The Influence of Diet and Probiotics on the Intestinal Microbiome - Essay Example

The influence of diet and probiotics on the intestinal microbiome It is a well known fact that human body contains microbial cells that are tenfold more in number than the number of cells in the human body (Gerritsen, Smidt, de Vos, 2011). These organisms colonise several sites including the gastrointestinal tract, which is the most densely colonised organ. Bacteria constitute majority of all the microbial cells present in the gastrointestinal tract of human beings. Various culture-dependent and independent studies have demonstrated that most of the intestinal bacteria belong to the two phyla Firmicutes and Bacteroidetes (Hemarajata and Versalovic, 2013). These microbiota are influenced by various external factors and internal factors. Some of the external factors which are widely studied and are interesting for human health are diet and probiotics. In this essay, influenceof diet and probiotics onintentinal microbiota will be discussed. The intestinal microbiota play a major role in the various nutritional, immunological, physiological and metabolic processes of the human body. Certain dietary polysaccharides are indigestible and intestinal microbiota extract energy from these resistant starches and fibers. Such metabolic activities cause release of various vitamins like vitamin K, folic acid and B12, short chain fatty acids and various aminoacids which are not produced in the human body. The microbiota also participate in various pathogenic defence mechanisms like resistance of colonisation and production of various compounds with antimicrobial properties. The microbiota are also involved in the maturation, development and maintenance of various sensory and motor functions of the gastrointestinal tract, the barrier system of the intestine and also the immune system of the intestinal mucosa (Gerritsen et al, 2011). According to the Food and Agricultural Organization of the United Nations and the World Health Organization (cited in Hemarajata and Versalovic, 2013), probiotics are defined as ‘living microorganisms, which when administered in adequate amounts confer health benefits on the host.’ The most commonly used probiotics are Bifidobacterium and lactobacillus. Other probiotics in market include certain species of enterococcus, streptococcus, propionibacterium and bacillus. Yeast like Saccharomyces are also used as probiotics. The probiotic organisms interact with the intestinal microbia either directly or through enzymatic action. They interact directly with the epithelial and mucosal layer of the intestine and thereby influence the functions of the intestinal barrier and also the immune system. Probiotics can also have effects outside the gastrointestinal tract. They can trigger the systemic immunity appropriately and have health beneficial effects on the brain and liver too. Probiotics modulate the intestinal microbiota through various mechanisms like reduction of the pH of the lumina, offering competition for nutirents, secreting certain anti-microbial compounds known as bacteriocins, prevention of adhesion of pathogeneic bacteria to the luminal wall, prevention of evasion of epithelial cells, induction of certain compounds like defensins in the host which have antimicrobial properties and such other mechanisms. Transient colonisation of the probiotic organisms have been noted in various studies. However, it is yet unclear whether colonisation is critical for exertion of health benefits through the aforesaid mechnisms. In diseased individuals, probiotics modulate the intestinal microbiota in such a way that a healthy composition of microbiota of the intestine is achieved. It is however, difficult to interpret the effects of probiotics in individulas who are healthy (Gerritsen et al, 2011). Certain molecular approaches in research about probiotics have helped gain insight into the role of probiotics in diseased states. One such research has pointed to the potential benefits of probiotic supplementation with Lactobacillus rhamnosus in the prevention of asthma through suppression of development of early markers of the disease. This effect is thought to be due to the interaction between the mucus binding pili and the host. Lactobacillus rhamnosus is also known to stimulate functionally reduntant microbiota that are stable and even and also facilitate the colonisation of other microorganisms that are beneficial. However, it is yet unclear whether this benefit is because of the pilial ability of the organism to bind to the mucosal surfaces of the intestine. Through metagenomic sequencing, it was possible to understand that consumption of Bifidobacterium animalis inthe form of fermented milk can induce certain metabolic shifts in ulcerative colitis (Gerritsen et al, 2011). There is a mutual relationship bettwen the microbiota of the intestine and the human host and this is significantsly influenced by the diet. Various nutrients that are consumed in the form of diet affect the structure of the microbial community and proide various substrates essential for the metabolism of the microbes. The end result of these metabolic processes are certain small molecules which are absorbed by the host and cause many important physiological processes. Differences in the physiological effects of these molecules have been well studied while comparing many constrasting diets like breast milk versus formula milk, Agarian plant-based diet versus Western diet, etc (Albenberg and Wu, 2013). Diet has influence on the activity and structure of various microorganisms that reside in the gut of human beings. The influence varies from diet to diet. Diets which are mainly animal-based increase various bile-tolerant organisms like Bilophila, Alistipes and Bacteroides. At the same time, such diets reduce the levels of Firmicutes which are involved in the metabolism of various dietary plant polysachharides like Eubacterium, Ruminococcus and Roseburia. There is evidence that animal based diet increases both the activity and the abundance of Bilophila wadsworthia supporting the link between dietary fat, bile acids and outgrowth of microbiota that are involved inthe pathogenesis of inflammatory bowel disease (David et al, 2013). Diet plays a major role in the metabolism and composition of various microbiota of the intestine. The type, balance and amount of various micromutrients and macronutrients have a major impact on these microbiota. The bacteria have certain enzymes which are capable of degrading various complex dietary substrates. When dietary carbohydrates are metabolised, certain short chain fatty acids and gases are released. The main end products of metabolism are propionate, acetate and butyrate. These lower the pH of the intestine. This acidic environment further influences the composition of the microbiota, inturn affecting the health of the host. Metabolism of proteins by microbiota can release additional fermentation products which are detrimental to the health of the host (Scott et al, 2013). Diets rich in fermentable fiber alter the ratio of Firmicutes to Bacteroides and thus change the composition of the microbiota of the gut. These microbiota metabolise the fiber and increase the concentration of short chain fatty acids. These short chain fatty acids entered the circulation and decreased allergic airway disease (Trompette et al, 2014). Thus, diet and probiotics alter the intestinal microbiota and contribute to various health effects. References Albenberg, L.G., and Wu, G.D. (2013). Diet and the Intestinal Microbiome: Associations, Functions, and Implications for Health and Disease. Gastroenterology, S0016-5085(14)00149-8. Retrieved on 22nd March 2014 from www.pubmed.com David, L.A., Maurice, C.F., Carmody, R.N., et al. (2013). Diet rapidly and reproducibly alters the human gut microbiome. Nature (12), 5-7. Retrieved on 22nd March 2014 from www.pubmed.com Gerritsen, J., Smidt, H., and de Vos, W.M. (2011). Intestinal microbiota in human health and disease: the impact of probiotics. Genes and Nutrition, 6(3): 209–240. Retrieved on 22nd March 2014 from www.pubmed.com Hemarajata, P., and Versalovic, J. (2013). Effects of probiotics on gut microbiota: mechanisms of intestinal immunomodulation and neuromodulation. Therap Adv Gastroenterol., 6(1), 39–51. Retrieved on 22nd March 2014 from www.pubmed.com Scott, K.P., Gratz, S.W., Sheridan, P.O., Flint, H.J., and Duncan, S.H. (2013). The influence of diet on the gut microbiota. Pharmacological Research, 69(1), 52-60. Retrieved on 22nd March 2014 from www.pubmed.com Trompette, A., Gollwitzer, E.S., Yadava, K., et al. (2014). Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis. Nature Medicine, 20, 159–166. Retrieved on 22nd March 2014 from www.pubmed.com Read More