11 March 2015 - MNT - The gut microbiome: how does it affect our health?

We can carry up to 2 kg of microbes in our gut. Within the tens of trillions of micro-organisms that live there are at least 1,000 species of bacteria consisting of over 3 million genes.

What is more, two thirds of the gut microbiome - the population of microbes in the intestine - is unique to each individual. But do you know how your gut microbiota could be influencing your health?

Most of us are aware that the bacteria in our gut play an important role in digestion. When the stomach and small intestine are unable to digest certain foods we eat, gut microbes jump in to offer a helping hand, ensuring we get the nutrients we need.

In addition, gut bacteria are known to aid the production of certain vitamins - such as vitamins B and K - and play a major role in immune function.

But increasingly, researchers are working to find out more about how gut bacteria - particularly the bacteria that is unique to us individually - influence our health and risk of disease.

Perhaps most studied is how gut microbiota affects an individual's risk of obesity and other metabolic conditions. In November 2014, for example, Medical News Today reported on a study claiming our genetic makeup shapes what type of bacteria reside in our gut, which may affect our weight.

In this Spotlight, we take a look at obesity and some of the other - perhaps surprising - health conditions that may be driven by our gut microbiota.

The more diverse our gut bacteria, the better

While the debate over whether infants are born with gut bacteria continues, it seems scientists are in agreement about one thing: from birth until old age, our gut bacteria is constantly evolving.

As mentioned previously, two thirds of the gut microbiome is unique to each person, and what makes this unique is the food we eat, the air we breathe and other environmental factors. Some studies have even suggested the makeup of the gut microbiome is influenced by genes.

But how does this unique gut bacteria affect our health? This is a question that researchers have become increasingly interested in answering.

Mental Health

Not many of us are likely to think about how gut bacteria affect the mental state, but they actually play a very important role.

According to the American Psychological Association (APA), gut bacteria produce an array of neurochemicals that the brain uses for the regulation of physiological and mental processes, including memory, learning and mood. In fact, 95% of the body's supply of serotonin is produced by gut bacteria, according to the APA.

With this in mind, it is perhaps unsurprising that gut bacteria has been associated with a number of mental health problems, including anxiety disorders and depression.

Autism

Autism is estimated to affect 1 in 68 children in the US. While studies have associated environmental factors - such as pollution - and genetics as potential causes of the disorder, researchers are increasingly looking at the role of gut bacteria in its development.

In 2013, a study by researchers from Arizona State University found that children with autism possessed lower levels of three types of gut bacteria - Prevotella, Coprococcus and Veillonellaceae - compared with children free of the condition.

A more recent study from the team found that concentrations of specific chemicals produced by gut bacteria - called metabolites - in fecal samples of children with autism differed to the concentrations found in the fecal samples of children without the disorder.

This led the researchers to hypothesize that gut microbes alter the metabolites associated with communication between the gut and the brain, which interferes with brain function.

Further strengthening the association between gut bacteria and autism is a 2013 study published in Cell that found the bacterium Bacteroides fragilis reduced autism-like symptoms in mice.