Bipolar Disorder

What Gut Bacteria Have to Do With Mood Swings

A randomised controlled trial has tested this connection, which puts it on firmer ground than most gut and mental health topics. Bipolar disorder involves episodes of mania or elevated mood alternating with periods of depression. The gut enters the picture through inflammation, which is raised in many people with the condition and has been linked to relapse. Bacteria influence how much inflammatory signalling reaches the rest of the body. That is the thread the research has followed.

A bacterium that goes missing

Researchers compared stool samples from 115 people with bipolar disorder against 64 without it.

One finding stood out. Faecalibacterium was reduced in the bipolar group. Faecalibacterium is one of the main producers of butyrate. Butyrate is a compound made by fermenting fibre. The cells lining the gut use it as fuel, and it helps restrain inflammation.

The detail that makes this more than a list is what the amount tracked with. Among people with bipolar disorder, those with more Faecalibacterium reported a lower burden from their condition across several measures, including sleep.

So the bacterium was not simply present or absent by diagnosis. Its abundance varied with how people were actually doing.

That is still a snapshot. Reduced Faecalibacterium appears in several conditions involving inflammation, so it is not specific to this one.

Source: Gut microbial clues to bipolar disorder: State-of-the-art review of current findings and future directions

The trial that tested it properly

An association like that invites an experiment, and one was run.

Sixty-six people who had recently been discharged from hospital after an episode of mania were randomly assigned to receive either a probiotic or a placebo alongside their usual treatment. The probiotic contained Lactobacillus rhamnosus GG and Bifidobacterium animalis subspecies lactis Bb12. It ran for 24 weeks.

The probiotic group were readmitted to hospital less often over that period. When they were admitted, they spent fewer days there.

The effect was strongest in participants who had high levels of inflammation in their blood at the start, which fits the reasoning behind the trial rather than appearing out of nowhere.

This was an addition to standard psychiatric treatment, not a replacement for it. Everyone in both groups continued their prescribed medication throughout.

A probiotic taken this way still depends on being fed. Introducing bacteria without supplying the fibre and plant compounds they live on is like restocking a lake and never adding food. The population thins out, and whatever it was producing stops.

Source: Adjunctive probiotic microorganisms to prevent rehospitalization in patients with acute mania: A randomized controlled trial

How far the evidence currently reaches

One trial is a starting point rather than a conclusion, so it is worth setting alongside the wider picture.

Reviews pooling the observational studies agree on one thing. Overall bacterial richness tends to be reduced in bipolar disorder, which fits the finding about Faecalibacterium above.

What the trials have measured so far differs. The 66-person study counted hospital admissions and found fewer. A smaller study of 38 people rated day-to-day symptom severity instead and found no change, so the benefit demonstrated to date is about relapse serious enough for hospital rather than about everyday mood.

That is a narrow claim, and it is the one the evidence currently supports.

Source: Role of the gut microbiome in three major psychiatric disorders

What this means for you

Bipolar disorder needs specialist psychiatric care and prescribed medication, and changing that medication without medical advice risks relapse. In addition, the trial above found a probiotic added to standard treatment reduced hospital readmission over six months, which is worth raising with a psychiatrist. A varied, plant-rich diet supports Faecalibacterium and the wider community around it. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.