The Role of the Gut Microbiota in Health and Disease

Introduction

Did you know that the microbial composition of the gut outnumbers your genes? The human genome contains approximately 23,000 genes, whereas the microbiome encodes over three million genes that produce thousands of metabolites that affect many of our body’s functions, thereby influencing our fitness, phenotype, and health.

The gut microbiota is one of the most interesting and complex systems in the human body. Research into the gut microbiota has been showing that this system is far more important than we ever imagined. This blog will look at how the gut microbiota is involved in your overall health and how we can use this information to change and improve our lives.

The Gut Microbiome and Its Multifarious Functions

A complex network of interactions encompassing the metabolic, immune, and neuroendocrine crosstalk between the gut and your body regulates and stabilises a symbiotic relationship. This crosstalk is potentially mediated by some predominant functions of the gut microbiota and the associated key metabolites that have established a link between the gut and other organ systems, that govern our health and wellness. The most significant functions of the gut are as follows:

Metabolism

The gut microbiota plays an important role in metabolic efficiency and energy harvesting for the human body. It helps in fermenting unabsorbed starch and soluble dietary fibre, resulting in end products in the form of short-chain fatty acids (SCFAs). These end products act as energy substrates for our bodies, thereby contributing an extra 10% of daily dietary energy for utilization for other metabolic processes. Additionally, it has been demonstrated that SCFAs control energy balance by stimulating leptin synthesis, which has a wide range of effects on our physiological processes like appetite, energy metabolism, sympathetic nerve activity, and immunological response. Aside from SCFA, micronutrients synthesized in the gut microbiota, such as vitamins, are beneficial to both microbial and host metabolisms.

Immunity and the Nervous System

The gut barrier is composed of a mucus layer and an epithelial layer that serve as the interface between the outside world and the host’s internal environment. Any disruption to the gut barrier will increase gut permeability to microbes and microbial-derived products, contributing to abnormal immune-inflammatory responses such as inflammation, allergy, and autoimmune disorders.

On the other hand, the emerging modulatory role of gut microbiota in the enteric nervous system (ENS) is widely recognised by researchers. For your information, ENS regulates the physiology and the function of the GI tract and bifacially communicates with the central nervous system (CNS) via vagal pathways, thereby forming the “gut-brain axis.” The malfunctioning of the cells in ENS can result in inflammatory bowel disease (IBD), constipation, Parkinson’s disease, and infection-induced gut inflammation.

Colonisation Resistance

Another important role of the human microbiota is colonisation resistance, wherein the naturally occurring host-microbiota provides protection against the colonisation of pathogenic invaders and prevention against overgrowth of pathogenic microbiota members, called pathobionts.

Effects of Food and Medications on the Gut Microbiota

Our dietary patterns and specific foods influence the abundance of different types of bacteria in the gut, which in turn can affect health. For instance, a recent study has shown that non-nutritive sweetener consumption disrupts the balance and diversity of gut microbiota and alters glycemic responses.

Another source of concern is the impact of popular restrictive diets on gut health. Some strict vegan diets, gluten-free diets, and low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diets are a few examples.

In addition to diet, medications such as antibiotics are a key modulator of the gut microbiota composition. It destroys both pathological and beneficial microbes indiscriminately, resulting in either loss of gut microbiota or growth of unwanted microbes.

Manipulating the Gut Microbiota Through Diet

Changes to the gut microbiota can occur within days of changing a diet. Therefore, by including gut-friendly bacteria in your diet, you may modify the microbial composition of the gut.

Probiotic Food

Probiotics are live micro-organisms, that can boost the host's health by maintaining a healthy balance between pathogens and the bacteria necessary for the normal function of the gut microbiota. Probiotics, which are mostly comprised of Bifidobacterium and Lactobacillus species, can be found in foods such as yoghurt, kefir, kombucha, etc., nutritional supplements, and medications.

Prebiotic Food

Prebiotics are dietary fibres that stimulate the growth and activity of beneficial bacteria in the gastrointestinal tract, which is beneficial for human health. One easy way to start is to simply introduce prebiotic-rich foods into your diet, like bananas, green peas, and kidney beans.

We are entering a time in which we can progressively influence health through food and monitor the outcomes through microbes or metabolites. Fibre is an essential nutrient for a healthy microbiome that has been neglected in the midst of the sugar and fat debates. The negative effects of drugs and processed food ingredients on the microbiome cannot be ignored any further.

The Gut Microbiome and Diseases

External factors such as dietary components, antibiotic consumption, psychological and physical stress, and other environmental factors can impair the normal functioning of the gut microbiome (dysbiosis), which might be harmful to the host, causing a diverse range of diseases. Some of the most commonly discussed are as follows:

Inflammatory Bowel Disease (IBD)

IBD is a group of multifactorial, persistent, and recurring gastrointestinal inflammations. There are two common forms of IBD: Crohn's disease (CD) and ulcerative colitis (UC). In CD, inflammation can occur anywhere along with the whole GIT, whereas UC is only restricted to the large intestine. The interaction of gut microbiota and host factors such as diet, infection, and antibiotic use can result in gut dysbiosis. This reduces the number of beneficial microbiota species, alters gut barrier function, immune response and causes IBD.

Celiac Disease

Celiac disease is a multifactorial, chronic immune-mediated disorder of the small intestine characterised by dietary gluten intolerance. Gut dysbiosis is thought to play a role in the development of Celiac disease. In Celiac patients, there is a significant decrease in "health-promoting" Bifidobacteria species and an increase in virulent gram-negative Bacteroides-Prevotella groups. This may increase inflammation that impairs the gut barrier integrity and normal functioning of the gut. As a result, gluten intolerance and the onset and/or progression of celiac disease are facilitated.

Obesity

Obesity is a global health hazard affecting millions of people worldwide. It is associated with elevated energy intake and decreased energy expenditure, causing excessive fat accumulation with raised body mass index, posing obese individuals to have a higher risk of developing obesity-associated disorders like type-II diabetes, cardiovascular disease, and liver abnormalities. It is observed that elevation of saccharolytic gut bacterial species (Bacteroides thetaiotaomicron) facilitates augmentation in food digestion, leading to higher energy harvest and increased fat deposition, thus contributing to obesity development.

Colorectal Cancer (CRC)

Colorectal cancer (CRC) is the fourth leading cause of cancer-related mortality worldwide. It is a multifaceted disease associated with genetic and environmental factors. According to research, the gut microbiota plays a role in CRC formation, progression, and treatment response. According to one study, the presence of certain bacteria in the gut biome increases the likelihood that colon polyps will become cancerous. Researchers state that a normally healthy gut and its bacteria may adapt in order to survive in an environment with metabolic and inflammatory changes. This adaptation can actually contribute to the inflammation rather than suppress it.

Clostridium Difficile Infection (CDI)

Clostridium difficile is a gram-positive toxin and a spore-producing anaerobe (a bacteria that survives without oxygen). It is also one of the Firmicutes members in the normal gut microbiota. The activity of C. difficile toxins A (TcdA) and B (TcdB) damages the network of cell movement and intestinal barrier integrity. Thereby inducing an abnormal inflammatory response and cell death.

Conclusion

It is now established that the human gut microbiota plays a role in human health and disease. The composition of our gut microbiota can be modified by dietary intervention and supplementation. With the use of beneficial bacteria (probiotics), prebiotics and some simple dietary changes, you can make sure that you are taking the best care of your gut microbiota possible.