Probiotics vs. Depression: Can They Help?

randomized-controlled-trial PMID: 29731182

Quick Summary: A study found that taking probiotics (good bacteria) helped reduce symptoms of depression in people with major depressive disorder (MDD). Prebiotics (food for good bacteria) didn't show the same benefit.

Probiotics and Depression: What the Research Says

This research looked at whether probiotics and prebiotics could help people with depression. The study found that taking a specific probiotic supplement for 8 weeks helped reduce depression symptoms. People taking the probiotic felt better, according to a standard depression test. However, the prebiotic didn't have the same effect.

Study Details

Who was studied: 81 adults with major depressive disorder (MDD).

How long: 8 weeks.

What they took:

Probiotic group: A daily capsule with Lactobacillus helveticus and Bifidobacterium longum (specific types of good bacteria).
Prebiotic group: A daily powder with galactooligosaccharide (GOS), a type of prebiotic (food for good bacteria).
Placebo group: A daily inactive pill (like a sugar pill).

What This Means For You

Probiotics might help: If you have depression, talking to your doctor about taking a probiotic containing Lactobacillus helveticus and Bifidobacterium longum could be a helpful addition to your treatment plan.

Prebiotics alone may not be enough: This study didn't find that prebiotics alone helped with depression.

Talk to your doctor: Always discuss any supplements with your doctor before starting them, especially if you're already taking medication for depression.

Study Limitations

Small study: The study only included a limited number of people, so more research is needed.

Short time frame: The study lasted only 8 weeks. We don't know if the benefits would last longer.

Specific strains matter: The study used specific types of probiotics. Other probiotics or prebiotics might not have the same effect.

More research needed: This is just one study. More research is needed to confirm these findings and understand how probiotics work to help with depression.

Key Findings

This 8-week randomized clinical trial found that probiotic supplementation (containing Lactobacillus helveticus and Bifidobacterium longum) significantly reduced Beck Depression Inventory (BDI) scores in patients with major depressive disorder (MDD) compared to placebo (17.39 → 9.1, p = 0.042). Prebiotic supplementation (galactooligosaccharide) did not show statistically significant improvements in depression symptoms (19.72 → 14.14, p > 0.05). Secondary outcomes revealed that probiotics modestly altered tryptophan metabolism, with a significant decrease in the kynurenine/tryptophan ratio (adjusted for serum isoleucine, p = 0.048) and an increase in the tryptophan/isoleucine ratio (p = 0.023) compared to placebo.

Study Design

The study was a double-blind, placebo-controlled randomized clinical trial involving 110 adults (mean age 36.5 ± 8.03 years) diagnosed with MDD. Participants were assigned to one of three groups: probiotic, prebiotic, or placebo. The trial lasted 8 weeks, with 81 completers (28 probiotic, 27 prebiotic, 26 placebo). Serum biomarkers (tryptophan, kynurenine, branched-chain amino acids) were measured via HPLC and ELISA, while dietary intake and physical activity were recorded at baseline.

Dosage & Administration

Probiotic: Capsules containing L. helveticus R0052 and B. longum R0175, each at 1 × 10⁹ CFU/day.
Prebiotic: 4.5 g/day of galactooligosaccharide (GOS) in powder form.
Placebo: Starch powder (prebiotic placebo) and maltodextrin capsules (probiotic placebo).
All interventions were administered once daily.

Results & Efficacy

Primary Outcome: Probiotic supplementation reduced BDI scores by 8.29 points (95% CI: 1.76–2.93), significantly more than placebo (2.63-point reduction, p = 0.042) and prebiotic (5.58-point reduction, p = 0.042).
Secondary Outcomes:
Kynurenine/tryptophan ratio decreased in the probiotic group compared to placebo after adjusting for isoleucine (p = 0.048).
Tryptophan/isoleucine ratio increased significantly in the probiotic group (p = 0.023).
No significant differences were observed in the prebiotic group for any biomarkers.

Limitations

Small Sample Size: Only 81 completers may limit statistical power.
Short Duration: 8 weeks may be insufficient to observe long-term effects.
Incomplete Mechanistic Data: Gut microbiota composition was not directly measured, so changes in microbial populations could not be linked to outcomes.
Placebo Design: The prebiotic placebo (starch powder) may not fully mimic the inert effects of GOS.
Dietary Confounding: Physical activity and diet were recorded only at baseline, not monitored throughout the trial.
Single Prebiotic Strain: Results may not generalize to other prebiotics or synbiotic combinations.

Clinical Relevance

For individuals with MDD, this study suggests that probiotics containing L. helveticus and B. longum may improve depressive symptoms, as measured by the BDI. However, prebiotic supplementation alone (4.5 g GOS/day) did not demonstrate significant benefits. The findings support further investigation into probiotics as adjunctive therapies for depression but highlight the need for larger trials to confirm efficacy and explore mechanisms. Supplement users should note that strain-specific probiotics, not all probiotics or prebiotics, may yield these effects, and individual responses could vary.