Prebiotics to improve mood in people with obesity Original paper

The gut microbiome, operating through the gut-brain axis, may possibly contribute to psychological disorders.^[1] Additionally, research suggests that people with obesity have an altered gut microbiome.^[2] Can reshaping the gut microbiome with prebiotics improve psychological health in people with obesity and do the baseline characteristics of the gut microbiome determine the response to the intervention?

This 3-month randomized controlled trial enrolled 106 participants with obesity and at least one obesity-related metabolic disorder (i.e., dyslipidemia, prediabetes/diabetes, hypertension, fatty liver disease). Participants were randomized to receive either 16 grams/day of a prebiotic (inulin) or a placebo. The participants were also prescribed a hypocaloric diet (-30% of their calculated energy expenditure).

The primary outcome was changes in gut microbiota composition. The secondary outcomes were various physiological parameters (e.g., body composition, blood markers, insulin resistance) and psychological measures (e.g., mood, emotional regulation, and cognitive assessments). All endpoints were assessed at baseline and at 3 months.

Gut bacteria levels, markers of inflammation, and severity of insulin resistance at baseline predicted the effect of prebiotics on the participants’ psychological measures. Positive responders to the prebiotic had higher baseline levels of Coprococcus bacteria, IL-8 (a marker of inflammation), and higher HOMA-IR scores (an indicator of greater insulin resistance). The participants in the high Coprococcus group showed improvements in emotional competence and mood after taking prebiotics, but their cognitive scores were unchanged.

Emotional competency (the ability to identify, interpret and respond to emotions in others and yourself) tended to increase in the prebiotic group and tended to decrease in the placebo group but the difference was nonsignificant. Scores for negative emotions decreased and cognitive flexibility increased only in the prebiotic group.

A positive response to the prebiotic was seen in those with the highest levels of insulin resistance and Coprococcus at baseline. Postintervention, the positive responders had increased Bifidobacterium and Haemophilus bacteria, increased IL-8, decreased DPP-IV (an enzyme associated with immune regulation), and decreased subcutaneous fat compared to the nonresponders. Overall, prebiotic supplementation improved mood, cognitive flexibility, and fat mass.

The increase in IL-8 among the positive responders was a surprising outcome. The researchers note that studies have linked weight loss in obese people to an increase in inflammatory cytokines, possibly due to compounds released from fat tissue.^[3][4] Also, it can’t be ruled out that the reduced-calorie diet played a role in improving several outcomes in those with the worst metabolic profiles, which is the group that was shown to benefit from the prebiotic.