Fructose may exacerbate obesity with high-fat diet

The study claims to be the first to report that high fructose consumption can lead to leptin resistance. Leptin is a hormone that plays a role in helping the body to balance food intake with energy expenditure.

Researchers from the University of Florida report their findings in the American Journal of Physiology ​–​ Regulatory, Integrative and Comparative Physiology​.

The study also claims to be the first to show for the first time that leptin resistance can develop silently, with little indication that it is happening.

“This study may explain how the global increase in fructose consumption is related to the current obesity epidemic,”​ said lead author Alexandra Shapiro.

An estimated 25.6 percent of US adults reported being obese in 2007, compared to 23.9 percent in 2005 which is an increase of 1.7 percent, according to a study published in Morbidity and Mortality Weekly Report​ last month.

Study details​

The Florida-based researchers performed a study with two groups of rats. Both groups were fed the same diet, but one group’s diet contained more of fructose while the other received no fructose.

Over the course of the six months of the experiment, the researchers failed to notice any differences between the groups regarding food intake, body weight, and body fat. Moreover, no differences were observed between the two groups for blood levels of leptin, glucose, cholesterol or insulin. Only difference was observed, and this was that rats on the high-fructose diet had higher blood levels of triglycerides.

Subsequent testing of the animals to see if they were leptin resistant revealed that the rats on the high-fructose diet were leptin resistant

“Usually, leptin resistance is associated with obesity, but in this case, leptin resistance developed without obesity,”​ said Shapiro. “This was very surprising.”​

American diet​

The next stage in the research was to test the effects of the high fructose consumption when eaten in combination with a high-fat, high-calorie diet, similar to a ‘typical’ Americans diet.

Shapiro and her co-workers found that the animals exposed to the high-fructose diet, the leptin resistant rats, had higher food intakes than their leptin responsive counterparts on the fructose-free diet.

Mechanism​

By means of explaining the mechanism behind the observations, the researchers suggested that elevated triglycerides may impair the transport of leptin across the blood brain barrier. This would inhibit the brain’s signaling to stop eating.

“The presence of high fructose alters the way leptin works, fooling the brain so that it ignores leptin,”​ said co-researcher Philip Scarpace.

The research was funded by the National Institutes of Health

Source: American Journal of Physiology ​–​ Regulatory, Integrative and Comparative Physiology​Published online ahead of print, doi:10.1152/ajpregu.00195.2008“Fructose-induced leptin resistance exacerbates weight gain in response to subsequent high-fat feeding”​Authors: A. Shapiro, W. Mu, C. Roncal, K.-Y. Cheng, R.J. Johnson, P. J. Scarpace