A gut feeling: exploring the world of ‘psychobiotics’

Could anxiety be connected to your digestive system?

We’re used to hearing how looking after the friendly bacteria in your gut can improve digestion and boost the immune system. But could it also lift your mood or even sharpen your brain if you have dementia?

A few years ago this would be dismissed as quackery, but new research suggests there is a clear link between the trillions of microbes in the gut and a healthy brain.

An illustration to highlight psychobiotics in the gutCredit: Andrew Baker

Professor Philip Burnet, in the Department of Psychiatry at Oxford University, is one of a growing number of doctors and scientists excited by the idea of ‘psychobiotics’ – either taking probiotics (live bacteria) or prebiotics (food to nourish those bacteria), in an attempt to alter mood.

In a recent randomised, double-blind, placebo-controlled trial, not yet published, he and his team found that a daily dose of the live probiotic supplement Bio-Kult Advanced significantly lifted the spirits of 35 people suffering low mood, compared with 35 others who took a daily dummy pill for four weeks.

‘We chose people with milder symptoms who weren’t taking antidepressants, rather than people with clinical depression who were on medication because we wanted to see if probiotics really could improve their mood,’ explains Professor Burnet.

A benefit to the brain?

‘Both the participants taking the probiotic supplement and those in the placebo group improved but those taking the probiotics improved by an additional 20%.’ Those taking the supplement also had lower saliva levels of the stress hormone cortisol, suggesting an easing of their stress levels.

Professor Burnet is seeking funding for a larger trial that he hopes will confirm the results, but it adds to the large number of studies suggesting that manipulating the gut microbiome with either probiotics or their cousins, prebiotics, may be of benefit to the brain.

Some doctors see psychobiotics as a useful tool for people with mild depressive symptoms who prefer not to take medication, or as an add-on to antidepressants in those with clinical depression.

The best foods to boost gut bacteria

Wholewheat bread, brown rice, barley

Beans, tofu, chickpeas, nuts

Yogurt, kefir, buttermilk, aged cheese

Leeks, asparagus, onions, wheat, garlic, chicory, oats, soya beans, Jerusalem artichokes

But how do they work? After all, the gut is a long way from the brain. In fact, there’s a brain-gut axis, a kind of two-way chemical ‘superhighway’ that connects the two, explains Dr Gerard Clarke of APC Microbiome Ireland at University College Cork.

One possibility is that the gut produces nerve messenger chemicals that influence mood – in fact it makes almost 95% of the body’s serotonin, a key mood regulator. These chemicals are thought to communicate directly with the brain via the vagus nerve, which connects the brain and other organs.

Another possibility is via the hormonal system, as gut bacteria may activate hormone-producing cells in the gut. One, galanin, is involved in how the brain perceives pain, the sleep/wake system and mood regulation.

Other researchers at APC are examining the role of gut bacteria in healthy ageing as part of the Irish Eldermet project in people over 65.

‘The composition of microbes in the gut is more chaotic in later life,’ says Clarke. ‘As we age, our brain function declines and physiologically, we are in a state of low-grade inflammation, called inflammaging. We want to know the consequences of this and whether we may be able to target the alterations in specific microbes to improve aspects of immune or brain health.’

Remain cautious

An overview of studies published in the journal Aging suggested that probiotics may improve cognitive performance in people with Alzheimer’s or its forerunner, mild cognitive impairment. But there’s no clear take-home message yet.

Some experts urge caution. ‘We’re still lacking large-scale, robust, randomised, controlled trials in humans,’ says Dr Sanjay Noonan, co-author of a 2020 review examining the usefulness of pre- and probiotics for treating anxiety and depression.

So, if we do want to try a pyschobiotic, which is best? One of those little milky probiotic drinks or a capsule? Some research suggests the beneficial bacteria in the drinks can be killed off by stomach acid.

‘Many of the strains commonly used as probiotics can survive gastric acidity, but the degree of survival is strain-specific,’ says Dr Clarke. ‘The advantage of capsules is that they can help strains that don’t survive well to bypass the impact of stomach acid.’

Scientists haven’t been able to pin down the exact strains that may improve mental health, but look out for a product that is backed by evidence, and eat a bacteria-friendly diet.

Jo Mauden, 51, from Hertfordshire, tried a capsule supplement after becoming low during the pandemic lockdowns. ‘In just a few weeks I was coping a lot better, my concentration and even my memory had dramatically improved. I was able to absorb information better and I no longer felt overwhelmed. I would say that probiotics have had a tremendous impact on my life.’

Written by Patsy Westcott