Genome-wide association studies have indicated that a preference for certain tastes can be traced back to genes. New work by scientists at Northwestern University has indicated that people who prefer to drink black coffee also like dark chocolate, and that those who like bitter, black coffee and dark chocolate carry genetic variants that produces those taste preferences, but that those variants cause caffeine to be metabolized faster in those people. The findings have been published in Scientific Reports. The study suggested that for people with those genetic variants, the bitter flavor has been linked to a stimulatory boost that is associated with caffeine consumption.
The gene variants identified in this study don't impact taste, they're related to a faster metabolism of caffeine, said lead study author Marilyn Cornelis, associate professor of preventive medicine in nutrition. "These individuals metabolize caffeine faster, so the stimulating effects wear off faster as well. So, they need to drink more." This effect may simply be a learned one; the bitterness of the flavors is associated with the mental boost, so people seek the food and drink that produces that feeling, Cornelis suggested.
Though dark chocolate does not contain a lot of caffeine, it does carry a molecule related to caffeine called theobromine, which is a psychostimulant.
Decreases in the risk of some disorders have been associated with the consumption of coffee and dark chocolate. Moderate coffee intake has been linked to a lower risk of cardiovascular disease, diabetes, some types of cancer, Parkinson's disease, and type 2 diabetes. Dark chocolate has been associated with a reduction in the risk of heart disease. However, the epidemiological data that produced these conclusions have not found a mechanism underlying the associations, and they are not necessarily related to cause and effect.
Studies that investigate genetic variants could reveal more about whether coffee confers health benefits. For now, it seems the genetic variants that have been linked to a preference for coffee are more likely to be related to markers for people who prefer certain kinds of coffee. These data may confound conclusions about coffee and health.
"Drinking black coffee versus coffee with cream and sugar is very different for your health. The person who wants black coffee is different from a person who wants coffee with cream and sugar. Based on our findings, the person who drinks black coffee also prefers other bitter foods like dark chocolate. So, we are drilling down into a more precise way to measure the actual health benefits of this beverage and other food," Cornelis explained.