Food to boost your mood: Gut bacteria directly linked to your mental health

Two professors at UCC have revealed links between gut bacteria and mental health, writes Ellie O’Byrne

Ted Dinan, Professor of Psychiatry at University College Cork and Professor John Cryan, Chair of the Department of Anatomy and Neuroscience at University College Cork. Picture: Clare Keogh

We are outnumbered. For every human cell in your body, there are ten cells of non-human origin. These interlopers make up our microbiome: the community of extraordinary little organisms in the form of bacteria, yeasts and viruses that makes up between 1% and 3% of our body weight… and may be influencing our behaviour and moods far more than we realise.

Our microbes communicate directly with our brain and play a key role in tackling depression, stress, anxiety and other mental health complaints, according to The Psychobiotic Revolution, a new book co-authored by two UCC professors.

Findings from clinical research conducted in UCC by Professors John Cryan and Ted Dinan, show how microbes use the nerve network surrounding our gut, which is so complex that it has been christened the “second brain”, to get their message across to our brain. Gut inflammation has a such a strong link to depression, they say, that we ignore it at our peril: if their book is to believed, we can, quite literally, eat ourselves happy.

According to The Psychobiotic Revolution, “good” bacteria can secrete neurotransmitters so powerful that they rival the effects of Prozac, while “bad” bacteria can make substances that increase anxiety and depression, and may even impact on symptoms associated with autism, like anti-social and repetitive behaviours.

They coined the term “psychobiotics” to refer to microbes with a positive impact on mental health. The book has been widely heralded as important within the scientific community and The Lancet, the world’s leading medical journal, recently gave it a positive review.

Yet John Cryan, a professor of Anatomy and Neuroscience at UCC, is aware that some of the implications of his team’s work could be controversial, most notably in the area of autism.

Rates of gastro-intestinal disease like irritable bowel syndrome and Crohn’s disease are high in people with autism spectrum disorder, and Prof Cryan, alongside his colleague, consultant psychiatrist, Prof Ted Dinan, is exploring the role of microbes in this phenomenon.

“We ended up in autism research largely because it’s where the data brought us,” Cryan says. “In our experimental models in animals, we found that these effects were very prevalent, especially in males over females. We started researching to see if this has any relevance to autism. We think it does, but we’re still in the early days of finding out what that is.

“There’s a large group of people who really believe in the concept of neurodiversity, and I think that’s brilliant. But it doesn’t mean we can’t look at ways to alleviate symptoms in both kids and adults. We want to avoid misunderstandings, and make sure that people know the goal is to make people’s lives better, in whatever way we can.”

Autism aside, Cryan hopes the message of their book is picked up on by a wide readership, both amongst sufferers of mental health conditions and amongst the medical community: the psychobiotic revolution of the book’s title.

“It’s a topic that’s beginning to grab people’s imaginations,” he says. “A revolution has to begin somewhere, and this has been a particularly slow-burning revolution, but we feel it’s a game-changer.

“How many GPs are giving out nutritional advice or asking questions about diet before they prescribe? We’re not suggesting that it overtake traditional treatments, but it should be complementary, and it should be factored in at every stage.”

From suggested cocktails of psychobiotics for individual mental health complaints, to a run-down of the pro-biotic supplements available on supermarket shelves, The Psychobiotic Revolution includes tips on nourishing your microbiome to improve your mental health.

There are few real surprises when it comes to the dietary recommendations: processed foods and refined carbohydrates are out, and green leafy veg, wholegrains and fermented foods are in.

“It’s an old message,” Cryan says, “a message my grandmother talked about. But we’re putting the science behind it.”

The recent revelation that Ireland is the third highest country in Europe for the consumption of processed foods, Cryan says, is a cause for alarm. Apparently, almost half of the Irish diet is made up of “ultra-processed” foods.

“The impact that has is shocking. There are studies showing the association between processed foods and negative mental health. As a society, we need to wake up to this public health message.”

Eating for mood: Eat a varied diet with plenty of fresh fruit and vegetables.

A healthy microbiome is a varied one: lots of beneficial gut bacteria leaves less room for anxiety-inducing pathogens. Feed your gut bacteria on a wide variety of different foods, and include plenty of fruit and veg.

“By far the biggest psychobiotic contributor to your diet should be leafy greens and vegetables,” The Psychobiotic Revolution says.

Fibre is important: it’s indigestible to us, but feeds the microbes we want in our gut, that fight off pathogens, inflammation, and depression.

Eat fermented foods rich in probiotics. From yoghurt to kefir to sauerkraut, the health benefits of pro-biotic foods, that encourage the growth of beneficial gut bacteria, are well-known. But the psychological benefits are less well-known.

Two pro-biotics, lactobacillus and bifidobacterium, produce GABA (gamma-aminobutyric acid), a tranquilising neurotransmitter that can reduce anxiety. According to The Psychobiotic Revolution, “In one study, these bacteria, especially Lactobacillus rhamnosus, produced a result similar to Prozac, but without the side effects.”

Cut the junk: Foods with added sugar can induce depression, possibly by boosting pathogenic bacteria. For those with a sweet tooth, good quality maple syrup and honey are good alternatives, both with a potential psychobiotic boost.

There may be other reasons to avoid ultra-processed foods and additives that read like they’re from the science lab rather than the store-cupboard. Two emulsifiers commonly used in cakes and ice-cream, for example, have been shown to thin out your gut’s protective layer of mucus, which prevents pathogens burying themselves in the sensitive gut lining and causing inflammatory diseases linked with depression.

Breast is best: All John Cryan and Ted Dinan’s research points to how vital it is to establish colonies of beneficial bacteria in the gut from birth. A microbiome that is not diverse enough or that doesn’t contain enough of the “right” kind of microbes leaves the baby’s developing immune system open to pathogens getting into their blood supply via the lining of the gut: this is where the known link between bottle-feeding and increased lifetime risk of allergies and other immunological disorders comes in.

Breast milk contains oligosaccharides, complex sugars which are indigestible to the baby; they are actually designed to feed the baby’s microbiota. “When broken down, they also produce chemicals that are absolutely critical for brain development,” Cryan says. “It really puts forward the idea of early life being a primer for all aspects of health, including brain health.”


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