🧠 Microbiome and Mental Health (Psychobiotics): RCTs of Lactobacillus and Bifidobacterium
How gut bacteria affect mood and anxiety
Psychobiotics are probiotics (live bacteria) that, when consumed in sufficient amounts, may affect mental health through the gut-brain axis. Research shows that strains of Lactobacillus and Bifidobacterium may affect mood, anxiety and stress.
What are psychobiotics
The term "psychobiotic" was coined in 2013. It refers to live microorganisms that, when consumed in sufficient amounts, benefit mental health. In studies, strains of Lactobacillus and Bifidobacterium are most often studied.
- Live bacteria that affect the mind.
- Most often Lactobacillus and Bifidobacterium.
- Act through the gut-brain axis.
- Affect stress, anxiety and mood.
Gut-brain axis
The gut-brain axis is the two-way connection between the GI tract and the brain via the vagus nerve, the immune system and neurotransmitters. Microbiota can influence the brain, and stress can change the microbiota composition.
| Pathway | Mechanism |
|---|---|
| Vagus nerve | Direct gut-brain connection |
| Serotonin | Synthesis in gut, affects mood |
| Immunity | Cytokines affect the brain |
| Metabolites | SCFA and microbial neurotransmitters |
RCTs of Lactobacillus
Studies of Lactobacillus strains (e.g. L. rhamnosus, L. plantarum, L. helveticus) have shown a potential effect on reducing anxiety and stress. Some RCTs report a reduction in cortisol levels.
- L. rhamnosus is studied in the context of stress.
- L. helveticus is in combinations for anxiety.
- Some RCTs show reduced cortisol.
- The data are promising but need confirmation.
RCTs of Bifidobacterium
Strains of Bifidobacterium (e.g. B. longum, B. bifidum) are also studied. Some research shows a positive effect on mood, and the gut-brain link is recognised as an important direction.
- B. longum is studied in psychobiotic combinations.
- Possible effect on mood and anxiety.
- Effects depend on the strain and dose.
- Larger confirmatory studies are needed.
Food: sources
Probiotics and the food that feeds them (prebiotics) are found in fermented foods and fibre. Both matter for microbiome health.
| Food | Content | Comment |
|---|---|---|
| Yoghurt | Live lactobacilli | Portion 150–200 g |
| Kefir | Lacto- and bifidobacteria | Glass 200 ml |
| Sauerkraut | Lactic acid bacteria | Portion 100 g |
| Kimchi | Fermented bacteria | Traditional Korean |
| Oats/legumes | Fibre (prebiotic) | Feeds microbiota |
How much to eat
- Fermented foods: a portion of yoghurt or kefir daily.
- Fibre: 25–30 g a day (vegetables, legumes, whole grains).
- Variety: different fermented foods = bacterial diversity.
Norms and dosages
| Indicator | Value | Comment |
|---|---|---|
| Probiotic dose | 1–10 billion CFU | Usually per capsule |
| Duration | 4–12 weeks | In studies |
| Frequency | 1–2 times a day | Per label |
| Fibre | 25–30 g/day | Feeds microbiota |
Practice and limitations
- Choose strains with proven efficacy in RCTs.
- Check CFU count and production date.
- Combine probiotics with prebiotics (fibre).
- Probiotics are a supplement, not a replacement for therapy.
- For serious conditions, consult a doctor.
What are psychobiotics?
Probiotics that, when consumed sufficiently, affect mental health through the gut-brain axis.
How do bacteria affect the brain?
Through the vagus nerve, serotonin synthesis, the immune system and metabolites.
Which strains are studied?
Most often Lactobacillus (L. rhamnosus, L. helveticus) and Bifidobacterium (B. longum).
Do psychobiotics help with anxiety?
Some RCTs show a reduction in anxiety and stress, but the data need confirmation.
Where is serotonin found?
About 90% of serotonin is produced in the gut, linking the microbiome and mood.
Which foods have probiotics?
Yoghurt, kefir, sauerkraut, kimchi and other fermented foods.
How much probiotic to take?
Usually 1–10 billion CFU a day, for 4–12 weeks, per the label.
Is fibre needed for the microbiome?
Yes, fibre (25–30 g/day) feeds beneficial bacteria and boosts probiotics.
Can probiotics replace treatment?
No, psychobiotics are an auxiliary direction, not a replacement for depression or anxiety therapy.
Which axis connects gut and brain?
The gut-brain axis — via the vagus nerve, immunity and neurotransmitters.