**2. Gut Microbiota**

Gut microbiota refers to specific microbial population in the gut that includes the bacterial and viral origin and is considered as non-pathogenic [12]. Gut microbiota coordinately works with the immune system of the host, to protect from pathogen colonization and invasion. Gut microbiota act as a good source of essential nutrients and vitamins, also help in the extraction of nutrients, including vitamins and SCFA from food. In the end, host depends on its intestinal microbiota, and intestinal microbiota contribute to the host's health [13]. The interplay between gut microbiota and host physiology influences the metabolic phenotype, stress response of the host. Further, the equilibrium between the microbial diversity is is essential maintain the host homeostasis including energy metabolism, oxidative stress, hydration status, immunity response, systematic inflammatory response and brain-gut axis [14]. The dysbiosis in the gut microbiota may contribute to the onset of chronic conditions including inflammatory and irritable bowel diseases, gastrointestinal symptoms linked to exercise, colorectal cancer, obesity, diabetes, metabolic syndrome, allergy, depression, anxiety [15]. The factors that influence host intestinal microbiota are genetic, lifestyle including physical activities, diet and environmental factor [9]. Physical activity is linked to specific markers of intestinal health [16–18]. Some of the evidence suggests that exercise positively influence the gut microbial community, which is beneficial to the host [19].

#### **2.1 Effect of diet on gut microbiota**

The human diet is very complex, where foods are not consumed separately, and nutrients are act synergistically. Hence, the dietary patterns are considered the key element of human health. Dietary habits includes the diet variety, nutrient adequacy, intake of healthy food, and considerable amount of less healthy foods [15, 20]. Changes in dietary habits leads to change in the GM. GM since diet has a significant role in determining the composition of GM [21, 22]. Alternative or mismanagement in dietary patterns may harm the population of healthy microorganisms in GM. Researchers have identified that prevailing dietary patterns in US, European and Asian populations, may have a risk of diabetes and obesity [23, 24]. *Bifidobacteria*, *Clostridium* and *Bacteroidetes* decreases due to low carbohydrate diet as carbohydrate is the source of energy for these microbes [25, 26] studies have found that intake of dietary fiber in the diet increases the short chain fatty acid (SCFA) producing bacteria in the GM. The western diet rich in animal protein and fat showed a significant

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

reduction in gut microbiota diversity due to the low amount of dietary fibers [27]. The mediterranean diet includes intake of various polyphenol rich fruits, herbs and vegetables which lower down the risk of metabolic diseases especially diabetes and obesity [28]. Intake of a high protein diet leads to increased *Bacteroidetes*, *Lactobacillus*, *Bifidobacteria* which will benefit the host for metabolism, immune system and nervous system [29]. Keto diet will lead to Dysmicrobism because microbiota need carbohydrates as a source of energy [30]. Intake of high-fat diet will result in impairments in colonic epithelial integrity and barrier function due to the decrease in *Bacteroidetes* and *Firmicutes* [31].

#### **2.2 Effect of endurance performance on gut microbiota**

The effect of excessive exercise on human gut microbiota compositions depends on several factors like body fat, age, diet, timing, training status of the particular subjects. Effect of exercise start early in life. Physical activities promote increases in *Bacteroidetes* and decreases in the *Firmicutes* phylum in the gut of young than in adults, also increases in lean body mass through the adaptation of host metabolism [32, 33]. Several have reported that microbial population altered by exercise favour the development of the brain [9]. Several pieces of evidence reveal the present of diverse microflora in an athlete, with an abundance of *Bacteroidetes, Akkermansia, Veillonellaceae, Prevotella,* and *Methanobevibacter* [32]. A higher amount of *Prevotella* and *Methanobrevibacter smithii* were found in professional as compared to amateur cyclists. This microflora is known to involve in carbohydrate and energy metabolism in the human body [34, 35]. Overweight adults, following a fiber and whole-grainrich diet for six weeks, the presence of *Prevotella* abundance predictive of weight loss, suggesting that enterotype should be considered in personalized nutritional strategies to counteract obesity [36, 37]. One of the studies shows the difference of microflora between active and sedentary Women. Active women have a higher amount of health-promoting bacterial species, including *Akkermansia muciniphila, Roseburia hominis, Faecalibacterium prausnitzii* and *Coprococcus* genus [38, 39]. *Akkermansia muciniphila* is a mucin degrading bacteria that protects the intestinal lumen, and its levels are, negatively associated with metabolic disorder in pateints with inflammatory bowel diseases [40, 41]. In addition, exercise has shown positive impact on the gut mucus layer, which is an essential substrate for the mucosa-associated bacteria e.g. *Akkermansia muciniphila. Roseburia hominis* and *Faecalibacterium prausnitzii* were known to produce butyrate, showing a positive impact on intestinal function and metabolism of lipid, thereby having anti-inflammatory properties [42]. Other studies have also reported the abundance of *Coprococcus* genus in active women [32]. One of the study conducted between lean and obese adults performing endurance exercise under proper dietary control reveal the abundance of butyrate producing taxa in lean adults as compared to the obese adults [43]. Similar studies reported by Galle, (2019), showed the abundant of *Faecalibacterium* sp. in lean adults compared to obese adults [44]. This study confirmed the influence of BMI in gut microbiota. Thereby normalizing the BMI, age and diet can have a beneficial effect on individuals, by increasing butyrate producing taxa.

Recently, it was reported that *Veillonella* is a performance enhancing microbe known to utilize lactate and produce propionate [45]*.* Similar studies reported that lactate can be converted into propionate by the *Veillonella* [46]. Thus the production of SCFA by gut microbiota will promote health benefits toward the host during exercise, thereby contributing to exercise-induced adaptation. The SCFA produce by the microbiota fermentation will later act as an energy source for the liver and muscle cells, thereby improving endurance performance. Moreover, it is needed to balance the gut microbiota composition over time.
