A new study, published in the journal Helion by Vanderbilt University, has revealed that obesity may be caused by defective signaling in the brain upon overeating of high fat foods.
Obesity has become a global chronic health problem with statistics specifying that approximately two billion people are overweight, and 600 million of these are obese.
“We have always been struck by how much animals — and even people — will over-consume tasty high-fat foods, even though they might be technically feeling full,” said Dr. Aurelio Galli, one of the authors of the study. “A high fat diet causes people to eat more, which ultimately impairs the ability of obese people to successfully control their caloric intake, lose weight and maintain weight loss. We have conducted several studies trying to understand why a high fat diet has this effect.”
The researchers identified a new metabolic mechanism behind overeating high fat foods for pleasure. A specific signaling pathway in brain cells that control motivation, movement and attention determines the amount of high fat foods consumed. When the signaling is defective, the person only overeats high fat foods.
“We distilled the neurobiological mechanisms involved specifically in overeating for fat,” said Dr. Kevin Niswender, one of the authors of the study. “We defined the why, where, and how of ‘hedonic’ obesity and found that disrupting a specific signaling pathway in the brain can lead to overeating specifically food high in fat.”
Mice were genetically altered by removing the Rapamycin complex 2 (mTORC2; a group of proteins involved in insulin signaling in the brain. Mice without a functioning mTORC2 ate high-fat food excessively; when provided only with low-fat food they did not overeat.
“Our findings reveal a system that is designed to control eating of rewarding foods that are high in fat and possibly sugar,” said Dr. Galli. “This system can be hijacked by the very foods that it is designed to control. Eating a high-fat or high-carbohydrate diet feels rewarding, but also appears to cause changes in the brain areas that are involved in controlling eating, by causing for example insulin resistance. Our study shows that when specific signaling in these areas of the brain is disrupted, it leads to a vicious cycle of increasing, escalating high-fat diet intake that likely further cements changes in these brain areas.”
Aurelio Galli et al. Impaired mTORC2 signaling in catecholaminergic neurons exaggerates high fat diet-induced hyperphagia. Heliyon, 2015 DOI: 10.1016/j.heliyon.2015.e00025