While seemingly insignificant and often forgotten, the human microbiome consists of trillions of symbiotic microbial cells that play a critical role in human health, including the digestion of nutrients, elimination of toxins, and regulation of the immune system. In fact, the number of microbes in humans outnumbers the number of human cells! It’s time we gave recognition to the myriad of microscopic organisms facilitating our crucial metabolic processes. 

What is the human microbiome?

The human microbiome is the genetic material of all sorts of microbes, from bacteria to fungi to protozoa, that reside in and on the human body. These microscopic organisms inhabit nearly every part of our body but are especially prominent in the oral and nasal cavities, skin, and gastrointestinal tract. Every one of us has a unique concoction of microbes that we host, resulting in diverse microbial communities amongst different individuals. Due to the uniqueness of each individual’s microbiome, it can serve as an identification factor just like a fingerprint. While microbes are typically associated with disease, the vast majority of the human microbiome coexists in harmony with the human host, providing essential functions that are indispensable for human health and survival. 

What are the functions of the human microbiome?

These hitchhiking microbes that have coevolved with us have left a significant mark on the metabolic pathways that comprise human health. The major functions of the human microbiome include digestion and nutrient absorption, protection from toxins, and regulation of the immune system, among other functions. Let us go through each of these functions.

• Digestion and Nutrient Absorption: The main players of the gut microbiome are bacteria. Specifically, two bacterial phyla, Firmicutes and Bacteroidetes, are present in large proportions in the gut. These gut bacteria, known as gut flora, are capable of producing enzymes that can help us digest polysaccharides, a dietary staple. Additionally, they provide us with beneficial nutrients, including B vitamins (B12, thiamine, riboflavin), vitamin K, and short-chain fatty acids.

• Protection from Toxins: Another type of gut bacteria, Bifidobacteria, is responsible for preventing infections from other bacteria like E. coli by blocking toxins from trespassing the intestinal wall and into the bloodstream.

• Regulation of Immune System: Given that approximately 70-80% of our immune cells reside in the gut, there is an intricate interplay between the immune system and the gut microbiome. The members of the gut microbiota community work together to maintain homeostasis in the immune system. One type of immune cell in the gut, called Gut Associated Lymphoid Tissue (GALT), is responsible for probing the intestinal lining for any foreign substances and activating the immune system. This role could not be performed without the gut microbes, which function to train the GALT to distinguish between harmless bacteria and harmful pathogens to allow for an appropriate response. 

What is some recent research regarding the human microbiome?

• Gut-brain axis: An increasing amount of research studying the role of the gut microbiome in regulating the nervous system, including its link to mental health. There is a continuous, bidirectional communication between the gut microbiota and the brain, where gut microbes are responsible for regulating factors like anxiety, cognition, and mood. In fact, the gut microbiome itself is capable of producing neurotransmitters, like serotonin and dopamine, that exert effects on brain function. It is no wonder why the gut microbiome has often been called the “second brain.” 

• Gut-lung axis and COVID-19: With the gut microbiome’s critical role in regulating the immune system, recent research has indicated that the microbiota can influence our body’s immune response to fighting the respiratory syndrome COVID-19. Studies have shown that an individual’s particular makeup of the gut microbiome can influence the pathogenesis and severity of COVID-19. Individuals with increased proportions of seven classes of gut bacteria, responsible for immune system homeostasis, have been shown to result in less severe COVID-19 cases. 

How can you improve your gut microbiome?

The composition and diversity of the gut microbiome play a critical role in determining health and wellness. Consequently, changes or imbalances in this delicate composition of microbiota can impact human health and contribute to disease. When the normal microbiome ecosystem is perturbed, a condition known as dysbiosis can be correlated to the onset of various conditions, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), obesity, and even cancer. Thus, it is important to explore the lifestyle habits that directly impact the health of the microbiome.

• Diet: The gut is composed of a wide diversity of microbes, which is critical to maintaining homeostasis and providing gut resilience. For instance, with a diverse microbiome, one microbe can fill in for another when a disturbance happens, allowing for a stable state to be reached. Studies have discovered that eating a wide variety of vegetables, fruits, and whole grains can preserve the diversity of gut flora. 

• Physical activity: Exercise is often touted as an important factor in maintaining health. The health of the microbiome is, too, dependent on getting enough physical activity and spending time outdoors. Research suggests that exercise can increase microbiome diversity and enhance the proportion of beneficial microbes, improving health and preventing diseases. 

• Sleep: Being well-rested is another critical factor in maintaining microbiome health. Studies have shown that there is an intricate connection between the microbiome and circadian rhythm, where disruption in either pathway can result in detrimental effects on health. Specifically, it has been shown that disruptions in our circadian rhythm, such as the lack of sleep, can result in consequential changes in the gut microbiome that decrease their ability to regulate metabolic processes, which can disrupt energy metabolism. 

It is quite amazing how these microscopic organisms that make up our human microbiome are capable of a vast range of physiological functions that define human health and disease. Given all that the human microbiome contributes to our day-to-day functioning, it’s important to maintain a varied diet, exercise, and sleep well to allow them to continue serving us!