Food Switching - Locating Essential Nutrients




Food switching is a mechanism in mammals that enables them to locate essential nutrients in their environment.


Neuroscientists working separately at the University of California at Davis and at New York University School of Medicine have revealed a 'food switching' behavior 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 is 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 binge on large quantities of fat and sugar - so that people might take notice.  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 Food Switching Signal

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.


Dorothy Gietzen of the University of California at Davis has found similar results in rats, mice, even slugs. When Gietzen knocked out the gene that serves up the critical enzyme switch, the animals continued to eat foods that lacked nutrition. Animals who had not been tampered with waited for something more nutritious to come along.


"If the amino acid is not there, they won't eat the diet," said Gietzen, who published her most recent results in the journal Science. "Their brains recognized that their diet was not good for them."


The problem is there are other, stronger signals that don't always tell us to choose the apple over the candy bar.


"The story goes that in evolution when we didn't have much food around, the instinct to eat food rich in calories was a good signal to have because high-fat foods store well," said Kelley.


Conflict In Signals

Kelley's research has shown that a high-fat diet appears to alter the brain biochemistry through the release of reward signals, in a similar reaction to drugs such as morphine. This is due to the release of opioids - "pleasure chemicals" in the brain - that reduce the feeling of being full.


More studies by Dr. Sarah Leibowitz, a neurobiologist at Rockefeller University in New York, have shown that exposure to fatty foods might reconfigure the hormonal system to want more fat.