The study – published in Cell – describes in detail the complex chain reactions triggered by digesting proteins, which lead to a 'satiety' message being sent to the brain after a meal. The researchers 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 prevention of obesity.
The authors, led by Dr Gilles Mithieux of the Université de Lyon, France, said their results will make it possible to envisage improved strategies for the care of overweight people.
"These findings explain the satiety effect of dietary protein, which is a long-known but unexplained phenomenon," said Mithieux. "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.
The researchers revealed that food intake can be modulated through mu-opioid receptors (MORs) – which also bind morphine – on nerves found in the walls of the major blood vessel that drains blood from the gut (the portal vein).
Specifically, they said, stimulating the receptors enhances food intake, while blocking them suppresses intake.
They found that digested dietary proteins stimulate these MORs, thus 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.
Mithieux noted that 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. He noted that because MORs are also present in the neurons lining the walls of the portal vein in humans, the mechanisms uncovered by the team may also take place in people.
The team says that the challenge is now to determine how to act on the mu-opioid receptors to control the fullness sensation over long periods.
Mithieux revealed that if used too intensely, the receptors may become insensitive: “A means of activating them 'moderately' must be found, thus retaining their long-term beneficial effects on controlling food intake."