Unveiling implications of fecal microbiota on human's cardiometabolic health: role of physical activity and fitness

Resum

The microorganisms that colonize the gastrointestinal tract are known as gut microbiota, being bacteria the microorganisms that are found in higher abundance. Bacteria communities regulate host metabolism by producing metabolites that interact with specific receptors on different tissues modulating the host's health. In fact, the alteration of these bacteria communities within the intestine has been observed in individuals with cardiometabolic disease. Thus, strategies aiming to modify the relative abundance of these gut bacteria have been suggested as novel therapies for the prevention and treatment of cardiometabolic diseases. One of the most promising strategies for modulating gut microbiota is increasing levels of physical activity and fitness, yet the scientific evidence is limited. The present International Doctoral Thesis aims to determine the relationship of novel cardiometabolic risk markers (i.e., endocannabinoids and brown adipose tissue) with fecal microbiota diversity and composition and to study the association of physical activity and fitness levels with fecal microbiota diversity and composition in humans. To unravel these aims, we conducted four cross-sectional studies (Studies I, II, III and V) and one case-control study (Study IV) in humans. The results show that plasma levels of endocannabinoids and their analogues positively correlate with the relative abundance of bacteria belonging to Firmicutes and Verrucomicrobia phyla which are involved in the regulation of gut barrier integrity (Study I). Interestingly, these bacteria communities negatively correlate with brown adipose tissue volume and activity (Study II). Higher physical activity levels, especially of vigorous intensity, are associated with higher fecal diversity and relative abundance of certain fecal bacteria (Study III). Particularly, we found differences in fecal microbiota composition between resistance and endurance athletes as well as with sedentary individuals (Study IV). Lastly, higher physical fitness levels are associated with a higher relative abundance of certain fecal bacteria in both young and older adults (Study V). The present International Doctoral Thesis provides new insights into the understanding of human gut microbiota, and show that endocannabinoids may improve the gut barrier integrity through certain fecal bacteria. Interestingly, these bacteria communities may be involved in the regulation of human brown fat metabolism. Moreover, the observed association of physical activity and fitness with fecal microbiota diversity and composition provide hope for future intervention strategies aiming to potentially modify gut microbiota in humans.