The activity of beneficial bacteria in the digestive system was different in the chocolate fans, too.
"We now know that people's metabolic state is, in part, determined by their tastes and selection of food," Kochhar said. "In itself, this is not surprising. But what we have now is a way of measuring the [imprints] and as such may be able to help people make better food choices in the future."
So, will the research help people avoid being fat? It's not clear yet, Kochhar said, but the research is a "first step" toward manipulating metabolisms to improve health.
The next step, he said, is to look at possible gender differences by studying women and doing more research into how diet can affect the germs in digestive systems.
Kochhar said women weren't included in the first study, because previous research had shown metabolic variations linked to the menstrual cycle. But the researchers plan to include women in future clinical trials on metabolic responses to chocolate to see if there's a gender-based reaction to the candy.
Check an exhibit on the science of chocolate at exploratorium.edu.
SOURCES: Sunil Kochhar, Ph.D., researcher with the Nestlé Research Center, Lausanne, Switzerland; Nov. 2, 2007, Journal of Proteome Research
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