The team of researchers was led by Sunil Kochhar, PhD, who heads the BioAnalytical Science Department at the Nestlé Research Center in Switzerland. He and his colleagues designed the study to see whether eating dark chocolate every day for two weeks could affect the way the body metabolizes stress hormones.
They recruited 30 healthy young people—11 men and 19 women. They tested their anxiety levels and determined that 13 of them tested as “high anxiety” and 17 tested as “low anxiety” on standardized anxiety tests. They gave the volunteers 40 grams of dark chocolate (about an ounce and a half), containing 74% cocoa, every day for two weeks and tested their blood and urine at the beginning and end of the trial.
In the high anxiety group, eating chocolate reduced levels of their stress hormones, and the changes were “biologically significant,” Dr. Kochhar tells me. What’s more, people felt less anxious after munching on chocolate. The findings did not apply to the low anxiety group. “We observed improvement in the anxiety states of subjects immediately after their consumption of chocolate,” he says.
Though the product used in the study, Nestlé Noir Intense, is not available in the United States, Dr. Kochhar tells me that any dark chocolate with a cocoa content of more than 60% is likely to have the same benefits. We know from other chocolate studies that the darker the chocolate (the higher its cocoa content), the more health benefits it offers.
Though the participants consumed about 220 extra calories a day, they didn’t experience measurable changes in blood-sugar levels. But if you’re thinking about regularly eating this much dark chocolate, better trim 220 calories elsewhere, or you could find yourself 23 pounds heavier a year from now.