The sweetener fructose, which is found in many foods, has been found to cause leptin resistance, thus directly linking it to weight gain and obesity.
Alexandra Shapiro, Philip J Scarpace, and colleagues at the University of Florida College of Medicine studied two groups of rats for six-months. Both groups were fed the same diet, except one of the groups was also given fructose. During those six-months the researchers noted no difference in food intake, body weight, and body fat, between the two groups of animals. Furthermore, there were no differences in leptin, glucose, cholesterol or insulin levels. In fact, the only difference the researchers found was that the rats fed fructose had higher triglyceride levels by the end of the six-month period.
The researchers then injected both groups of animals with leptin. Theoretically, both groups of rats should have responded by eating less. However, what they found was that the rats fed fructose had become leptin resistant, and therefore did not alter their food intake, whereas the rats who were not fed fructose began to eat less as expected. They then switched both groups of animals to a high-calorie, high-fat diet. Those fed fructose ate more and gained significantly more weight and fat than the animals fed a fructose-free diet.
In a news release issued by the University of Florida, study co-author Phillip J Scarpace, a professor of pharmacology and therapeutics, said: "If these findings are applicable to humans, then there could be consequences of eating a diet high in fructose, but only if you also consume an excessive amount of calories. If you go on a trip, attend a celebration, or otherwise eat more than you usually eat, a person consuming a low-fructose diet may be able to handle it. But the individual who has set themselves up so that leptin no longer works will be unable to burn the extra calories, and now they gain a lot of weight."
Shapiro A, Mu W, Roncal CA, Cheng KY, Johnson RJ, Scarpace PJ. Fructose-induced leptin resistance exacerbates weight gain in response to subsequent high fat feeding. Am J Physiol Regulatory Integrative Comp Physiol. 2008; doi:10.1152/ajpregu.00195.2008.
News release: Fructose hampers hormone that controls appetite, UF study finds. University of Florida Website. October 16th 2008.