**3. Dysbiosis of gut microbiota during endurance performance**

The dysbiosis in the GM is linked to various pathophysiological conditions such as intestinal disorders (inflammatory bowel disease, coeliac disease, irritable bowel disease) and extra-intestinal disorders (allergy, metabolic syndrome, asthma, cardiovascular disease, obesity, oxidative stress) [47]. The beneficial bacteria play an essential role in controlling the fermentation and absorption of dietary nutrients such as SCFAs [48]. The dysbiosis in the microbiota influences the development of disease which involved the pivotal mutualistic relationship between colonic microbiota, their metabolic product and the host immune system. Recent evidence has implicated the influence of excessive exercise on GM dysbiosis [49]. Studies in mice found that excessive exercise negatively impacts immunity, substance and energy metabolism, and gut microbial diversity [50].

Generally, it is believed that exercise is beneficial for the gut, but athletes with regular training and exercise have been reported to experience gastrointestinal disorders termed exercise-induced gastrointestinal syndrome. The frequency of developing the syndrome depends on numerous factors like sport type, the intensity of exercise, gender and syndrome often observed: loose stool, diarrhea, abdominal pain, intestinal bleeding in the lower digestive tract [51, 52]. There are two pathways suggested as causative for this disorder: Circulatory- gastrointestinal pathway and neuroendocrine-gastrointestinal pathway. In Circulatory-gastrointestinal pathway, high intensity exercise cause gut ischemia–reperfusion, which is a factor associated with site specific oxidative stress intestinal injury and in Neuroendocrinegastrointestinal pathway, both physical and psychological stresses alter the gut motility and transit through enteric nervous activity which causes gut malabsorption of nutrients [53–55]. Studies found that intense endurance running (triathletes) lead to malabsorption of carbohydrates [27]. Evidence suggests that female endurance runners had a higher abundance of inflammation related bacteria and a higher concentration of succinate in the intestinal lumen due to dysbiosis, thus affecting the endurance performance [56].

#### **3.1 Energy metabolism**

During endurance exercise, energy availability is the essential limiting factor, and restoring the cellular energy homoeostasis is a must. There is a complex relationship between gut microbiota and host's energy metabolism. Gut microbiota increases the ability to harvest the energythe energy from digested food, thereby producing metabolites and microbial products (SCFA, secondary bile acids, and lipopolysaccharides). These microbial products will later modulate appetite, energy uptake and storage, gut motility and energy expenditure [57]. Healthy gut microbiota can exert positive effects in athletes. One of the studies reported that physical exercise and associated dietary adaptation are linked with changes in the gut microbial diversity [58]. Supplementation of probiotic bacteria *Lactobacillus plantarum* TWK10 improves energy metabolism. It transports the host fatty acid to the organ via bloodstream, further metabolized in the mitochondria to generate energy [59].

#### **3.2 Immune response**

During endurance exercise, immune response activation plays an important role. Some evidence suggests that, prolonged periods of intense exercise suppress the immune response, including monocyte, granulocyte, leukocyte count, and serum immunoglobulin levels among individuals [60]. Intense exercise training

*The Interaction between Dietary Components, Gut Microbiome, and Endurance Performance DOI: http://dx.doi.org/10.5772/intechopen.97846*

increased the number of pro-inflammatory cytokines, also anti-inflammatory modulator, intestinal lymphocytes. These will lead to the fluctuation of gut microbiota diversity and in their secreted metabolites, increase hyperthermia, gastrointestinal permeability, destruction of gut mucous membrane thickness and weakens the activity of antioxidant enzymes [61]. Studies found that strenuous exercise suppresses the lymphocytes proliferation, levels of secretory IgA in saliva and modulates the synthesis of inflammatory cytokines [62]. Studies suggest that monitoring the gut microbiota diversity and modulating it by the supplementation of probiotics and prebiotics will be more cost effective compared to the utilization of drugs [63].

#### **3.3 Oxidative stress**

During endurance exercise, oxygen consumption increases which will cause disturbance in intracellular pro-oxidant-antioxidant homeostasis [64]. Modulations of oxidative and nitrative stress can control tissue damage, bacterial translocation and intestinal permeability. Enzymatic and nonenzymatic antioxidant protect excessive oxidative damage, and therefore, consumption of antioxidant would be a beneficial to control the oxidative damage [65]. The relationship between gut microbiota and controlling GI redox is still not clear. Some data found that *Lactobacillus* and *Bifidobacterium* levels are negatively correlated with oxidative stress, while the *Escherichia coli* population is positively correlated with oxidative stress [66]. Study in mice, found that higher levels of *Bacteroidetes* protect against intestinal infection by supressing pro-inflammatory and pro-oxidant responses [67].

#### **3.4 Dehydration status**

During endurance exercise, an increased in fluid loss from sweating will lead to dehydration [68]. One of the main functions of mucosal epithelial cells is transportation of electrolyte. For proper functioning and protection of intestinal barrier, proper water transport and mucosal hydration are necessary [69]. During excessive exercise, studies found that healthy gut microbiota can maintain proper hydration and will prevent inflammatory response. Evidence suggest that activation of Cl- secretion alters the colonic inner mucus layer which lead to the increased in abundance of *Firmicutes* phylum and *Alistipes* genera [70]. In order to obtain a good hydration state and protect intestinal barrier in athletes, it became necessary to understand the role gut microbiota on water transport, diet and mucus intestinal layer.
