Fructose Sets Table For Weight Gain Without Warning

Eating too much fructose can induce leptin resistance, a condition that can easily lead to becoming overweight when combined with a high-fat, high-calorie diet, according to a new study with rats.

Although previous studies have shown that being leptin resistant can lead to rapid weight gain on a high-fat, high-calorie diet, this is the first study to show that leptin resistance can develop as a result of high fructose consumption. The study also showed for the first time that leptin resistance can develop silently, that is, with little indication that it is happening.

The study, “Fructose-induced leptin resistance exacerbates weight gain in response to subsequent high-fat feeding,” was carried out by Alexandra Shapiro, Wei Mu, Carlos Roncal, Kit-Yan Cheng, Richard J. Johnson and Philip J. Scarpace, all at the University of Florida College of Medicine in Gainesville. The study appears in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, published by The American Physiological Society.

Leptin as regulator

Leptin is a hormone that plays a role in helping the body to balance food intake with energy expenditure. When leptin isn’t working - that is, when the body no longer responds to the leptin it produces - it’s called leptin resistance. Leptin resistance is associated with weight gain and obesity in the face of a high-fat, high-calorie diet.

Obesity has been a growing problem in the U.S. and in other parts of the world and fructose has been suspected of playing a role. Fructose is the sugar found in fruit, but it’s not the normal consumption of fruit that is the problem. Table sugar and high-fructose corn syrup are about 50% fructose and these ingredients have become increasingly common in many foods and beverages. With sugar and high-fructose corn syrup being added to many foods, people now eat much more fructose than ever before.

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.