Creating rats with no fat.

Healthy rats with no visible body fat have been created by University of Texas Southwestern Medical Center at Dallas scientists. Using gene therapy, they made the animals' bodies manufacture 20 times the normal amount of the fat-controlling hormone leptin by using a virus to insert the leptin gene. The rodents' insulin levels dropped by more than half, yet they did not develop diabetes. This finding is in contrast to another study that suggested high leptin levels might cause diabetes.

"This is the first time that animals have been produced which are free of body fat, yet remain in perfect health," notes Kazunori Koyama, a research fellow in internal medicine and one of the authors of the study. "In other conditions of extreme thinness and rat loss--like starvation, severe diabetes, or severe hyperthyroidism--the animals also lose lean body mass. But not in these; they selectively lose fat."

Researchers hope these findings will help them determine what role fat plays in various bodily functions and diseases, including type II diabetes (non-insulin dependent diabetes mellitus), which often affects obese adults.

Robert O'Doherty, another of the study's authors and a fellow in biochemistry, cautions: "This is not a treatment for human obesity. We don't yet know the long-term effects of leptin. Also, obese people already have high leptin levels. The reason they are not losing weight may be that they are resistant to...