Does dark chocolate impact mood and emotions via the microbiome? Original paper

Research from clinical trials suggests that cocoa has beneficial effects on mood.^[1] The mechanism responsible for this effect is unclear, although one potential mediator could be the microbiome because cocoa is rich in various compounds (namely, fiber and polyphenols) known to modulate the microbiome, and preliminary research indicates that the microbiome may influence mood and mental health.

This 3-week randomized controlled trial assessed the effects of dark chocolate on mood and gut microbial composition in 48 healthy adults (ages 20 to 30). The participants were randomly assigned to consume 70% dark chocolate, 85% dark chocolate, or no chocolate (control group). Both dark chocolate groups consumed 30 grams of chocolate daily, divided into 10-gram portions consumed in the morning, afternoon, and evening.

The outcomes assessed were positive and negative affect (feelings and emotion), both of which were measured using the Positive and Negative Affect Schedule (PANAS), a questionnaire that measures self-reported feelings and emotions. The investigators also assessed gut microbiota diversity and composition using 16S rRNA sequencing (a genetics-based technique for identifications of microbes).

Compared to the control group, there was a decrease in negative affect in the 85% dark chocolate group. There were no differences between groups for positive affect.

Based on the differences in negative affect, the control and 85% dark chocolate groups were compared for differences in microbiota. The alpha diversity of the microbiome in the 85% dark chocolate group increased according to 2 out of 3 metrics. Among specific gut bacteria species, the 85% dark chocolate group had increased levels of Blautia obeum and decreased levels of Faecalibacterium prausnitzii. The Firmicutes/Bacteroidetes ratio did not differ between groups.

Because the control group was not given a placebo, it’s possible that the reduction in negative affect in the 85% dark chocolate group could be from a placebo effect.

It’s also worth addressing the lack of apparent effect in the 70% dark chocolate group. It might be expected that 70% would have an intermediary effect on negative affect (more than the control but less than the other chocolate), but given the sample sample sizes of the groups, it's possible that this study was underpowered to detect a significant effect.