Being fat all in the head?

Last updated: Monday, June 09, 2008 Print

Your nerves, rather than your eating habits, may have a more direct role in whether you are fat or thin, according to new research.

A new US study found that levels of serotonin, the nerve-signalling chemical targeted by many antidepressants, 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.

"The nervous system makes a decision about its state leading to effects on behaviour, reproduction, growth and metabolism. These outputs are related, but they are not consequences of each other. It's not that feeding isn't important, but the neural control of fat is distinct from feeding," Ashrafi said.

Serotonin may help the body decide whether to burn off excess calories, or store them as fat.

The findings, published in the journal Cell Metabolism, could lead to better diet drugs and treatments for diseases like diabetes.

Roundworms genetically similar
He worked with roundworms for his experiment, but said the findings may relate to humans. "These worms, although they are microscopic, have around 20 000 genes ... and if you compare them side by side they are about 50 percent similar to us," he said.

Genes controlling appetite, fat storage and metabolism are especially similar, he said. The tiny worms can be manipulated to affect changes to their metabolism, appetite and weight gain.

"It has been known for a long time that increasing serotonin causes fat reduction," Ashrafi said.

The research found serotonin levels affected the worms' appetite, but they also affected how much fat the worms accumulated. This was via a separate process.

Appetite only one aspect
In the worms and in mammals, high serotonin levels are associated with fat reduction, while low serotonin levels lead to fat accumulation, the researchers noted. However, in the worms, when serotonin goes up, the worms' desire to eat increases even as fat melts away. But in humans, high serotonin leads people to eat less and shed fat.

"Different people may have similar diets and 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.

Exercise also a factor
This idea relates to another study last year that claims that regular exercise may work as well as medication in improving symptoms of major depression.

It is a well-known fact that levels of the nervous system chemical serotonin directly link to a person's mental well-being. It is also known that physical exercise causes the body to produce serotonin. The study therefore aimed to prove that psychological well-being can be achieved through regular exercise.

The study, published in the journal Psychosomatic Medicine, included 202 men and women age 40 and older who were diagnosed with major depression. They were randomly assigned to one of four groups: one that worked out in a supervised group setting three times per week; one that exercised at home; one that took the antidepressant sertraline (Zoloft); and one that took placebo pills.

By the end of the study researchers found that 47 percent of patients on the antidepressant no longer met the criteria for major depression. The same was true of 45 percent of those in the supervised exercise group.

In the home-based exercise group, 40 percent went into remission, compared with 31 percent of the placebo group.

How it may work
There are several theories on why exercise might improve depression. For example, physical activity seems to affect some key nervous system chemicals - norepinephrine and serotonin - that are targets of antidepressant drugs. It also affects brain neurotrophins which help protect nerve cells from injury and transmit signals in brain regions related to mood.

Exercise may also boost people's feelings of self-efficacy and promote positive thinking. Some experts speculate that group exercise, with its social aspect, may have added benefits. – (HealthDay News, Reuters Health/Maggie Fox)

June 2008