Research Update: Consumption of 85% Cocoa Dark Chocolate Improves Mood in Association With Gut Microbial Changes in Healthy Adults: A Randomized Controlled Trial

Research Update articles are produced in order to keep practitioners up to date on impactful research that is relevant to the field of integrative medicine. These articles may contain summaries of recent studies, events, or other industry news that advances current knowledge and standards of care.

The following article summarizes the research conducted by Shin et al. titled Consumption of 85% cocoa dark chocolate improves mood in association with gut microbial changes in healthy adults: a randomized controlled trial, which was published in the Journal of Nutritional Biochemistry in 2022. (18)

Overview

Background

Dark chocolate has long been recognized for its ability to improve mood. (10) However, research on the impact of cocoa products on mood is inconsistent. Some studies show that it ameliorates negative emotions, (10)(11)(16)(20) while others report no significant effect. (9) Some studies show that the amount of cocoa consumed may alter the effect on mood as higher doses of cocoa positively impact mood compared to lower doses. (2)(15) Most studies also typically investigate the acute effects of dark chocolate following experimentally induced psychological stress, as opposed to dark chocolate’s emotional effects on everyday life.  

The underlying mechanism behind the mood-altering effects of dark chocolate has not been clearly determined. Evidence suggests that it may originate from the variety of polyphenolic compounds in dark chocolate, (7)(17) which have antioxidant, (3) anti-inflammatory, (19) and cortisol-lowering effects. (7) Polyphenol compounds in cocoa such as catechin and epicatechin can cross the blood-brain barrier, (14) and animal studies suggest that the polyphenolic extracts of cocoa may have anti-depressive effects. (19) But this may only be one piece of the puzzle. 

Evidence also suggests that the gut microbiota plays a major role in the regulation of mood via the gut-brain axis. (1)(5)(6)(8)(12) In fact, one animal study demonstrated that mice that received gut microbiota transplants from patients with major depressive disorder (MDD) exhibited depressive behavior, whereas those that received microbiota from individuals without MDD did not. (21) Given the relationship between gut microbiota and mood, the present study examined the impact of dark chocolate consumption on mood in healthy adults and whether changes in mood were associated with alterations in the gut microbiota.

Method

Forty-eight healthy adults (20 to 30 years old) were recruited at Seoul National University. Prior to enrollment, researchers ensured that participants did not regularly consume sweets such as chocolate or cake more than twice a day, did not have a history of gastrointestinal disease or diabetes, had not taken antibiotics or pre/probiotics within the last three to six months respectively, and were not classified to have borderline clinical depression as per the Korean version of the Beck Depression Inventory. 

Participants were randomized to either consume 30 g per day of 85% cocoa chocolate (DC85), 70% cocoa chocolate (DC70), or no chocolate as a control for three weeks. This equated to approximately 400 mg of polyphenols per day in the DC85 group and 250 mg of polyphenols in the DC70 group. The investigators were not blinded to this allocation, but participants in the DC85 and DC70 groups were blinded as to whether they received high-cocoa or low-cocoa chocolate.

Participants received one week’s worth of chocolate (Weinrich 1895 Fine Dark Chocolate) at a time and were instructed to eat 10 g of chocolate, three times per day, at the same times each day (7:00 to 9:00, 12:00 to 14:00, 17:00 to 19:00) for three weeks. Compliance was calculated based on the number of chocolate pieces returned each week.

Several parameters were assessed before and after the experiment including body composition, dietary intake, gut microbiota, and mood. Mood was assessed using the Korean version of the Positive and Negative Affect Schedule (PANAS). Dietary intake was assessed using the 3-day food record (3DR) method, which had participants report the food they consumed previously on three random days (two weekdays and one weekend day). The total amount of calories, carbohydrates, proteins, and fats were determined using the Computer Aided Nutritional Analysis Program. Participants in the control group were also asked to record the snacks that they ate every day during the experimental period. For gut microbiome analysis, participants in the DC85 and control groups were asked to bring fecal samples to the lab, where fecal 16S rRNA sequencing analysis was performed to identify changes in the diversity and composition of the gut microbiota. 

Results

With respect to baseline parameters, there were no significant differences in sex ratio, age, weight, body mass index (BMI), skeletal muscle mass, and body fat mass across the three groups. Additionally, there were no significant differences between caloric and macronutrient intake across the groups. All participants completed the three-week intervention with similar compliance rates between the DC85 and DC70 groups. Anthropometric parameters and usual dietary intake were maintained during the trial.

In terms of the impact on mood, the DC85 group had a significant decrease in negative affect that was approximately 2.6 times greater than the control group. On the other hand, there were no significant changes observed in the DC70 group compared to controls. Dark chocolate consumption had no significant impact on positive affect.

Analysis of the gut microbiota found that there was significantly higher microbial diversity in the DC85 group than the control group. Additionally, the abundance of Blautia obeum and Faecalibacterium prausnitzii species were significantly different in the DC85 group compared to the control group. In the DC85 group, Blautia obeum levels were significantly elevated, while Faecalibacterium prausnitzii levels were reduced. The increased abundance of Blautia obeum was significantly associated with positive changes in mood scores, but Faecalibacterium prausnitzii levels were not significantly correlated with mood status.

The changes in the gut microbiota demonstrate that dark chocolate has prebiotic effects. The authors suggest that increased production of butyrate, a short chain fatty acid, by the microbial species Blautia obeum (17) may contribute to the positive changes in mood observed in the DC85 group. Butyrate is a recognized modulator of brain function and has demonstrated antidepressant-like effects in animal studies. (7) 

Critical analysis 

This randomized controlled trial (RCT) had many strengths. The design had a vigorous exclusion criteria for recruitment, which eliminated the potential for many confounding factors such as the alteration of the participants’ gut microbiota by antibiotics or probiotics. The study was also well-controlled as there were no significant differences between the groups with respect to sex ratio, anthropological measures, and usual dietary intake. Furthermore, the methodological design of this study actually allowed for the direct comparison of the efficacy of dosing. Another strength of the study was the use of the PANAS to assess mood, as its reliability and validity have been well-demonstrated. (4,13) 

The study also had several limitations. One limitation was that the gut microbiota of participants in the DC70 group was not analyzed. This analysis could have given additional insight into the prebiotic effects of dark chocolate. Since this was not measured, it is possible that the difference between the two groups was not due to the dose of cocoa but rather to differences in gut microbiome between the groups. Perhaps if the gut microbiome between the groups was the same, similar benefits might have been observed. 

Another limitation involves how the dietary assessment was conducted. Since the 3DR only accounts for the dietary intake over three days, it may not be representative of the true dietary intake of participants. Additionally, the dietary analysis did not take into account micronutrient intake, which also may influence mood. 

Other factors that could also influence mood were not assessed such as differences in physical activity, engagement in mindfulness practices, and other supplements that can influence mood. 

Another limitation of the study was that the control group lacked an appropriate placebo, which should be considered in future research. The reporting of blinding was also unclear, which makes it difficult to know how well-controlled the study truly was. 

The bottom line

This study demonstrated that daily intake of dark chocolate with a higher cocoa content (85%) had a positive influence on mood by reducing negative affect. In addition to the potential anti-inflammatory, antioxidant and cortisol-lowering benefits of the polyphenols in dark chocolate, cocoa may also impact mood through prebiotic effects by altering the diversity and composition of the gut microbiome. The decreased negative affect scores observed in this study were associated with increased gut microbial diversity and an abundance in Blautia obeum, which may have, in turn, improved mood through the gut-brain axis.