Born to Be Obese?

TUESDAY, Feb. 5 (HealthDay News) -- The brain circuitry that controls appetite might be wired differently in some people, and that could predispose them to obesity, California researchers suggest.

The study was conducted in rats, not humans, and yet it could ultimately lead to novel obesity treatments, said Philip Smith, director of the Office of Obesity Research at the National Institute of Diabetes and Digestive and Kidney Diseases.

"It is not just about drugs that modify short-term appetite," he said, "there may be drugs that stimulate development of the appropriate neural pathways. So, it is an exciting, but very early, time in this field."

The study was published in the February issue ofCell Metabolism.

Sebastien Bouret, an assistant professor of neuroscience at the University of Southern California, and his colleagues examined neural circuits emanating from the appetite, hunger and body-weight control center of the brain -- the so-called arcuate nucleus of the hypothalamus (ARH) -- in a series of rats bred to be either prone to, or resistant to, obesity.

The team found fewer neural connections projecting from the ARH in obesity-prone animals than in their leaner counterparts. Surprisingly, Bouret said, this deficiency developed very early in life, before the animals became obese, and appeared to extend into adulthood.

"Somehow, these animals are programmed to become obese," Bouret said. "The obesity is hard-wired into the brain."

When the researchers then looked at why the brains of obese rats differed from their normal-weight counterparts, they found that the neurons from obesity-prone animals were less responsive to leptin, a hormone that controls the development of these circuits, and which also signals the body's energy status and controls metabolic rate.

"This paper presumes to say, these animals must be leptin-resistant, and that is why the pathways are not developing," said Smith.

But that doesn't mean they are doomed to a life of severe obesity, said Dr. Barbara Kahn, chief of the Division of Endocrinology, Diabetes and Metabolism at Beth Israel Deaconess Medical Center, in Boston. How they live their lives also matters.

"It is important not to 'blame' the obese person or imply that he/she is responsible for being obese," Kahn noted. "Having said that, reasonable, healthy caloric restriction and a safe and sustainable program of physical activity can help limit weight gain and often bring about some degree of weight loss. In addition, healthy eating and regular exercise can reduce the complications of obesity such as type 2 diabetes and cardiovascular disease."

At the same time, she added, not everyone can wear a size 4.