prediabetes or diabetes, when compared with people deemed overweight according to their BMI but have a lower body fat percentage.

Body fat percentage calculates the proportion of a person's fat mass to their lean muscle mass.

High body fat, not BMI, predicts diabetes

For this study, the scientists — led by Ara Jo, Ph.D., a clinical assistant professor in the Department of Health Services Research, Management and Policy at UF — examined data available from the National Health and Nutrition Examination Survey.

This survey was carried out by the National Center for Health Statistics of the Centers for Disease Control and Prevention (CDC), and it used interviews, as well as physical and laboratory tests, to examine the health of adults aged 40 and above between 1999 and 2006.

Jo and her team focused on adults who had never been diagnosed with type 2 diabetes, and they used a scanning technique called dual-energy X-ray absorptiometry — which is the most accurate technique available — to measure body fat percentage.

They used the guidelines issued by the American Association of Clinical Endocrinologists and the American College of Endocrinology to estimate what counts as high body fat for men and for women.

According to these guidelines, having a percentage of body fat of 25 and above is considered high for men, and 35 percent is considered high body fat for women.

Based on these measurements, the analysis revealed that 13.5 percent of people with a normal BMI and a high body fat percentage had prediabetes or diabetes, compared with only 10.5 percent of those deemed "overweight" by their BMI but who had low body fat.

"This high body fat percent link to abnormal blood glucose," explains senior study author Arch G. Mainous III, the chair of the UF Department of Health Services Research, Management and Policy, "holds up even when we control for things like age, sex, race/ethnicity, family history of diabetes, vigorous-intensity exercise, and muscle strengthening activities."

Normal BMI not a measure of health

"Typically, normal BMI has been perceived as healthy," explains Jo, "so people with normal BMI have been neglected in several preventive care guidelines."

"Yet, normal BMI does not necessarily mean healthy body composition," she cautions. Mainous echoes the same thoughts, saying, "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."

"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."

Arch G. Mainous III

"It also alerts us," he adds, "to consider ways of better identifying individuals with elevated body fat and incorporating it into clinical practice."

"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," concludes Jo.