Beta Adrenergic Receptors Control Weight Gain

Researchers have found that beta adrenergic receptors (betaARs ) are necessary for diet-induced thermogenesis, and that this efferent pathway plays a critical role in the body's defense against diet-induced obesity. Their findings were published in the August 2, 2002, issue of Science.

To study the role of betaARs, investigators at Beth Israel Deaconess Medical Center (Boston, MA, USA) developed a strain of mice lacking all three known betaARs (beta-less mice). Over an eight-week period, the researchers compared the beta-less mice with a group of controls as the two groups were fed different diets: the first, a bland diet of standard rodent food and the second, a high-calorie diet enriched with fat and sugar.

Beta-less mice on the standard diet had a reduced metabolic rate and were slightly obese. On the high-fat diet, beta-less mice, in contrast to the control mice, developed massive obesity, gaining 26 g compared with only seven grams among the control mice. The massive obesity was due entirely to a failure of diet-induced thermogenesis. The difference in weight gain was not related to the amount of food that was consumed, since animals in both groups ate about the same amount. The difference was that the control mice converted excess calories to heat while the beta-less mice were unable to eliminate the fat by this route.

Dr. Bradford B. Lowell, of the department of endocrinology and senior author of the study explained, "In the control mice, it was clear that a process was ‘switched on' as soon as they were fed diets high in fat and calories. The betaAR pathway has been proposed to exist for many years, but previous research was unsuccessful in proving its importance for diet-induced thermogenesis. In this study, we have done something more selective by creating genetically engineered mice with no capability at all for betaAR action. These findings indicate not only that beta adrenergic receptors are necessary for the process of diet-induced thermogenesis, but that the process has an important role in preventing obesity.”