The University of Florida researchers hypothesized that a high-fructose diet could lead to leptin resistance, which in turn could lead to exacerbated weight gain in the face of a high-fat, high-calorie diet, a typical diet in industrialized countries. To test their hypothesis, the research team performed a study with two groups of rats. They fed both groups the same diet, with one important exception: one group consumed a lot of fructose while the other received no fructose.
Two groups similar over six months
During these six months, there were no differences in food intake, body weight, and body fat between rats on the high-fructose and the rats on the fructose-free diets. In addition, there was no difference between the two groups in the levels of leptin, glucose, cholesterol or insulin found in their blood. There was only one difference at the end of the six months: The rats on the high-fructose diet had higher levels of triglycerides in their blood.
The researchers next tested the animals to see if they were leptin resistant. They injected all the animals with leptin, to see if they would respond by eating less. Animals whose leptin response is functioning normally will lower their food intake. The researchers discovered that the rats on the high-fructose diet were leptin resistant, that is, they did not lower their food intake when given leptin. The no-fructose animals responded normally to leptin by eating less.
This first six months of the study showed that leptin resistance can develop silently. "Usually, leptin resistance is associated with obesity, but in this case, leptin resistance developed without obesity," Shapiro said. "This was very surprising."
Role of diet
Having seen that leptin resistance could develop silently, the researchers next wanted to find out what would happen if they switched the rats to a high-fat, high-calorie diet -- the kind many Americans eat. They
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American Physiological Society