The human body is an ecosystem teeming with life. From the warm amazons of the armpits to the cool desert-like expanse of skin, cities of microbes breed, die and thrive in you.

Though the 21^st century likes to arm itself against germs with an arsenal of antibacterial wipes, hand sanitisers and sprays, microbes are an important part of who we are. Nowhere else can this be seen more clearly than in the close relationship humans have with their gut bacteria.

What is the microbiome?

Known as the microbiome, the unique community of bacteria living in your gut plays a vital role in a range of bodily functions, everything from aiding digestion and metabolism to influencing mood and immunity.

Humans have co-evolved with these gut bacteria and we function best when our bacteria do. It has been observed that the increased use of antibiotics in the last century has also seen an increase in many ‘modern’ diseases. Studies in children have shown the higher the number of antibiotic courses taken, the higher the risk of IBS, or inflammatory bowel syndrome, in those individuals.

Without crying witch-hunt on all antibiotics, their side-effects do go to show how important taking care of our microbiome is. If antibiotics show the extreme case of what happens when we wipe out our gut bacteria, you can imagine the things that go wrong when we neglect them in more subtle, everyday ways.

The microbiome and digestion

Our gut bacteria break down the food we eat. At the most basic level, this means bacteria can help us unlock essential nutrients in foods we don’t otherwise have the enzymes for. Gut bacteria provide us with some very important molecules, including the very important short chain fatty acids and a list of vitamins that reads straight off a fortified cereal box.

Having the microbiome also means that, despite what fitness diet tracker apps would have us believe, calories in does not equal calories out. Studies show that obese mice and humans have a less diverse population of bacteria, and that transferring this set of ‘obese’ microbiota to a normal mouse can lead to the same mouse gaining more weight, even on the same diet. In a reversal of the experiment, transferring the ‘skinny’ microbiota also led to decreased weight gain.

Bacteria and your brain

The activity of our microbiome can even impact our mood. The by-products of fibre digestion, for example, have been shown to increase levels of serotonin, a hormone associated with mood regulation.

This is because the gut has a direct pathway of neurons running to the brain, which communicates using a mixture of electrical and chemical signals. So while we and our bacteria munch happily away on fibre-rich plants, the by-products produced can act as chemical signals to activate different neural pathways to tell the body to produce more of a specific hormone.

What signals they produce depends on what bacteria live in your gut. Like with obesity, studies in mice show how behaviours of anxiety, stress and depression can be ‘transferred’ from one mouse to another with microbiome transplantations.

Microbiome and immunity

In a similar way, the microbiome ‘talks’ to the immune system to make sure it functions the way it should. The microbes we inherit during birth as we move through our mother’s vagina are extremely important in helping our immune systems develop properly as children.

Because our immune systems have evolved to work in the presence of these friendly bacteria, some scientists think that disrupting the community is what causes the immune system go on overdrive. Allergies are an example of this where the system rampages against harmless particles like dust. The principle can potentially be applied to a whole host of autoimmune diseases where the immune system is simply isn’t working the way it’s supposed to.

Caring for our microbiome

More and more, scientists are uncovering the myriad ways our health is affected by the once seemingly insignificant colony of bacteria in our gut.

Accompanying the growing excitement about the microbiome is a growing presence of probiotic-fortified yoghurts and fermented ‘superfoods’ on the shelves of health food stores.

While these interventions look like promising quick-fixes for a range of problems, the issue with many of these added-probiotic strain foods is that many of the strains chosen simply don’t survive long enough to produce any effect. Moreover, randomly throwing any ‘good’ bacteria at the body is akin to throwing paracetamol at everything regardless of what the actual ailment is.

On an everyday basis, the advice to building up a healthy microbial community is fairly simple: avoid empty high fat, high sugar foods, which is associated with a less diverse population of bacteria, and eat a balanced diet with lots of plants and lots of fibre. Remember, what feeds you is what feeds your microbiome.

The microbiome now and in the future

This isn’t to ignore probiotics and other microbiome-related interventions though. When done correctly, these interventions hold a lot of promise as a means of alleviating microbiome-associated ailments, and many exciting developments are taking place in the area.

Our microbiomes form a big part of who we are. It’s time we start recognising that and treating them with the care they deserve.

Shannon Doyle is an immunopharmacologist and founder of probiotic start-up Smart Flora.

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