Total caloric intake was lower in the mice that consumed the fructose-sweetened water than in the other groups, except for the control animals provided with water only.
"We were surprised to see that mice actually ate less when exposed to fructose-sweetened beverages, and therefore didn't consume more overall calories," said Dr. Tschöp. "Nevertheless, they gained significantly more body fat within a few weeks."
Results from an earlier study in humans led by Peter Havel, DVM, PhD, an endocrinology researcher at the University of California, Davis, and coauthored by Dr. Tschöp, found that several hormones involved in the regulation of body weight, including leptin, insulin and ghrelin, do not respond to fructose as they do to other types of carbohydrates, such as glucose.
Based on that study and their new data, the researchers now also believe that another factor contributing to the increased fat storage is that the liver metabolizes fructose differently than it does other carbohydrates.
"Similar to dietary fat, fructose doesn't appear to fully trigger the hormonal systems involved in the long-term control of food intake and energy metabolism," said coauthor Dr. Havel.
The researchers say that further studies in humans are needed to determine if high-fructose corn syrup in soft drinks is directly responsible for the current increase in human obesity.