What is the gut microbiome and what factors influence it?

The gut microbiome can be thought of as an ecosystem much like a rainforest, where bacteria, fungi and viruses thrive – some good, some bad. The microbiome stabilises by around age three. Many factors affect our gut microbiome, including (but not limited to) our environment, genetics, and antibiotic interventions. 

The above factors influencing our gut microbiota are either difficult to manage or simply cannot be changed. However, the foods we consume can also significantly impact gut microbiota and are, importantly, modifiable. 

Although our gut microbiota are relatively stable, research shows that we can change their composition, for better or worse, within a matter of one day. 

To change the composition of our gut microbiota refers to either increasing or decreasing the overall amount (i.e., abundance) and/or types (i.e., diversity) of bacteria in our gut.

What role do gut microbiota play in diet?

We know that food choices are modifiable, and that food can rapidly change the composition of gut microbiota. There are some foods we are unable to digest, and we need our gut microbiota to do the job for us. 

Simple carbohydrates such as table sugar move through the stomach and into the small intestine where they are easily metabolised, digested and absorbed for energy by our bodies. However, when we eat fibre, it makes its way all the way through the small intestine and into the large intestine. The large intestine houses most of our gut microbiota and it is here that these microscopic bugs digest the fibre we were unable to access ourselves.

What foods best support a healthy gut microbiota composition?

Although we are yet to characterise exactly which bugs are needed for the optimal mix of gut bacteria, we do know that greater gut microbiota diversity is associated with better health outcomes. Fibre-rich whole-foods enhance the variety of gut bugs in the GI tract. Examples include plant foods such as vegetables, fruit, whole-grains, legumes, nuts and seeds. 

We can also promote a healthy gut by consuming bacteria itself in the form of fermented food such as kimchi, kefir, yogurt etc. The benefits associated with consuming fibre-rich food or fermented food are transient and will only last for as long as you are consuming them. This means that if we want to reap their health-benefiting rewards, we need to maintain their consumption as often as every day and ideally with every meal. The Ministry of Health recommends that New Zealand adults consume between 25 to 30 grams of fibre per day. Most of us are not reaching this target and are instead consuming less than 20 to 25 grams per day. A few simple steps to increase dietary fibre intake may include swapping white bread or white rice for whole-grain bread or brown rice, respectively. Moreover, by adding just two pieces of fruit to our snack pack or 1 cup of mixed vegetables with lunch or dinner may increase our fibre intake by 5 to 9 grams.

Feeding our gut microbiota essential complex carbohydrates promotes their ability to regulate our immune system; fight off invading pathogens; produce important nutrients; and, provide us with the extra energy we may need to pick ourselves up in the morning and make that much needed cup of coffee (among other important life things). Alternatively, a day-to-day diet lacking in fibre starves the gut microbiota and can lead to them eating the only food in sight – mucus that lines and protects our gut wall. Evidence suggests that if the gut microbiota munch down too deeply on this gut wall, our immune system as well as inflammatory processes may kick in.

The great thing about food choices is that we have several choices to make each day. The decision to include more fibre-rich foods in our diet can increase gut microbiota diversity and subsequently promote beneficial physiological outcomes.