The gut microbiome: How does it affect our health?

NEWSLETTER: Medical News Today

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? The bacteria in our gut are estimated to weigh up to 2 kg. 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 development of gut microbiota

Belief has long held that the development of gut microbiota does not start until birth, with the gastrointestinal tract of a fetus considered to be a sterile environment. According to Gut Microbiota Worldwatch – an information service created by the Gut Microbiota and Health Section of the European Society for Neurogastroenterology & Motility, a member of the United European Gastroenterology (UEG) – the digestive tract of a newborn is rapidly colonized with micro-organisms from the mother and the surrounding environment. An infant’s gut microbiota, for example, can be influenced by breastfeeding. Gut Microbiota Worldwatch explains that the gut of breastfed babies primarily consists of Bifidobacteria – considered a “friendly” bacteria that benefits the gut – while formula-fed babies are likely to have less of these bacteria. However, some studies have challenged the belief that the fetus is a sterile environment, suggesting that the development of gut microbiota begins before birth. A 2008 study published in the journal Research in Microbiology identified bacteria, including Enterococcus and Staphylococcus, in the early faeces of baby mice – known as the meconium – indicating the bacteria were transferred to the fetus from the mother’s gut during pregnancy. In this study, a group of pregnant mice was also inoculated with the bacterium Enterococcus fecium, which was isolated from human breast milk. The baby mice were delivered by Cesarean section 1 day before the predicted labour date, and their meconium was tested. The researchers identified E. fecium in their faeces, but no trace was found in the meconium of a control group. “Based on the sum of evidence, it is time to overturn the sterile womb paradigm and recognize the unborn child is first colonized in the womb,” Seth Bordenstein, a biologist at Vanderbilt University in Nashville, TN, told The Scientist last year.

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 are 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. Past research has suggested that a broader diversity of bacteria in gut is better for human health. A recent study reported by MNT, for example, found that infants with less diverse gut bacteria at the age of 3 months were more likely to be sensitized to specific foods – including egg, milk and peanut – by the age of 1 year, indicating that lack of gut bacteria diversity in early life may be a driver for food allergies. But the implications of a low-diversity gut microbiome do not stop there. You may be surprised to learn how lack of or overpopulation of specific bacteria may impact your health.

Obesity

More and more studies are looking at the association between the gut microbiome and weight gain, with some scientists suggesting the makeup of bacteria in the gut may influence an individual’s susceptibility to weight gain.