Consuming too much fructose will encourage weight gain, and not just because this simple sugar contains calories.
According to a recent study by scientists at the University of Florida College of Medicine in Gainesville, fructose, found in tree fruits, melons and root vegetables such as beets and sweet potatoes, promotes leptin resistance, a condition that makes the brain insensitive to the hormone leptin, which produces the "I'm full" feeling.
Other studies have shown that leptin resistance can lead to rapid weight gain. If you're leptin-resistant you'll stay hungry longer, which may cause you to eat too much. You'll probably consume a lot of white sugar and high-fructose corn syrup, two ingredients now widespread in our diet that both contain a lot of fructose.
Thus you'll find yourself in a cycle — because you're leptin-resistant, you're likely to eat more fructose, and the fructose will make you more leptin-resistant.
The UF researchers fed two groups of rats similar diets with one exception — one group received food containing about 60 percent fructose while the other received no fructose at all.
After six months the rats showed no difference in body weight or body fat, and both groups produced the same amount of leptin. However, the rats on the high-fructose diet had higher levels of triglycerides in their blood and proved to be leptin-resistant. When injected with leptin they did not reduce their food intake as did the rats fed a fructose-free diet.
When the two groups of rats were placed on a tasty high-fat diet, the leptin-resistant rats gained a large amount of weight, almost all of it fat, while the other rats gained only a little.
"This study shows that fructose changes your metabolism," said Philip J. Scarpace, a professor of pharmacology and therapeutics at the UF College of Medicine and one of the authors of the study. "It changes the way your body defends itself against a high-calorie diet."
Scarpace suspects that the high triglycerides in the blood of the rats fed a high-fructose diet somehow prevented the uptake of leptin by the brain
"And if leptin is not working, you'll eat more," he said. "It's not hunger. It's like when we go out for ice cream after dinner. We don't eat the ice cream because we're hungry, or because we need the calories. We eat it because we enjoy it. When leptin is not working properly, rats will continue to consume a tasty diet. They'll eat more. Leptin is important for adapting to a tasty diet."
Freelance writer Tom Valeo writes about medical and health issues.
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