In a study out of the Sanford-Burnham Medical Research Institute, (Sanford-Burnham) researchers found that a brain chemical called orexin may be responsible for activating the calorie-burning form of fat called brown fat. Results may help solve why some people gain weight and others don’t despite what they eat.
Brain Hormone Orexin and Obesity
Orexins, also referred to as hypocretins, are the name given to a pair of excitatory neuropeptide hormones found in all major classes of vertebrates. They were discovered simultaneously by two groups of researchers in rat brains. Orexin has been found to stimulate feeding and arousal. A deficiency is linked to narcolepsy, a sleep disorder associated with obesity, and paradoxically with reduced food intake.
White Fat Stores, Brown Fat Burns
While most people are familiar with white fat, they probably don't know about brown which does more than store fat, it burns it. Writes researcher Patrick Seale about the function of orexin in his report, “Orexin Turns Up the Heat on Obesity,” “Brown adipocytes burn chemical energy to produce heat for protection against hypothermia and obesity. Sellayah et al now reveal that a secreted neuropeptide, Orexin, functions a key driver of brown adipocyte differentiation through direct actions on brown adipose precursors.”
Scientists once believed brown fat, primarily stored between the shoulder blades along the vertebrae and over the heart, disappeared after infancy, yet recent advances in imaging technology discovered brown fat in humans. The level of orexin in a person’s body is believed to be ruled by heredity.
Scientists aren’t aware of any other substance in the body that activates brown fat or stimulates the brain to make more orexin. The jury is still out, some scientists believe, on the degree to which orexin plays a role in weight. “The idea of burning excess calories by generating more brown-fat is still being debated, says Dr. Carey Lumeng, an adipose-tissue researcher and assistant professor of pediatrics at University of Michigan in an article for the Orlando Sentinel. “A lot still needs to be explored, but my sense is that it will play a role, but it won’t be the only solution,” he says.
Orexin Activates Brown Fat to Burn Calories
Brown fat is loaded with mitochondria and blood vessels which accounts for its color, and does a good job converting calories into energy, a process that appears not to function well in people who are obese.
Sanford-Burnham researchers found in their study that orexin activated calorie-burning brown fat in mice. Obesity may be due in some people, to an impairment in brown-fat thermogenesis, how heat is produced and generated, a process integral to body weight regulation.
Scientists studied mice that weighed more than their normal counterparts but actually consumed less food, suggesting that overeating didn’t cause their obesity, that something else was going on. The obese mice, it turns out, were orexin-deficient which reduced thermogenesis (heat production). When the obese mice were fed a high-fat diet their body didn’t get rid of the extra calories as heat the way the normal-sized mice did; the obese mice (and people) deficient in orexin stored the energy as fat.
Researchers believe the mice lacking orexin didn’t develop properly at the embryonic stage which effected how their body expended energy and gained weight even into adulthood. “Our study provides a possible reason why some people are overweight or obese despite the fact that they don’t overeat—they might lack the orexin necessary to activate brown fat and increase energy expenditure,” explained Devanjan Sikder, D.V.M, Ph.D., senior author of the study and assistant professor in Sanford-Burnham’s Diabetes and Obesity Research Center,
Orexin and Controlling Type 2 Diabetes, Heart Disease and Certain Cancers
Because a deficiency in orexin is linked to obesity, findings suggest orexin supplementation may offer a new therapeutic approach for the treatment of obesity and other metabolic disorders. About one-third of U.S. adults (33.8 percent) are obese, according to the Centers for Disease Control and Prevention, putting them at increased risk for type 2 diabetes, coronary heart disease, stroke, and certain cancers.
While most weight loss medications work to lower a person’s appetite, an orexin-based approach would focus on peripheral fat-burning tissue rather than the brain’s appetite control center.
“Controlling obesity by controlling hunger doesn’t work because the body has ways of compensating,” says Dr. Devanjan Skiler, senior author on the study for the Institute. “Orexin doesn’t control hunger it uses excess calories. The agent is different from others because it will let you eat and lose.”
Sources
“Fighting Fat with Fat.” Beaker: A Medical Research Blog by Sanford-Burnham.(October 4, 2011) (Last last visited: October 4, 2011).
Seale, Patrick, “Orexin Turns Up the Heat on Obesity.” Cell Metabolism. Volume 14, Issue 4, 5 October 2011, Pages 441-442.
Sellayah, Dyan, Bharaj, Preeti, and Sikder, Devanjan Sikder. “Orexin Is Required for Brown Adipose Tissue Development, Differentiation, and Function.” Cell Metabolism. Volume 14, Issue 4, 478-490, 5 October 2011.
Laura Owens - Laura Owens has a B.S. in Psychology from Rollins College & U of FL. She is a freelance writer with expertise in motivation & wellness.
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