A new study shed light on why a diet high in fructose contributes to the development of obesity and diabetes.

Previous studies have linked fructose consumption to obesity, diabetes, liver disease and metabolic syndrome. Metabolic syndrome, a group of risk factors that raises the risk for diabetes, heart disease, stroke, and other health problems, currently affects more than one in four Americans, and the research indicates fructose intake causes features of metabolic syndrome in animals and humans.

Put simply, this means a diet with more fructose will lead to a greater accumulation of dangerous fat around organs and higher insulin resistance than one that’s higher in starch — even if they both have the same number of calories.

An international team of researchers, led by senior author Dr. Richard Johnson, Chief of the Division of Renal Diseases and Hypertension at the University of Colorado School of Medicine, found that in mice, fructose is metabolized by two forms of an enzyme — fructokinase C and fructokinase A — and they have very different effects. One causes fatty liver, obesity, and insulin resistance, while the other actually protects against them.

“By reducing the amount of fructose for metabolism in the liver, fructokinase A protects against fructokinase C-mediated metabolic syndrome,” the authors wrote in a study published Monday in the Proceedings of the National Academy of Sciences, adding that their work provides “insights into the mechanisms by which fructose causes obesity and metabolic syndrome.”