July 6, 2012
Why A Protein Meal Tells Your Brain You're Full
Feeling full involves more than just the uncomfortable sensation that your waistband is getting tight. Investigators reporting online on July 5th in the Cell Press journal Cell have now mapped out the signals that travel between your gut and your brain to generate the feeling of satiety after eating a protein-rich meal. Understanding this back and forth loop between the brain and gut may pave the way for future approaches in the treatment and/or prevention of obesity.
Although levels of fats and sugars have been shown to influence the desire to eat, until now no team had demonstrated how protein molecules regulate appetite.
Food intake can be modulated through mu-opioid receptors (MORs, which also bind morphine) on nerves found in the walls of the portal vein, the major blood vessel that drains blood from the gut. Specifically, stimulating the receptors enhances food intake, while blocking them suppresses intake. Investigators have now found that peptides, the products of digested dietary proteins, block MORs, curbing appetite. The peptides send signals to the brain that are then transmitted back to the gut to stimulate the intestine to release glucose, suppressing the desire to eat.
Mice that were genetically engineered to lack MORs did not carry out this release of glucose, nor did they show signs of 'feeling full', after eating high-protein foods. Giving them MOR stimulators or inhibitors did not affect their food intake, unlike normal mice.
Higher levels of leucine in the hypothalamus fools the brain into believing that there is an ample supply of protein molecules circulating as available fuel in the body. This tricks the brain into suppressing hunger.
Because MORs are also present in the neurons lining the walls of the portal vein in humans, the mechanisms uncovered here may also take place in people.
"These findings explain the satiety effect of dietary protein, which is a long-known but unexplained phenomenon," says senior author Dr. Gilles Mithieux of the Universite de Lyon, in France. "They provide a novel understanding of the control of food intake and of hunger sensations, which may offer novel approaches to treat obesity in the future," he adds.
April McCarthy is a community journalist playing an active role reporting and analyzing world events to advance our health and eco-friendly initiatives.