FRIDAY, May 24, 2002 (HealthDayNews) -- Just standing in front of a plate of food could make you gain weight.
Researchers at the U.S. Department of Energy's Brookhaven National Laboratory have found that showing foods to individuals caused a significant elevation in brain dopamine, the neurotransmitter that is associated with motivation and reward -- and also addiction.
While sniffing or salivating over your favorite caviar may not actually cause the calories to accrue, it could send a message to your brain urging you to eat.
The study, which appears in the June 1 issue of the journal Synapse, represents the first time researchers have shown the human dopamine system can be triggered by food even when there's no eating involved.
The researchers also found that looking at food activated the dopamine-motivation circuit in a different way than actually eating did. This may be closer to what happens when drug addicts experience a craving.
Although this particular study looked at normal-weight individuals, the findings could have enormous implications for a society plagued by obesity.
"We are overburdened by food stimuli, which, whether you like it or not, are liberating dopamine and telling us to go get this food," says Dr. Nora Volkow, the study's lead investigator and the associate laboratory director at Brookhaven in charge of life sciences. "If we can figure out a way of interfering with the dopamine responses then we would be able to control the urge to eat when exposed to food stimuli."
In this study, the researchers injected 10 healthy volunteers with a radiotracer (or radioactive "tag") that binds to dopamine receptors in the brain. Once the tag binds to the receptors, the chemical dopamine is prevented from "docking," so to speak. It's then possible to measure changes in dopamine levels with positron emission tomography (PET).
The volunteers' brains were scanned both without food stimulation and after they were shown foods they had earlier identified as their favorites. In what could be seen as a form of gastronomic torture, those foods were warmed to enhance the aroma and participants were allowed to taste a tiny portion dabbed on a cotton ball and placed in their mouths.
Participants were also scanned with and without methylphenidate (Ritalin), which blocks the reabsorption of dopamine into nerve cells. The elevation in dopamine occurred when food stimulation was combined with the methylphenidate. What's more, the dopamine increase took place in the dorsal striatum, an area of the brain not previously known to be involved in food motivation. The combination of food stimulation and methylphenidate was also linked to changes in participants' reports of feeling hungry.
Until now, scientists thought the nucleus accumbens, a part of the brain located in the ventral striatum, was responsible for food reward.
Other scientists feel the results, while interesting, are hardly earth-shattering.
"There is a little effect, and it's compatible with the idea that dopamine is involved with eating," says Dr. Richard Wurtman, a professor of neuroscience at the Massachusetts Institute of Technology.
However, researchers have long known the dorsal striatum is involved in initiating behavior.
"Whenever people decide to do anything there tends to be a release of dopamine. It makes sense that if someone sees food and thinks about getting some food, dopamine release would go up," Wurtman says. "It's not really a food part of the brain. It's involved in initiating behavior, and that includes eating behaviors."
Volkow's next step is to see if people do indeed act on this message from the brain.
"Normal-weight people have these responses, and they're able to control it in such a way that their weight is proper. The next step is to study people who cannot control it, and have no ability to restrain from eating," she says. "A compulsive eater, when exposed to food, has to have it. We want to understand if this is because the dopamine system is much more sensitive and, if it is, what sort of interventions can we do to change that."
What To Do: For guidance on how to eat right, visit the American Dietetic Association. For more information on addiction research, go to Brookhaven National Laboratory.
