Eating 85 percent dark chocolate every day for three weeks lowered negative moods in a randomized trial, and the people who ate it ended up with more varied gut bacteria. The 70 percent chocolate had no clear effect on mood. Seoul National University researchers split 48 healthy adults aged 20 to 30 into three groups. One group ate 30 grams a day of 85 percent dark chocolate, about a third of a standard 100-gram bar. Another ate 30 grams of 70 percent chocolate, and the third ate none. The study appeared in the Journal of Nutritional Biochemistry. Mood was tracked with a standard questionnaire that measures good and bad feelings, such as feeling upset, nervous, or irritable. After three weeks, bad feelings dropped in the 85 percent group, and the 70 percent group showed no clear change. Stool samples from the 85 percent group showed a wider variety of gut bacteria than the no-chocolate group. One type, Blautia obeum, went up, and another, Faecalibacterium prausnitzii, went down. People whose gut bacteria became more varied, and whose Blautia obeum rose the most, had the biggest drops in bad mood. Dark chocolate may work like food for certain gut bacteria, the researchers suggest, and those bacteria could affect mood through the connection between the gut and the brain. Each group had only 14 to 18 people, and the link between bacteria and mood is a correlation. In this trial, the darker chocolate lowered bad moods within three weeks, and the milder one left mood about where it started.