Gut Microbiota: The Recipe for Butterflies in the Stomach

The lion’s share of our microbiome is concentrated in our gut - where it is warm, cozy, and constantly supplied with fresh tasty food. Heaven on earth. The surface area of our digestive tract is estimated to be spans 250-400 m², which is two orders of magnitude larger than the surface area of our skin. In fact, this entire area is covered by a biofilm of microorganisms and serves as a vast interface for interaction between our body and microbes. For a long time, it was believed (and this view is still occasionally encountered) that the number of microbial cells inhabiting our body was ten times greater than the number of our own cells. More recent estimates suggest that this ratio is smaller - closer to 3:1 or even 1:1. The highest microbial density is found in the colon: one gram of its contents contains up to 10¹² microbes.

Studying this entire microbial fraternity is complicated by the fact that most of its members are unable to live on their own in laboratory test tubes. They urgently need company to carry out the intricate biochemical transformations they perform when they are “in the wild.”

However, with the dawn of the genomic era, scientists have begun to lift the curtain on the microbial diversity within us. We now know that our bodies are home not only to familiar inhabitants such as Escherichia coli, lactobacilli, and bifidobacteria, but also to thousands of other microbial species.

What do they all do there?

The microbes in our gut truly protect us from foreign invaders, though they do so less out of affection for us and more to defend their own ecological niche in the struggle for survival.

Nevertheless, gut microorganisms diligently pay rent for their living space - for example, by synthesizing B vitamins, vitamin K, and folic acid. Moreover, if we remember to eat fiber-rich foods, this list expands to include short-chain fatty acids (SCFAs).

These molecules are especially important because they serve as a primary energy source for the epithelial cells lining the intestines, helping to maintain the integrity and health of the gut barrier. Short-chain fatty acids regulate the activity of regulatory T cells and diminish the development of inflammatory processes in the gut. In addition, these metabolites interact with enteroendocrine cells - intestinal cells capable of producing hormones - and stimulate the release of a wide range of peptides, neurotransmitters, and hormones, including serotonin and oxytocin.

Lately, it has become fashionable to say that the gut microbiota influences our mood - and as we’ve seen, such claims are not unfounded. In fact, researchers are already exploring the role of gut microbes in the development of conditions such as depression, schizophrenia, bipolar disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. While it is not yet possible to pinpoint specific pathogens, studies suggest subtle correlations between certain microbial groups and the emergence of these conditions, with particular attention to the abundance of bacteria such as Clostridia, Desulfovibrio, Bacteroides, and members of the Lachnospiraceae family.

Studies of gnotobiotes (laboratory animals raised in completely sterile conditions) show that the gut microbiota plays a crucial role in forming the blood–brain barrier (the protective shield that prevents microbes from invading the brain), in regulating neuronal myelination (the process by which the myelin sheath insulates neurons and ensures proper electrical signaling), and in neurogenesis (the development of new neurons).

It should also be highlighted that the neurotransmitter gamma-aminobutyric acid (GABA) can be synthesized by certain strains of Lactobacillus, Bifidobacterium, and Bacteroides. Beyond its potential role in reducing vulnerability to depression, GABA is also involved in the local regulation of inflammatory responses.

Another global function of the gut microbiota is the training of the immune system. During the early years of life, exposure to a diverse range of microbes appears to calibrate immune responses, enabling the immune system to react appropriately to antigens and to distinguish between harmless and harmful stimuli. Insufficient microbial exposure during this critical period is associated with an increased risk of developing allergic diseases later in life.

How to maintain your gut zen?

• Consume fiber-rich foods such as vegetables, fruits, and whole-grain products. At the same time, it is advisable to avoid excessive thermal processing - overcooked vegetables that fall apart lose much of their functional fiber. It is also preferable to obtain fiber from whole foods rather than supplements, a choice that reflects both nutritional balance and cost-effectiveness.
• Avoid taking antibiotics without a doctor’s prescription;
• Limit the excessive use of disinfectants and household detergents;
• Consume fermented foods - vegetables, dairy products - they contain beneficial microbiota;
• Spend time in natural environments when possible - contact with non-pathogenic environmental microbes supports immune stimulation and increases microbial diversity.
• And, of course, avoid chronic stress. Prolonged stress elevates pro-inflammatory markers in the blood and can contribute to increased intestinal permeability, commonly referred to as “leaky gut.” This condition reflects a disruption of the intestinal barrier, allowing microorganisms and their metabolic products to penetrate deeper tissues, thereby promoting inflammation and dysbiosis throughout the digestive tract.