Mental Health and the Gut Biome

Research status: Strong

In the past two decades, hundreds of studies have been conducted on probiotics and mental health.

Many cultures and languages intuitively refer to the physiological interaction between the gut and the brain in phrases such as “gut feeling” or “bauchgefühl.”

Scientists have been encouraged to explore the “gut-brain axis” by the anatomical fact that the brain has more connections with the digestive system - the stomach, small intestine, and large intestine - than any other part of the body.

But despite the strong linkage, people were unsure about directionality - whether mental health was causing gut imbalance symptoms, or whether gut imbalances could generate psychiatric disorders.

However, several studies - including randomized controlled trials (RCTs) - have demonstrated that probiotics can reduce psychiatric disorders.

In the studies below, researchers found that probiotics can be a promising supporting tool in addressing major depressive disorder (MDD), bipolar disorder, and postpartum depression.

Selected scientific literature:

1. [Review] Probiotics for the treatment of depressive symptoms: An anti-inflammatory mechanism?
  • “Emerging evidence suggests that modifying the composition of the gut microbiota via probiotic supplementation may be a viable adjuvant treatment option for individuals with major depressive disorder (MDD). Convergent evidence indicates that persistent low-grade inflammatory activation is associated with the diagnosis of MDD as well as the severity of depressive symptoms and probability of treatment response. The available evidence suggests that probiotics should be considered a promising adjuvant treatment to reduce the inflammatory activation commonly found in MDD.“
2. [Review] Moody microbiome: Challenges and chances.
  • This review of clinical trials indicates a positive effect of probiotic use in major depressive disorder (MDD), bipolar disorder, psychological distress and decreased depression and anxiety scores.
3. [Human] Effect of probiotic and prebiotic vs placebo on psychological outcomes in patients with major depressive disorder: A randomized clinical trial
  • One hundred and ten depressed patients were randomly assigned to receive the probiotic (Lactobacillus helveticus and Bifidobacterium longum), prebiotic (galactooligosaccharide) or placebo for 8 weeks. From baseline to 8 weeks, probiotic supplementation resulted in a significant decrease in BDI (Beck’s Depression Inventory) score compared to the placebo.
4. [Human] A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood
  • “Heightened cognitive reactivity to normal, transient changes in sad mood is an established marker of vulnerability to depression and is considered an important target for interventions. The present study aimed to test if a multispecies probiotic containing Bifidobacterium bifidum W23, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus brevis W63, Lactobacillus casei W56, Lactobacillus salivarius W24, and Lactococcus lactis (W19 and W58) may reduce cognitive reactivity in non-depressed individuals. Compared to participants who received the placebo intervention, participants who received the 4-week multispecies probiotics intervention showed a significantly reduced overall cognitive reactivity to sad mood, which was largely accounted for by reduced rumination and aggressive thoughts.
5. [Human] Effect of Lactobacillus rhamnosus HN001 in Pregnancy on Postpartum Symptoms of Depression and Anxiety: A Randomised Double-blind Placebo-controlled Trial
  • “The aim of this study was to evaluate the effect of Lactobacillus rhamnosus HN001 (HN001) given in pregnancy and postpartum on symptoms of maternal depression and anxiety in the postpartum period. 212 women were randomised to HN001 and 211 to placebo. 380 women (89.8%) completed the questionnaire on psychological outcomes, 193 (91.0%) in the treatment group and 187 (88.6%) in the placebo group. Mothers in the probiotic treatment group reported significantly lower depression scores (HN001 mean = 7·7 (SD = 5·4), placebo 9·0 (6·0); effect size -1·2, (95% CI -2·3, -0·1), p = 0·037) and anxiety scores (HN001 12·0 (4·0), placebo 13·0 (4·0); effect size -1·0 (-1·9, -0·2), p = 0·014) than those in the placebo group. Rates of clinically relevant anxiety on screening (score > 15) were significantly lower in the HN001 treated mothers (OR = 0·44 (0·26, 0·73), p = 0·002).”