By Marta Chmielewski (General Member, YCRH), Maddison Mehring, Ashley Aul, and Rachel DuCharme
Executive Summary
The purpose of this scientific blog post is to provide information surrounding the gut microbiome’s role in various aspects of health. Due to a growing interest in the topic, understanding the gut’s impact on the brain, nutrition, and chronic diseases is essential and provides a potential framework for future preventative health promotion work. The body contains many complex biological processes which in the literature are often challenging to understand, written above the standard population reading level, or poorly explained and are therefore unappealing and avoided by most audiences. This provides the opportunity to synthesize complex scientific literature in a way that is easier for reader to understand. The blog aims to inspire future research and inform individuals about the rising importance of gut health.
In the last decade, the gut microbiome, or the community of bacteria that lives in the gut, has captured the attention of researchers and the health community. The microbial community can perform a wide range of metabolic functions in the body to promote health and protect against diseases (Da Silva & Domingues, 2017). Our health depends on the balance of these microbes, which is influenced by the bacteria themselves and what they are fed.
Diet is an important determinant influencing the composition of the gut microbiota. Many studies have shown the relationship between microbiota and adverse health outcomes such as chronic diseases and poor mental health (Clapp et al., 2017; Bhardwaj, 2016).
The human microbiome, like all ecosystems, is in a constant state of change. The connection between these microbes and human health is becoming more evident with evolving research. Understanding the human microbiome may lead to medical discoveries that have the potential to treat and manage many prevalent diseases in the population.
What is the human microbiome?
The human body is home to millions of tiny living organisms known collectively as the human microbiota. Bacteria are microorganisms found on the skin, nose, and mouth but are most prevalent in the gut (Shanahan et al., 2021). These bacteria are acquired during birth and the earliest stages of development and stay with individuals throughout their lifespan. Not having emerged as a field of study until the late 1990s, the human microbiome is now recognized as essential for healthy development, cognitive functioning, immunity, and nutrition (Hair & Sharpe, 2014). Since then, the field of study has been rapidly evolving to understand the role of the human microbiota on health and diseases.
The majority of microbes are symbiotic, meaning they benefit both the human body and the microbiota, while a small number are pathogenic (disease-causing) organisms (Lloyd-Price et al., 2016). Over time, changes in the human microbiota occur due to complex human interactions between the environment, food, animals, and medicine. These interactions have been proven to alter the microbiota composition, potentially influencing adverse health outcomes (Da Silva & Domingues, 2017). The ongoing study of the human microbiome highlights the role of a healthy gut in the prevention and management of diseases. Could the diversity of microorganisms that live inside and, on our bodies, change the future of human health?
Breaking down gut health
(1) Brain-Gut Connection
Proper functioning of a healthy gut has been shown to positively impact the central nervous system (CNS) because of our gut's connection with our brain (Clapp et al., 2017; Zhou & Foster, 2015). The connection between our gut and brain leaves many people curious about how the interaction works. Researchers refer to this bidirectional relationship as the gut-brain axis (GBA) which links our central and enteric nervous system (ENS) (Appleton, 2018; Sudo et al., 2004). Others have referred to the ENS as the "brain in your gut" due to its ability to communicate with the CNS, impacting our mood, cognition and even mental health (Appleton, 2018; Pasricha, n.d.).
The GBA connects the CNS to the gut microbiota, whereby the gut sends signals to our brain through autonomic neurons and vice versa (Appleton, 2018; Clapp et al., 2017; Foster et al., 2013). Disruption to the gut, such as inflammation or an imbalance of gut bacteria (dysbiosis), has been linked to mental illness (Clapp et al., 2017; Harvard Health, 2021). Researchers have found depressive disorders caused by imbalances in proteins responsible for regulating inflammation, which interferes with our brain functioning and increases stress on the microbiome (Clapp et al., 2017). These proteins enter a barrier accountable for protecting the brain from toxins causing our immune system to fight the body leading to depressive symptoms (Appleton, 2018; Clapp et al., 2017).
Mood changes can be triggered by signals sent to the CNS caused by irritation in the gastrointestinal (GI) system, which may explain why individuals living with GI disruptions are at an increased risk of developing mental illnesses (Appleton, 2018; Pasricha, n.d.). Probiotics have been shown to restore microbial levels, reducing the risk of mental illness similar to conventional treatments (Clapp et al., 2017; Robertson, 2020). However, despite supporting evidence to prevent and treat depressive disorders, further research is required to understand the GBA relationship in humans.
(2) Nutrition & Diet
Diet and nutrition can shape our gut’s microbiome environment by increasing or decreasing the number of beneficial bacteria (Singh et al., 2017). Our intestinal microbiota is responsible for synthesizing amino acids and vitamins to regulate our metabolism and to build up our immune system (Martinez et al., 2021). Intestinal microbiota also plays a role in the absorption, digestion, and storage of vitamins and nutrients in the gut (Martinez et al., 2021). Regular day-to-day variations in our food intake can cause shifts in the microbiota composition (Singh et al., 2017).
Western diets today that include highly processed foods that contain fat, sugar, starches, and oil disrupt the metabolic process and behaviours of the gut (Zinöcker & Lindseth, 2018). Highly processed foods, including french fries, candy, pop or chips, can lead to permanent changes in our microbiota diversity, depleting the bacteria responsible for regulation and microbiome function. Our daily dietary intake of these processed foods provides a lower quality of gut bacteria and nutrients required in the long term (Zinöcker & Lindseth, 2018). Regularly eating out at fast-food restaurants can put us at a higher risk for developing gut-related diseases (Zinöcker & Lindseth, 2018).
Dietary patterns have been shown to impact our gut’s microbiota positively and negatively and thus our health and wellbeing. Popular dietary trends and fads can modify the microbiota differently based on our environmental factors and individualistic microbial profile that we all start with (Hills et al., 2019). For example, a study by De Koning shows that ketogenic diets that restrict carbohydrates to rely on ketone bodies for energy rather than glucose reduce the fibre and prebiotics necessary for bacteria diversity (De Koning, 2011, as cited in Hills et al., 2019). Comparatively, intermittent fasting is another popular diet fad many have tried by restricting eating during specific periods of the day. Interestingly, Hills et al. (2019) found that restricting eating times to an eight-hour window during the day improves gut function and increases the number of diverse bacteria found in our microbiota. A vital takeaway to note is that regardless of the diet followed, the quality and diversity of bacteria in our gut are essential to our gut health. (García-Montero et al., 2021).
(3) Diseases and Disorders
Changes in the gut microbiome brought about by diet and other factors can lead to the onset of certain diseases and disorders. Research has come out lately linking the two together (Bhardwaj, 2016). The GI flora plays an essential role in health and many pathological disorders such as cancer, multisystem organ failure, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), colitis, celiac disease, and in allergies, obesity, and type 2 diabetes mellitus, among many others (Biswas & Rahaman, 2020).
Two of the most common intestinal disorders are IBD and IBS. These chronic conditions manifest as abdominal pains and urgent bowel movements (Biswas & Rahaman, 2020). Even though they have similar symptoms, they are unique conditions. IBS is a condition of the GI tract, with no abnormalities visualized on a colon exam. In contrast, IBD is inflammation or damage of the bowel walls, possibly causing sores and tightening the intestines, and there are two main types called ulcerative colitis and Crohn’s disease. A study by Biswas and Rahaman (2020) found that causes of both include a history of enteric infection, changes in the brain-gut connection, immune system malfunction, and is chiefly linked to changes in the gut microflora. This altered flora can prompt changes in gut permeability, motility, and food processing leading to chronic disease symptoms. Another grouping of studies by Pittayanon et al. (2019) reveals that varying types of microbiotas may affect the host through immune–microbial connections and therefore affect symptoms. The authors confirmed a list of possible harmful microbiota in IBS patients and their multiple pathogenic bacteria. A consistent finding across studies was a likely protective bacterial group in IBS patients associated with preserving the health of gut mucosa, working as an anti-inflammatory organism, and upholding the integrity of the gut–barrier. Currently, there is an absence of consistency between the results of different studies (Pittayanon et al., 2019).
A healthy gut microflora aids in preserving the intestinal barrier function, preventing inflammation, training the immune system, and manufacturing hormones and vitamins (Bhardwaj, 2016; Zinöcker & Lindseth, 2018). The intricate collaboration between the host immunity, the host’s gut microbiota, and the pathogen can trigger enteric infections caused by ingesting food or water contaminated with microorganisms and toxins that attack the GI tract (Biswas & Rahaman, 2020). Interestingly, the gut microbiota can promote acute enteric infections that modify the gut environment, stimulating chronic conditions such as diabetes, leaky gut syndrome or obesity. Overall, the microbiome maintains a critical role, whether permanent or transient, in the host’s gut, creating a large share of the ecosystem. Nevertheless, researchers are far from completely understanding the microbiome’s extensive role in health and the range of complications possible from interruptions in the microbiome-host interactions (Biswas & Rahaman, 2020).
The future of gut health
The microbiome plays a significant role in the human body, specifically physical and mental wellbeing. In addition to medical disciplines like pharmacology, nutrition and dietetics, public health also calls for studying changes in the gut microbiome. By understanding the complex relationship between the gut and health outcomes we can learn about the health and wellbeing of individuals and communities. The future of health promotion begins with trusting your gut!
References
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