Fructose Increases Obesity

A new study found that consumption of fructose increased body weight despite a reduction in calories.

In the study, researchers at the University of Cincinnati allowed mice to freely consume either plain water or fructose-sweetened water and soft drinks. The mice that drank the fructose-sweetened water and soft drinks gained weight, even though they took in fewer calories from solid food. By the end of the study, the mice that consumed fructose-sweetened beverages had 90 percent more body fat than the mice that consumed water only.

I have been opposed to fructose for a while. In fact, I often advise against high-sugar fruits in an effort to avoid fructose. The liver isn't able to metabolize fructose for energy in the same that it does other sugars, so the fructose is converted to triglycerides and immediately stored as fat. Until now, it was assumed that the fructose would be burned for energy fairly quickly (after being converted to triglycerides), but this study suggests that even with a caloric deficit the body will store fructose as fat.

Bottom line: Avoid ALL sweetened soft drinks and fruit juices. Also make an effort to limit high-sugar fruits like oranges and bananas, and if you must eat them, do so earlier in the day when metabolism is running at its highest.

UPDATE:
An article on Science Daily has a little more info on this topic.

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.