Gut bacteria & brain function

by Daphne Lambert

A dynamic ecosystem of microbes lives in your gut and this complex microbiota is individual to you, a reflection of your journey through life, from what you eat to what you do and where you’ve been.

Microbiota-gut-brain axis

The knowledge that these microbes play a key role in maintaining a healthy immune system and good metabolic function is reasonably well known but more recently scientists have begun to understand just how important the gut microbiota are in normal, healthy brain function and how they could play a crucial role in a range of disorders including autism, ADHD, Parkinsons, anxiety and depression. The relationship between the gut microbiota and the brain is known as the microbiota-gut-brain (MGB) axis.

Research has shown that autistic people have a microbiome that differs significantly from those that are not autistic. Research with autistic children has shown that they tend to suffer from severe gastrointestinal problems possibly due to a disruption in gut flora leading to an overgrowth of pathogenic microorganism. 1, 2, 3

Evidence suggests that gut microbiota influences energy and weight. Obesity, generally considered a psychiatric disease, involves many pathways, but recently obesity has been studied in relation to the gut microbiome and the study found that obese people had microbiota demonstrably different from those that were not obese. 4, 5

Research has discovered a link between certain gut bacteria and the onset of Parkinson’s disease, basically scientists found that specific chemicals produced by certain gut bacteria worsen the accumulation of proteins in the brain associated with the disease. 6

A number of studies have shown how gut bacteria influence mood. Scientists have found that gut bacteria produce neurotransmitters such as serotonin, dopamine and GABA all of which play a key role in mood. It has been discovered that two strains of bacteria, lactobacillus and bifidobacteriums can influence anxiety and depression. John Cryan a neuroscientist at the University College of Cork in Ireland has studied, in animals, the effects of both of them on depression and demonstrated that these strains of bacteria reduced levels of hormones linked to stress. 7, 8

The microbiome affects the immune system which itself influences mood and behavior, so it is clear there are multiple mechanisms involved in the way microbes influence the brain.

Diet is a key element in a healthy microbiome. We can make a difference to the diversity and proper functioning of our gut microbiota every day with the foods we choose to eat.

Prebiotics and probiotics are two of the most widely studied elements in gut health.

Prebiotics are non digestible fiber compounds that provide food for the bacteria that live in the large intestine and encourage the activity of these beneficial microorganisms. Prebiotics are naturally present in a range of vegetables & fruit including garlic, onions, dandelion, leeks, asparagus, artichokes, apples and plums. In addition they are found in grains. Cooking changes the composition of the fibre so some, but not all, of the benefits will be lost with heating.

Probiotics are live microorganisms that provide a range of health benefits on the host, they seem to work through a variety of mechanisms including changing the function of microbes in the gut, inhibiting opportunistic pathogenic organisms and promoting microbiota stability. Probiotics have strength in numbers so you do have to consume plenty to see the benefits. Probiotics come from the

bacteria found in lacto fermented foods so a diet that includes plenty of fermented vegetables is particularly beneficial. In addition fermented milks contain important bacterial species that can be of benefit. Nearly every culture has a history of some kind of fermented dairy product. In the west cow’s milk is the most popular milk used followed by goat, ewe and buffalo, but around the world other mammals are milked including mares, camel, llamas and reindeer.

Long before scientists began to unravel the vast complex world of microbes our ancestors with fermenting traditions were harnessing the power of foods rich in probiotics.

Today science has shown that the gut microbiota play a key role in our wellbeing and more of its vital importance has become understood.



3 Theoharides TC, Athanassiou M, Panagiotidou S, Doyle R. Dysregu- lated brain immunity and neurotro- phin signaling in Rett syndrome and autism spectrum disorders. J Neuro- immunol. 2015




7 Emeran A. Mayer, Rob Knight, Sarkis K Mazmanian, John F Cryan & Kirsten Tillisch Gut Microbes and the Brain: Paradigm Shift in Neuroscience 2014