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Strength in numbers: Building immunity with gut microbiome diversity

“Trusting your gut” gains new meaning with the knowledge that one’s gut microbiome affects every facet of a person’s health.

“You are what you eat” is a common adage used by adults and children alike. It turns out, however, that this casual statement extends further than one might think. It also holds true for the living organisms in humans’ intestines: gut bacteria.

A growing body of evidence is showing that gut bacteria may affect the brain, immune system, susceptibility to disease, and even one’s mental health—emphasizing that one must take the task of regulating gut bacteria more seriously.

From the ground up

Best known for their role in the digestive system, gut bacteria are inherent to one’s small and large intestines. Gut microbiota—the collection of all microorganisms in the gut—is established as soon as one is born, with the majority of its composition coming from the mother.

Dr. Leslie Michelle Dalmacio, a professor at the University of the Philippines Manila’s Department of Biochemistry and Molecular Biology, adds that the bacteria living in the gut may also differ depending on the method of childbirth. For instance, a cesarean child’s microbiota will largely depend on the surrounding environment rather than that of the mother’s gut and vaginal canal.

Gut microbiota develops until age two, with minor changes occurring throughout life due to a person’s diet and physical activity. “Children exposed to the outside environment at early ages have stronger immune systems,” Dalmacio furthers. This is based on the hygiene hypothesis, which explains that immune systems are activated early on because of exposure to various types of bacteria.

Branching from a similar principle, infants fed with a variety of food early in life develop a more diverse set of gut bacteria. “Food may be allergenic due to its components,” Dalmacio states, citing the practice of feeding babies milk and soft foods before gradually introducing them to solid foods.

The slow and careful introduction of these allows the child’s gut microbiome to process the food, leading to gut microbiome development and tolerance to various bacteria. These practices build the foundation for gut bacteria abundance, microbiota composition, and gut microbiota diversity.

While gut bacteria abundance refers to the actual number of certain bacteria in the gut, microbiota composition indicates the constituents, and gut microbiota diversity is the variation of microorganisms present. Among these, however, diversity is what primarily defines one’s gut health and general health.

The body’s metabolic processes are dependent on maintaining a healthy balance of bacteria. For example, the professor posits that a portion of one’s resident flora—the microorganisms which naturally reside in a particular site in the body—is excreted during defecation, but the body naturally replenishes it. “It is also further replenished with dietary intake of probiotics and prebiotics,” she expounds. When a group of gut bacteria dominates the presence of the others, an imbalance called “dysbiosis” occurs.

Unraveling connections

Numerous studies have shown an association between dysbiosis and one’s susceptibility to inflammatory bowel diseases (IBDs), such as ulcerative colitis (UC) and Crohn’s disease (CD)—chronic diseases in the gastrointestinal tract that cannot be cured. Along with greater dysbiosis, patients with CD also have lower gut microbial diversity and a more unstable microbial community compared to those with UC.

Examining microbial signatures, one’s unique bacterial composition resulting from different experiences and environments may identify the role of dysbiosis in the development of IBDs. However, Dalmacio clarifies, “If you get sick, your certain microbial signature will change, but that would not cause the disease.” While scientists have yet to determine the clear link between the two, immune response hints at the larger role of these microbes in one’s overall health.

The gut-brain axis, the communication network that links the gut and the brain, allows these organs to influence both physical and mental health. Metabolic processes within the gut microbiome digest fiber from food, producing short-chain fatty acids that affect brain function, such as regulating nervous system development, mood, and neurotransmitter levels.

In gut endocrine cells, short-chain fatty acids may incite behavioral changes through serotonin production, although its effects have not yet been extensively studied. Since one’s diet affects microbiome metabolism, “we can hypothesize that there will be an association between your gut health and mental health,” Dalmacio surmises.

Routine development

In choosing one’s next meal, having a balanced and varied diet is important. Following regular consumption, fiber and probiotics can be precursors to better gut health.

Incorporating fiber-rich foods into one’s diet can improve “gastrointestinal motility”—the movement of food through the digestive system—and increase good bacteria count to aid in digestion. Probiotics, live good bacteria common in the gut, help maintain gut balance by fighting off bad bacteria from infection. While some probiotics are part of one’s natural flora, Dalmacio warns about ingesting good bacteria from outside sources, “Probiotic supplements will not stay in our intestine for long…but they will work as long as you take them.”

Aside from making a conscious effort to track what one eats, keeping the body in constant motion can also alter the composition of bacteria in the gut, thus, improving function. Exercise can promote the development of butyrate-producing gut bacteria, which can prevent some diseases like IBD and diabetes. Similar to maintaining a diet, individuals must continue exercising for these benefits to take effect.

While listening to one’s gut feelings may provide some clarity to daily experiences, focusing on gut health could be the key to overall well-being. Together with primary treatments, adjunctive therapies in the gut microbiome may be effective against metabolic diseases. With this, maintaining a healthy and varied diet will help improve the diversity of good bacteria in one’s gut.

As the saying goes, “When in doubt, trust your gut.”

By Arianne Joy Melendres

By Francesca Salting

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