How fat might be managed through the nervous system

June 9, 2008

Disabling the vagus nerve slows down energy storage in fat tissue. Another surgery may make the body burn fat faster.

Such a procedure would target the sympathetic nervous system, which regulates fat burning -- as opposed to the parasympathetic nervous system (including the vagus nerve), which regulates energy storage. Some researchers believe that stimulating certain sympathetic nerves could promote weight loss by burning off more calories from fat tissue. "It is like getting the effect of exercise without having to do real exercise," says Dr. Jiande Chen, a gastroenterologist at the University of Texas Medical Branch at Galveston.

Clinical evidence for this idea is lacking, Chen cautions, but indirect support comes from studies on dogs, cats, rabbits and other animals. For instance, in a 1998 study on hamsters at Georgia State University in Atlanta, Timothy Bartness and co-workers found that cutting the sympathetic nerves to part of an animal's fat tissues prevented its body from burning up the energy stored there. Unlike the remaining fat tissues, the "denervated" tissue did not shrink even when food intake was decreased. This suggests that stimulating the nerves instead could have the opposite effect -- of promoting fat burning.

Inspired by this possibility, Brooklyn Center, Minn.-based Leptos Biomedical is building a pacemaker-like electronic device designed to stimulate sympathetic nerves in specific fat tissues in the body. In addition to shrinking these tissues, the therapy may cause patients to feel fuller and less hungry, says Kobi Iki, vice president of research at the company. Animal studies show that the method produces consistent weight loss, reduced food intake and an increase in the muscle-to-fat ratio, Iki says, and the company is currently preparing for human trials of the method.

Although much more speculative as a therapy for obesity than vagotomy or vagal nerve blocking, sympathetic nerve stimulation has a potential advantage over them. By allowing the surgeon to choose which sympathetic nerves to stimulate, it offers the possibility of targeted weight loss. Thus the technique could be used to get rid of "bad" fat around organs while sparing fat elsewhere in the body, according to Dr. Ken Fujioka, an endocrinologist and principal investigator of the VBLOC trial at Scripps Clinic in La Jolla, and a consultant for Leptos. "If you can target abdominal fat, that is really the Holy Grail right now."

-- Chandra Shekhar