Depression affects over 270 million people worldwide.
New research is investigating whether manipulating gut bacteria with probiotics, prebiotics or synbiotics can help treat depression symptoms.
Key Facts:
- Probiotics are live microorganisms that provide health benefits when consumed. Prebiotics are food for probiotics. Synbiotics contain both probiotics and prebiotics.
- A meta-analysis combined results from 13 studies with 786 participants. Overall, probiotics, prebiotics and synbiotics improved depression symptoms more than placebo.
- The improvements were significant for mild to moderate depression. Probiotics showed the strongest effects. More research is needed on prebiotics and synbiotics.
- Participants with less than 70% females showed greater improvement. Biological sex impacts gut bacteria and the immune response.
- Potential mechanisms relate to changes in gut bacteria, reduced inflammation, and effects on brain signaling chemicals.
Source: BMC Psychiatry 2023
The Gut-Brain Axis & Depression
The gut contains trillions of bacteria, viruses and fungi collectively called the gut microbiome.
There is growing evidence of a two-way communication system between the gut and brain called the gut-brain axis.
The gut microbiome interacts with the brain indirectly through pathways like the vagus nerve, immune system, and bloodstream chemicals.
Research shows differences in gut bacteria between people with and without depression. Stress can disrupt healthy gut bacteria.
Antibiotics and poor diet also negatively impact the gut microbiome.
On the other hand, probiotics, prebiotics and synbiotics may help restore a healthy balance.
Clinical trials are examining their effects on depression.
What are Probiotics, Prebiotics and Synbiotics?
Probiotics are live microorganisms that provide a health benefit when consumed in adequate amounts.
Common probiotic strains are from the Lactobacillus and Bifidobacterium groups of bacteria.
They are similar to the beneficial bacteria normally found in a healthy human gut.
Probiotics can be consumed as capsules, powders or fermented foods like yogurt, kefir and sauerkraut.
Prebiotics are specialized plant fibers that probiotic bacteria feed on.
They act as “fertilizer” to help probiotics multiply and thrive.
Prebiotic fiber is found in foods like garlic, onion, asparagus, oats and bananas.
Synbiotics contain both probiotics and prebiotics.
The goal is for the prebiotics to boost the growth and function of the probiotics.
Potential Mechanisms of Action
There are several ways probiotics, prebiotics and synbiotics could help treat depression:
Modulating Gut Bacteria: Probiotics help restore a healthy balance of gut bacteria. Animal studies show differences in gut bacteria between those responding/not responding to probiotics. Fecal transplants from healthy donors also improve depression symptoms in animals.
Reducing Inflammation: People with depression tend to have higher levels of inflammatory markers like C-reactive protein and cytokines. Probiotics and prebiotics have anti-inflammatory effects in some studies. However, different strains have different effects.
Influencing Brain Signaling: Beneficial gut bacteria may positively affect key signaling chemicals in the brain like serotonin, dopamine and BDNF (brain-derived neurotrophic factor). They can also dampen stress system over-activity.
Meta-analysis of trials using probiotics for depression
The recent meta-analysis combined results from 13 randomized controlled trials on probiotics, prebiotics or synbiotics for depression.
It included 786 participants with a clinical diagnosis of depression but no other major health issues.
About 75% of participants were female. The average age ranged from 34 to 53 years old across studies. Interventions lasted from 3-24 weeks.
Nine studies used probiotics, one used prebiotics, two compared probiotics and prebiotics, and one used synbiotics.
Probiotics included single strains like Lactobacillus casei or combinations like Lactobacillus acidophilus and Bifidobacterium bifidum.
The prebiotics were galacto-oligosaccharides and fructo-oligosaccharides. Most interventions were taken alongside antidepressant medication.
Do Probiotics, Prebiotics or Synbiotics Help Treat Depression?
The meta-analysis found that overall, probiotics, prebiotics and synbiotics improved depression symptoms significantly more than placebo.
Ten studies used the Hamilton Depression Rating Scale.
This showed a large improvement over placebo.
Five studies used the Beck Depression Inventory, also showing significant benefit over placebo.
The positive effects were seen in people with both mild to moderate depression.
However, subgroup analysis showed that only agents containing probiotics (probiotics and synbiotics) were significantly better than placebo.
The few studies using only prebiotics did not show a significant difference from placebo.
Looking at probiotics, benefits were seen whether single strains or multiple strains were used.
The length of treatment did not impact efficacy. Improvements remained when participants were evaluated again weeks after stopping treatment.
Studies with a lower percentage of females (<70%) showed more pronounced improvements than studies with mostly females.
This suggests that biological sex may play a role in responses.
Assessing changes in gut bacteria, the meta-analysis found no major differences in overall diversity after treatment.
But specific taxa like Bifidobacterium increased, which is thought to be beneficial.
Due to limited data, no conclusions could be made about effects on inflammatory markers.
In summary, probiotics show promise for mild to moderate depression, especially as an add-on treatment.
More research is needed on optimal strains, dosages and mechanisms.
Prebiotics and synbiotics require further high-quality studies to confirm their antidepressant effects.
Practical Considerations for Using Probiotics
Probiotics are generally considered safe, but some points for consumers to consider:
- Consult your doctor before starting, especially if you have a compromised immune system.
- Start with the recommended dosage on the label and gradually increase if needed.
- Take at least 1-2 hours apart from antibiotics, which can kill probiotics.
- Look for reputable brands that list strain names, CFU counts and expiration dates.
- Probiotic supplements require refrigeration to maintain potency.
- Prebiotics may initially cause more gas and bloating until your body adjusts.
- Combine probiotics with prebiotic fiber sources to help the good bugs flourish.
Final takeaways: probiotics & depression
Research on probiotics, prebiotics and synbiotics for depression is an exciting new frontier.
Early clinical trials show promising results, especially for probiotics in mild to moderate depression.
However, larger and longer studies are needed to confirm benefits.
These treatments appear relatively safe and may help restore a healthy gut microbiome.
But effects can vary greatly depending on the strains and dosages used.
They should not replace standard antidepressant therapy without consulting your doctor.
Modifying gut bacteria through food, stress reduction and other lifestyle approaches also support a healthy microbiome.
An integrated approach combining diet, microbial therapies, psychotherapy and medication may ultimately provide the greatest benefits.
References
- Study: Effect of prebiotics, probiotics, synbiotics on depression
- Authors: Qin Zhang et al. (2023)
