Healthy gut, healthy brain?

Our intestines contain up to 1,000 different species of bacteria, viruses, fungi and other microorganisms (microbes for short), and up to 100 trillion of them make up our individual gut microbiome. Altogether they weigh around 1 to 2 kilos, and as well as helping us digest our food, these microbes are involved in balancing the good versus bad bacterial composition, manufacturing neurotransmitters such as serotonin, synthesizing vitamins like B12 and vitamin K, and regulating our immune system.

Babies receive their first microbiome from their mother, which will differ according to how the baby is delivered and whether it’s breast fed. By the age of three an infant’s gut microbiota resembles that of an adult, then, as we get older, new microbes are introduced via our diet and other environmental factors. Some of these may improve our microbiota, while others such as poor diet, frequent alcohol, tobacco smoke, and antibiotics, may harm it and lead to a loss of balance and diversity, commonly referred to as ‘dysbiosis’.

Can our gut affect our mental health?

In recent years, the effect of the gut microbiome on an individual's general health and well-being, and brain health in particular, has become a growing topic of interest.

A pivotal study published by Japanese Professor Nobuyuki Sudo in 2004 found that mice raised in a sterile environment which prevented bacterial colonization of their intestines, demonstrated exaggerated physiological reactions to stress compared to mice raised in normal conditions. He also found that these abnormal reactions could be reversed through probiotic-induced bacterial recolonisation. This led to the discovery of the gut microbiome's causal involvement in the development of the hypothalamic–pituitary–adrenal (HPA) axis, which controls the body’s stress response and is one of the most important components of the gut-brain axis. It had been known for some time that physical and psychological stress could affect the composition of intestinal microbiota, but this was the first study that indicated the interaction could work both ways (bidirectional), and that the composition of the gut could potentially affect our mental as well as our physical health.

What are Psychobiotics?

The intervening years have seen a considerable amount of research into whether Professor Sudo’s results would be replicated in human trials. Several studies have found that patients with a wide variety of physical and psychological conditions show distinct compositional changes in their gut microbiome. At the forefront have been Professors John Cryan and Ted Dinan from University College Cork, Ireland, who, in 2013 coined the term ‘psychobiotic’ to refer to the probiotics, prebiotics and postbiotics that might, by improving the health of the gut microbiome, also potentially be used to prevent and treat various neuropsychiatric disorders, including depression, autism, and schizophrenia, as well as neurodevelopmental and neurological diseases such as Attention-Deficit Hyperactivity Disorder, Alzheimer's disease, Parkinson's disease, Huntington's disease, Anorexia Nervosa, and Multiple Sclerosis.

What does the research show?

The research into psychobiotics is in its infancy, and although most of the research acknowledges their therapeutic potential, particularly strains of Lactobacillus and Bifidobacterium, they also point to the need for further investigation involving larger and more diverse sample sizes. You can read more about the potential therapeutic impact of psychobiotics on mental health here, and a review of the effectiveness of psychobiotics in the treatment of psychiatric and cognitive disorders here.

Should I take psychobiotics?

Despite the lack of conclusive evidence, psychobiotics are now widely marketed as an over-the-counter treatment to reduce stress and improve mood. This is permitted because probiotics are considered to be food supplements, not drugs. A lack of regulation means that manufacturers don’t have to prove the quality, or even the contents of their products, which means that there's no way to know if the bacteria are still active at the point of consumption, and even if they are, whether they can survive our stomach acid! In addition, each person will have different types and numbers of bacteria in their gut, which means the probiotic that works for one person might not work for another. Fortunately, these supplements appear to be safe for healthy people to take, although there’s a small risk for those with a weak immune system.

Psychobiotic diet

Because our microbes are reliant on what we feed them, a more reliable and natural way to improve our gut microbiota and also promote good mental health, is to follow a psychobiotic diet by eating a wide variety of fibre-filled vegetables (garlic, leeks, cabbage, onions), fruits (apples, bananas, berries, avocados), grains (oats, barley, bulgar), legumes (beans, lentils, chickpeas), and fermented foods (yogurt, kefir, kimchi, sauerkraut).

A psychobiotic diet also discourages the consumption of unhealthy foods like sweets, fast food, and sugary drinks. You can read more about feeding your microbes here.

Conclusion

Although it's still too early to determine the exact role of psychobiotics in relation to the gut-brain axis, from the evidence so far, it seems likely that they not only support a healthier gut, but a healthier brain as well. As the psychobiotic diet is very similar to the mediterranean diet (recommended by nutrition experts and the World Health Organization), there’s nothing to lose, and a lot to gain, by giving it a try. Bon Appetit!

Thank you for reading this blog post. If you have any tips or information that you’d like to share, or ideas for future posts, please do let me know. I would love to hear from you.