Diet and the microbiome

Over the last few decades, consumption of the Western diet has coincided with an increase in the prevalence of chronic metabolic and inflammatory diseases such as Colorectal cancer (CRC), Hidradenitis suppurativa (HS) and Type II diabetes mellitus (T2DM). Patients harbouring these diseases have an altered microbiota composition when compared to controls. Meanwhile, specific taxa have been identified as directly contributing to their pathogenesis. Specific dietary components have been identified as beneficial or detrimental to host health through microbiota dependent and independent mechanisms. Dietary manipulation of the microbiota has shown promising potential in disease prevention and treatment. Furthermore, evidence suggests that the microbiota has potential to be used as a biomarker for diagnosis, prognosis or risk profiling of different diseases. However, to precisely and effectively use diet and/or microbiota-based therapies in a clinical setting more must be learned about how each factor influences each other and the host. With respect to these research questions, this thesis aims to better understand diet and the microbiome in the setting of metabolic and inflammatory disease. We show that the majority of patients who underwent surgical resection for CRC had a microbiota composition that was most similar to patients newly diagnosed with CRC while, in one third of patients the microbiota reverted toward normal. Interestingly, the consumption of the fibre-rich and chemoprotective cruciferous vegetables co-varied with differences in microbiota composition. We also describe how 40% of patients with HS have a microbiota composition similar to patients with Crohn’s disease (CD) while the remaining 60% have a microbiota composition most similar to controls. Interestingly, patients with a CD-like microbiota configuration consumed significantly more carbonated soft drinks than those with a normal microbiota composition. Finally, we show that dietary fibre (yeast β-glucan) exerted a hypoglycaemic effect in patients with T2DM when compared to the placebo control. Significant differences in fasting gluose and insulin coincided with enrichment of fecal bile acids in patients administered yeast β-glucan including tauroursodexoycholic acid which is known improve glucose control and lower insulin resistance. Overall, these findings highlight diet-microbiome associations and risk development of disease. We also demonstrate the use of diet as an effective therapy to alleviate metabolic and inflammatory disease.