A new study, published last week in theAmerican Journal of Clinical Nutrition, shows that eating dietary fructose causes liver damage in monkeys.

“Is a calorie a calorie? Are they all created equal? Based on this study, we would say not,” said Kylie Kavanagh, D.V.M., assistant professor of pathology-comparative medicine at Wake Forest Baptist and lead author of the study.

The study used monkeys in two groups over a several year period. The study was designed so that the monkeys would NOT gain weight. Both groups were fed the same number of calories, just distributed differently. One group received fructose (sugar), the other a different form of carbohydrate with equal caloric impact.

Both diets had the same amount of fat, carbohydrate and protein, but the sources were different, Kavanagh said. The high-fructose group’s diet was made from flour, butter, pork fat, eggs and fructose (the main ingredient in corn syrup), similar to what many people eat, while the control group’s diet was made from healthy complex carbohydrates and soy protein.

The results?

Not surprisingly, the animals allowed to eat as much as they wanted of the high-fructose diet gained 50 percent more weight than the control group. They developed diabetes at three times the rate of the control group and also developed hepatic steatosis, or non-alcoholic fatty liver disease.

“What surprised us the most was how quickly the liver was affected and how extensive the damage was, especially without weight gain as a factor,” Kavanagh said. “Six weeks in monkeys is roughly equivalent to three months in humans.”