Whether you are aware or not, your gut is home to a complex ecosystem of about 100 trillion microbes. These bacteria which are collectively know as the microbiome, out number your own body cells by 10 times and they are so integral to the functioning of your body that it is often referred to as the ‘forgotten organ’ (1).
In the beginning
Microbiota are opportunistic so from the moment we are born they start to colonise in our gastrointestinal tract. A baby born through the birth canal will have differences in diversity and composition of bacteria compared to a caesarean birth due to initial exposure of microbes. Composition is then further modulated through diet (2). Breast fed infants tend to have a dominance of Bifidobacteria whereas formula fed infants acquire a more diverse microbiota and tend to have lower numbers of Bifidobacteria and Lactobacilli both of which are known to be beneficial to human health. The introduction of food then influences colonisation towards an adult composition, particularly by increasing in Firmicutes (4). The original bacteria have the ability to effect gene expression of the gut cells. This allows them to create a favorable environment for their own existence, which can subsequently prevent the growth of other bacteria introduced into the ecosystem. Therefore the initial acquisition of bacteria determines the final composition in adults (2). The composition of adult microbiota tends to remain stable over time although it is vulnerable to our exposure to chemicals, toxins, medications, stress and particularly diet (5).
Feeding your bugs
The mutual relationship between you and your microbiota is heavily influenced by what food you eat. Eating nutrients affects the structure of the microbial community and provide substrates for microbial metabolism. According to Sonnenburg E. and Sonnenburg J. (6) a typical Western diet is low in “microbiota-accessible carbohydrates (MACs)” and as a result may contribute to development of inflammatory diseases. MACs include fruits, vegetables, starchy plants, nuts, seeds, legumes, and other foods that are poorly absorbed, but can be utilised as a food source by our intestinal bacteria. They include what are more commonly know as ‘prebiotics’, which by definition are indigestible carbohydrates: oligosaccharides, resistant starch, and non-starch polysaccharides. Polysaccharides undergo a fermentation process to yield short-chain fatty acids (SCFA), which can then be absorbed and metabolised. SCFAs acetate and propionate are involved in metabolic processes lipogenesis and gluconeogenesis respectively. Butyrate, another SCFA, is the dominant substrate for the microbiota energy production (7). The production of these weak acids reduces the pH of the colon inhibiting the growth of pathogens (8). Prebiotic foods have been found to have numerous positive effects on health such as improved intestinal function, and reduced risk of intestinal infections, type 2 diabetes, obesity, metabolic syndrome, and colon cancer (9). Interestingly it is not only the typical Western diet that is low in prebiotic foods. Very low carbohydrate diets, and particularly ketogenic diets, tend to exclude these foods due to their moderate to high carbohydrate content. This can starve the beneficial bacteria and may potentially lead to a bacterial imbalance or dysbiosis. Those that follow a low carb diet should be encouraged to consume non-digestible, fermentable fibers like resistant starch and non-starch polysaccharides that don’t count toward daily carbohydrate intake.
Just eat real food
To ensure we encourage a good balance of the right types of bacteria, the best place to start is by eating real food. Over consumption of the wrong types of foods, particularly refined carbohydrates, can lead to an increased presence of lipopolysaccharide (LPS) found on the surface of bacteria which triggers an immune response and contributes to the low grade chronic inflammation associated with metabolic disorders (10). Microbiota composition has been found to be a contributing factor to the pathophysiology of obesity by enhancing the energy harvested from the diet. Obese people have a change in the balance of Bacteroidetes and Firmicutes (the two dominant bacterial species), which allows for increased energy extraction from food resulting in higher SCFA production and absorption. Consequently greater energy is produced (10). Eating a natural whole and unprocessed diet which by default is lower in carbohydrates, higher in healthy fats and high in fiber, encourages the right balance and ensures your gut bacteria are working in your favour.
Eat some good bacteria
The implications of microbiota in health and especially disease have resulted in growing interest in therapeutic strategies to combat dysbiosis. Eating probiotic foods or taking probiotic supplements promotes the activity of beneficial species and therefore improves the symbiotic relationship between us and our bacteria (8). The centuries old practice to eat probiotic containing fermented foods has regained popularity in recent years. In fermentation, good bacteria turn sugar molecules into lactic acid and in doing so are able to multiply and proliferate. The lactic acid creates an acidic environment that protects the fermented food from being invaded by harmful bacteria with a higher pH. The addition of probiotic rich foods to your diet such as yoghurt containing live cultures, sauerkraut, kim chi, miso, tempeh, kefir, kombucha, and apple cider vinegar helps to sustain a healthy microbiome. It is particularly important for those who have taken antibiotics to not only include these in their diet but to additionally take a probiotic supplement. Probiotics have the ability to reestablish wiped out bacterial species as well as reduce the incidence of antibiotic associated diarrhea in both children and adults (2).
As research continues, evidence consistently indicates the importance of diet on nurturing our microbiome to support overall health. In respect to this, it would appear we have the power to directly influence our health by modulating and maintaining a healthy microbiome through what we choose to eat.
- O'Hara, A. M., & Shanahan, F. (2006). The gut flora as a forgotten organ. EMBO reports, 7(7), 688-693.
- Guarner, F., & Malagelada, J. R., (2003). Gut flora in health and disease. The Lancet, 360, 512-519.
- Foster, J. A., & Neufeld, K. A. M. (2013). Gut–brain axis: how the microbiome influences anxiety and depression. Trends in neurosciences, 36(5), 305-312.
- Duncan, S. H., & Flint, H., (2013). Probiotics and prebiotics and health in ageing populations. Maturitas, 75(1):44-50.
- Artis, A., (2008). Epithelial-cell recognition of commensal bacteria and maintenance of immune homeostasis in the gut. Nature Reviews, Immunology, 8, 411-420.
- Sonnenburg, E. D., & Sonnenburg, J. L. (2014). Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell metabolism, 20(5), 779-786.
- Scott, K.P., Gratz, S.W., Sheridan, P.O., Flint, H.J., & Duncan, S.H., (2013). The influence of diet on the gut microbiota. Pharmacological Research, 69, 52-60.
- Alonso, V.R., & Guarner, F. (2013). Linking the gut microbiota to health and disease. British Journal of Nutrition, 109, S21-S26.
- Roberfroid, M., Gibson, G.R., Hoyles, L., McCartney, A.L., Rastall, R., Rowland, I,... Meheust, A. (2010). Prebiotic effects: metabolic and health benefits. British Journal of Nutrition, 2, S1-63.
- Turnbaugh PJ, Hamady M, Yatsunenko T, Cantarel BL, Duncan A, Ley RE, Sogin ML,... Gordon, J.I. (2009). A core gut microbiome in obese and lean twins. Nature, 457, 480-484.