'Eat Right' Enzyme Directs Healthy Eating

April 13, 2005 — -- We shouldn't need our mothers to tell us to finish our vegetables -- research shows our bodies are wired to let us know.

Neuroscientists working separately at the University of California at Davis and at New York University School of Medicine have revealed an ancient "switch" in some mammals that signals the appetite to seek foods with perfect nutritional balance.

The mechanism has been found in rats, mice, slugs, even yeast and, the researchers say, there's every reason to believe it also exists in people.

"It's a very simple mechanism that's present in very simple organisms," said David Ron of the New York University School of Medicine. "When you see that in biology it usually means it's an important mechanism that's present in all species, including humans."

The trick is finding a way to emphasize that switch over less-healthy ones -- like the impulse to scarf down large quantities of fat and sugar -- so that people might listen to it more diligently. As researchers point out, the signal to eat good nutrition is only one of a wide array of signals at play when it comes to appetite.

"Food intake is complicated," said Ann Kelley, a neuroscientist at the University of Wisconsin at Madison. "There are so many molecules in the brain that turn it on and off that no one has a clear definitive idea of how it all works."

The switch for eating good nutrition is not a single mechanism, but a cascade of events that starts with an enzyme known as GCN2 kinase. When eating a food that's deficient in one of the 20 critical amino acids (the building blocks that make up proteins), the body detects the deficiency in the bloodstream and puts the brakes on appetite. This prevents the animal from eating too much of one thing -- say corn, which lacks the amino acid tryptophan, and triggers more foraging for foods that can complete their nutritional needs.

"This tells us that we have an innate mechanism for recognizing what's good for us to eat," said Ron, who published his results in the current issue of the journal Cell Metabolism.