Why some diets fail...
2008-06-04 09:31
Washington - A brain chemical
strongly linked to mood and appetite may also directly affect
fat gain, US researchers reported on Tuesday.
They said levels of serotonin, the nerve-signalling chemical
targeted by many anti-depressants, may also direct the body to
put down fat regardless of how much food is eaten.
"It may be one reason diets fail," metabolism expert Kaveh Ashrafi of the University of California, San Francisco, who led the study, said in a telephone interview.
The findings, published in the journal Cell Metabolism,
could lead to better diet drugs and treatments for diseases
like diabetes.
Serotonin may help the body decide whether to burn off
excess calories, or store them as fat, Ashrafi said.
He worked with roundworms for his experiment but said the
findings may relate to humans. "These worms, although they are microscopic, they have around 20 000 genes ... and if you compare them side by side they are about 50% similar to us," he said.
Genes controlling appetite, fat storage and metabolism are
especially similar, he said. The tiny worms can be manipulated
to see changes to their metabolism, appetite and weight gain.
"It has been known for a long time that increasing
serotonin causes fat reduction," Ashrafi said.
"At the molecular level we are trying to understand what is
the mechanism that allows that to happen. What we discovered in
the worm is that those mechanisms can be separated from the
mechanisms that mediate the effects of serotonin on appetite."
The research found serotonin levels affected the worms'
appetite, but they also affected how much fat the worms
accumulated, and this was via a separate process.
If the worms detect a food shortage, their metabolisms
shift and they store more fat. This could explain why some
people get fat more easily than others - and why dieting can
cause more weight gain later.
"Different people may have similar diets, may have similar
rates of physical activity, but may have very different body
weights," Ashrafi said. "Appetite is only part of it."
But for now the remedy for excess body fat remains obvious.
"Nothing in our study says that good nutrition and physical
activity are not good for you," Ashrafi said.
Simply raising serotonin levels can have serious
side-effects. The diet drug fenfluramine, which has the effect
of raising serotonin levels, was pulled off the market in 1997
after it caused sometimes deadly heart valve damage.