The+Powers+of+Your+Gut+Microbiome

toc =** Introduction **=

The human gastrointestinal (GI) tract encompasses a dynamic community of organisms called the gut microbiota. The digestive tract itself is a “center point of the central nervous system, hormonal system and immune system” [19]. These microorganisms in the gut play a vital role in our bodies and in our day to day lives by obtaining the responsibility of controlling a balance of our emotions and bacteria, which may contribute to diseases. The amount of microbes that inhabit the GI tract has been estimated to be greater than 10^14 [2,18]. This encompasses up to 100 times more bacterial cells than the amount of genomic content as the human genome [12]. Due to the large number of bacterial cells in the body, the host and the microorganisms inhabiting it have the greatest density of bacteria found in the body. As a result of this, it is often referred to as a ‘superprganism’ [11,12]. Yet, 70 million people from across the world suffer from some sort of digestive issue and know minimal about the roles and interactions the GI tract has with the rest of the body [11]. This suggests the necessity of understanding the development and composition of the human GI microbiota, and its need for mechanistic studies that focus on the interactions between the gut and the rest of the body.

=** Roles of the Gut **=

In recent years, the gut microbiome has become a relevant topic amongst doctors and researchers. Its significance and roles in the biology and development of humans has been proven worldwide as more research is being done on the human microbiota. Researchers learned the gut microbiota and the host have "co-evolved over thousands of years to form a mutually beneficial relationship, which is pivotal in maintaining homeostasis" [2,22]. There has a been a lot of speculation about how exactly the gut microbiome and the host immune system influence each other during certain diseases, but a function for the microbiota in a vast number of diseases has become steadily evident.

Because of the increased rate in research about the gut microbiome, it has been acknowledged the microorganisms that make up the gut microbiota have crucial impacts on the host during homeostasis and certain diseases [1]. Some benefits of the microbiota include protecting against pathogens [3], regulating host immunity [12], and saving energy [7]. However, there is potential for these mechanisms to be disrupted as a result of an imbalance of microbial composition, known as dysbiosis.

One of the main roles of the gut microbiome is to prevent a dysbiosis from occurring. When an imbalance of bacteria occurs, it has the potential to disturb the host and thus the rest of the body. Intestinal bacteria play a substantial role in maintaining immune and metabolic homeostasis and protecting against pathogens. Studies have linked the pathogenesis of many diseases and infections with “altered gut bacterial composition (dysbiosis)” [25]. Therefore, the urgency of understanding what causes a dysbiosis in the gut microbiome is imperative to understand a person’s health.

=** What Effects the Gut Microbiome **=

It is critical to know how to “keep the collection of bacteria, archaea and eukarya colonizing the GI tract at a balance” [2,25]. There are several factors that contribute to the fundamental structure of the human microbiota. One of the most compelling elements in shaping the gut microbiota is diet [15]. An individual’s diet is considered to be one of the cores in shaping the gut microbiota across a lifetime, starting from birth [25]. Current research suggests that "diet exerts a large effect on the gut microbiota" [5]. For instance, a high-fat-diet induces alterations in the gut microbiota, which can lead to obesity and chronic disease risk [15]. Another important factor that plays a role in the establishment of the gut microbiome is stress. Research has shown that stress can directly affect the live bacteria in your gut. The brain and the GI tract are bidirectionally linked in a way that can be seen as what researchers call the gut-brain axis [14]. The microbiota has emerged into a key player in the control of the gut-brain axis. The gut microbiota has been implicated in a variety of stress-related conditions which include anxiety, depression and irritable bowel syndrome [14].

Although there are factors that negatively affect the gut microbiome, there are factors that will positively affect it. Two of the most beneficial influences include prebiotics and probiotics [8]. “Several studies have shown that diets that modify the microbiota with prebiotics, and probiotics can reduce stress-related behavior” [9]. =** Research **=

Research on the microbiome is considered to be an emerging science. However, in recent years, scientists have made astounding progress in understanding the microbes that make up the gut microbiome, and its association with human disease. Researchers are understanding more how the microbiome impacts human health. They have found that the two main factors that lead to gut microbiome dysbiosis and disturbance of the gut are stress and diet [20]. Nonetheless, the emerging literature implicates diet as the most important influence on the microbial in the gut [28]. Consequentially, the lack of proper nutrition has been linked to disturbances in the microbiota.

Since much of the impact on the gut microbiome is mediated through diet, Turbnaugh and colleagues “conducted an extensive set of diet shift comparisons using a “humanized mouse model” [20]. The mouse was fed a “western” diet, which is high in fat and fed another mouse a fat restricting diet. What they observed in only a single day was an evident effect of diet shift on the gut microbiome. They reported that a high-fat-diet promotes a decrease in //Bacteroidetes// and an increase in both //Firmicutes// and //Proteobacteria// [9,21]. Inside the gut microbial, most of the species belong to four phyla: //Firmicutes, Proteobacteria, Bacteroidetes,// and //Actinobactera [11].// Changes in the ratio of //Firmicutes// and //Bacteroidetes// correlates with obesity. The results from this research suggests that a high-fat-diet promotes an increase of //Firmicutes// and //Protebactera// and a decrease of //Bacteroidetes.// The quick shift in dominating bacteria promotes a more effective caloric intake which leads to obesity [14,15]. Likewise, when an individual is obese and shifts to a fat-restricted diet, his or her body weight decreases and there is an increase of //Bacteroidetes// [14].

Evidence for a crucial role for the microbiota in regulating stress-related changes in brain function and physiology has emerged from animal studies. In 2004, a discovery was made when conducting a study on germ-free mice. The mice were found to have exaggerated HPA axis when responding to stress, which could be reversed by colonization with a bacterium species called //Bifidobacteria// [23]. //Bifidobacterium// is one of the major bacteria located in the colon flora in mammals, and can be used as a probiotic [24]. When the HPA axis is activated, an increase in cortisol levels is secreted into the blood. High levels of the cortisol hormone disturb the balance of bacteria in the gut, so the addition of //Bifidobacterium// is necessary in order to lower the levels of cortisol. The results from this study support the connection between gut microbiota and response to stress.

Studies have shown a definitive association between prebiotics, probiotics and the gut microbiota. For example, there has been a reduction of anxiety and depressive-like behaviors in socially isolated mice by the use of a dietary supplement that contains the probiotic strand //Lactobacillus rhamnosus// [9]. The addition of a probiotic in this research balanced the dysbiosis of bacteria in the gut microbiome. In addition, the behavior effects were correlated with changes in composition in the microbiota. This suggests that there are protective effects mediated by the microbiota on the brain.

In another study of the effects of probiotic on the gut microbiome, human studies paralleled with the mice findings. A research team in France constructed a “double-blinded, placebo-controlled, randomized parallel group study” that gave the human studies strains of //Lactobacillus// and //Bifidobacterium// for 30 days [19]. By the end of the study, the results “yielded beneficial psychological effects” included a lower rate of depression, less anxiety and anger when compared to the group that received the placebo [19].

=** Conclusion **=

The relationship between the host and the gut microbiome can be expressed as a symbiotic relationship. This symbiotic relationship can also be seen between the brain and the gut—termed as the brain-gut axis. Therefore, it is not astonishing to discover a disruption in normal microbiota composition when the body is in a diseased state. Studying microorganism molecules that affect our day-to-day lives has advanced our understanding of the “mechanisms linking the gut microbiota composition and its activity to health and disease phenotypes” [2].

In our findings, it is evident that diet is one of the most modifying factors of the gut microbiota. Diet is also A person’s diet has the capability to benefit or harm the balance of bacteria in the gut. When an imbalance of bacteria happens, the dysbiotic microbiota “might be unsuccessful to provide the host with the complement of beneficial properties” [2, 6]. Thus, it is crucial the gut microbiota is taken care of with proper nutrition (i.e. a diet not high in fat and sugars) in order to be in harmony with the host. Acquiring good bacteria is essential for having healthy digestion. Studies have documented the beneficial effects of probiotics and prebiotics in healthy individuals. Incorporating your diet with more prebiotics and probiotics is essential for long term health, i.e. aiding helping with digestion and balancing hormones. Eating prebiotics and/or probiotics can be done in supplement form or food such as sauerkraut, yogurt, fermented milk, and kimchi [4]. It is suggested that a quality supplement contains the bacteria strains //Lactobacillus// and //Bifidobacterium//. Overall, maintaining a healthy gut is achievable through diet and prebiotics/probiotics.

=** References **=

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