by Lily Roberts, Centre for Health Policy, Institute of Global Health Innovation
Did you know that not only does your gut do an incredible job of nourishing you by digesting your food, but that the composition of your resident gut bacteria also has a profound impact on your quality of life? While some of the specific mechanisms are still to this day unclear, a plethora of significant research is out there, with answers to our burning questions on how our gut bacteria can affect us.
On day one, the human body is exposed to a multitude of bacteria via the birthing canal. These bacterial cells colonise our body at a ratio of 10:1 with our own cells, most of which taking residence in the gut. Those that make themselves at home in our gut are referred to as our ‘microbiota’ (roughly translating to tiny living things). The relationship between the human body and these cells which make up our microbiota is referred to as ‘symbiotic’, which simply means both parties benefit from co-existing. It turns out our microbiota responds directly to the food supply by encouraging growth of either beneficial bacteria or harmful bacteria. This means that if we choose to eat nourishing whole, natural, unprocessed foods, our beneficial gut bacteria will thrive. If we constantly feed ourselves processed foods like hamburgers and chips, harmful bacteria that thrive on these foods will take over the gut and wreak havoc, impeding growth of beneficial bacteria. Ever heard of the phrase ‘you are what you eat’?
So why is it in our best interest to encourage the colonisation of these good bacteria? Well, there is some evidence that the gut microbiota interacts with the brain in both directions via the vagus nerve and through tiny messengers called neurotransmitters, bacterial metabolites, and cytokines, as pictured. Through these pathways gut bacteria can influence our health status, our emotions, and our food choices.
Benton, Williams, and Brown (2), in their 2007 randomised controlled trial on 132 healthy humans, investigated whether consuming a milk drink containing a probiotic had any effect on mood. While the probiotic had a negligible effect on those with a generally good mood to begin with, participants who began the study with low mood reported feeling happier after consuming the milk drink. This is an exciting find, as it suggests enhancing the variety of our gut bacteria by simply consuming a probiotic can pick us up when we’re feeling low. So there’s a case of ‘healthy’ gut composition resulting in a positive change of emotions, but what happens when the coin is flipped?
A 2014 review by Bailey (1) investigated how this axis of gut-brain interaction can function in both directions. Studies on mice showed that when stress was induced by the experimenters, normal healthy gut microbiota was disrupted, and this led to infection of the gut by harmful bacteria and subsequent inflammation, which can be very damaging in excess. This brain-to-gut pathway then triggered a gut-to-brain pathway which brought on anxiety-like behavior. The destruction brought on by the preliminary stressor could be ameliorated simply by applying probiotics (available in supplemental or dietary form), which restored homeostasis to the gut. The results of this review suggest significant links between not only microbiota and our emotions, but also our immunity.
Claesson et al. (3) in their observational studies of the elderly found that those in care homes had significantly less diverse microbiota than those living in a community setting. This outcome was thought to be due to the more varied diets of those living in the community, encouraging growth of a wider range of bacteria. Those in care homes living with less diversity amongst strains of bacteria in their gut showed increased frailty, co-morbidity, markers of inflammation, and poorer nutritional status. This suggests that the bacterial makeup of the gut may have a significant effect on decline in health while ageing. This information would prove particularly useful for those in charge of designing food programmes for care homes. It’s in our best interest to ensure our parents, grandparents and great-grandparents are as healthy as possible in their final stage of life, and feeding them a variety of nutritious foods seems to be a plain and simple method of achieving this.
An interesting experiment in 2010 by De Filippo et al (4) investigated the discrepancy in microbiota make-up between children from urban Europe and rural Africa. They took fecal samples from 29 children, then analysed the bacterial content. The data obtained from these samples showed that the high-fibre, mainly plant sourced diets of the African children cultivated a completely different microbiota to the European children who were consuming a ‘western diet’ which is typically high in animal protein, fats, and sugar, and low in plant fibre. The figure to the right shows the extent of the differences between these two groups, with a different colour representing a different species of bacteria. Over 70% of the microbiota of the African children (top chart) was represented by 2 species of Bacteroidetes – Prevotella and Xylanibacter – which contain bacterial genes for cellulose and xylan hydrolysis, particularly helpful for breaking down polysaccharide-rich fibres that are found in plant foods. The European children (bottom chart) were completely lacking in these species. The main point we can take from this study is evidence that our gut bacteria evolve as a result of their diet, and the reason for this is to maximize the energy we can obtain from our food.
So take care in choosing an appropriate diet for your lifestyle with your gut bacteria in mind. They are working around the clock for you every day, and if you choose the right foods the majority of the time (natural, whole, unprocessed) they will flourish and ward off any bad competitors that come their way in order to keep you healthy and happy.
References
Bailey MT. Influence of stressor-induced nervous system activation on the intestinal microbiota and the importance for immunomodulation. Adv Exp Med Biol. 2014;817:255-76. doi: 10.1007/978-1-4939-0897-4_12.
Benton D, Williams C, Brown A. Impact of consuming a milk drink containing a probiotic on mood and cognition. Eur J Clin Nutr. 2007;61(3):355-61. Doi: 10.1038/sj.ejcn.1602546
Claesson MJ, Jeffery IB, Conde S, Power SE, O’Connor EM, Cusack S, et al. Gut microbiota composition correlates with diet and health in the elderly. Nature. 2012;488:178-184. doi:10.1038/nature11319
De Filippo C, Cavalieri D, Di Paola M, Ramazzotti M, Poullet JB, Massart S, et al. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa.
PNAS. 2010;107(33):14691-6. doi: 10.1073/pnas.1005963107
Mayer EA, Knight R, Mazmanian SK, Cryan JF, Tillisch K. Gut Microbes and the Brain: Paradigm Shift in Neuroscience. Journal of Neuroscience. 2014;34(46):15490-6. Doi: https://doi.org/10.1523/JNEUROSCI.3299-14.2014