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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. |
