Researchers have uncovered new evidence to explain the observation that diets rich
in protein stunt the appetite, according to a report in the November Cell Metabolism.
The findings suggest a novel link connecting macronutrients in the diet to hunger, the
researchers said. The results also point to a potential new target for the treatment of
eating disorders, they added.
"It is well known that protein feeding decreases hunger sensation and subsequent
food intake in animals and humans," said study author Gilles Mithieux of INSERM and
Universite Lyon in France. However, the mechanism by which proteins exert their
control over appetite remained unclear, the researchers said. In fact, earlier studies
have found that a rise in dietary protein shows little effect on the major hormones that
regulate hunger, they added.
In a study of rats, Mithieux and colleagues made the surprising discovery that diets
heavy in protein spark the production of glucose in the small intestine. That rise in
glucose, sensed in the liver and relayed to the brain, led the animals to eat less, they
reported.The current findings provide an answer to the question of how
protein-enriched meals decrease hunger and reduce eating, unsolved up to now,"
according to the researchers. "Our data also brings to light a novel concept of control
of food intake, involving the small intestine glucose metabolism as a key relay from
the macronutrient composition of the diet to the amount of food ingested." The group
found that protein feeding of rats markedly increased the activity of genes involved in
glucose production in the animals' small intestine. Those activities led to glucose
synthesis and release into the portal vein--the vessel that conducts blood from
digestive and other organs to the liver--a phenomenon lasting after the assimilation of
glucose from the diet.
Furthermore, they found that the flux in glucose detected by the liver glucose sensor
activated parts of the brain involved in the control of appetite, causing a decline in
subsequent food consumption.
"In addition to protein's ability to diminish appetite, it had also been suggested that
glucose appearance in the portal vein, as occurs during meal assimilation, may
induce comparable consequences," Mithieux said. "Here, we connect these previous
observations by reporting that intestinal synthesis of glucose is induced following
food digestion in rats specifically fed a protein-enriched diet."
"As in rats, diets high in protein suppress appetite in people," the researchers
added. The human intestine also synthesizes glucose. "Therefore, glucose
metabolism in the small intestine may be a new target in the treatment of food intake
disorders," they said.
NEWSLETTER of May 2009
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