The new study included information from U.S. National Health and Nutrition Examination Surveys, representing nearly 24,000 men and women, aged 20 to 74.
"Changes over time in the distribution of age, race and ethnicity, and obesity in the population explained all of the increase in women but only half of the increase in men," Menke said.
He can't explain from this study why men's diabetes rates are increasing more than women's are, or exactly what factors are behind that rise.
Nor is it known, he said, why weight plays a role in some people developing diabetes but not others. "It's not entirely clear why some people who have maintained a healthy weight their entire lives develop type 2 diabetes while other people who are obese never develop it," he said.
Menke and other experts believe genetics may play a stronger role for some people than others.
Both genetics and environmental factors drive diabetes risk, said Dr. Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center, in New York City. "There has been [ongoing] debate about how much is genetic and how much environmental."
Still, obesity is likely the biggest factor behind the increase in type 2 diabetes, noted Zonszein. It's also important because it's a modifiable risk factor, which means it's a risk factor people can change, according to the study's authors.
Zonszein pointed out at least one limitation of the study -- their use of body mass index (BMI) as a measure of obesity.
The authors, too, noted that using BMI to measure how much fat a person has (also called adiposity) is a limitation of the study, and that other measures, such as a person's waist circumference, may be more strongly linked with diabetes. However, the surveys used only measured BMI, not waist circumference.
To better predict diabetes risk, according to Zonszein, it's better to measure adiposity in other ways,
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