on June 26, 2026
An invisible ecosystem that accompanies us throughout life
The human body is home to trillions of microorganisms distributed across different body sites. The gut, oral cavity, skin, respiratory tract, and vaginal mucosa are dynamic environments in which bacteria, archaea, viruses, and fungi coexist with the host in a relationship of continuous mutual regulation.
This community is known as the microbiota.
The term microbiome refers to the overall genetic heritage expressed by the microorganisms that make up the microbiota.
This distinction is not merely terminological.
The microbiota represents the collection of living organisms, while the microbiome describes their functional and metabolic potential.
Humans do not live apart from their microbiota but in a state of biological interdependence that is often described as mutualism.
Under balanced conditions, known as eubiosis, the microbial composition contributes to the maintenance of homeostasis.
When, however, alterations are observed in the diversity, stability, or function of microbial communities, this is referred to as dysbiosis.
Dysbiosis is not a disease but a biological condition associated in various contexts with functional changes in the host.
Gut microbiota: a metabolic and immunological platform
The gut hosts the largest proportion of the human microbiota by quantity.
This microbial population participates in numerous physiological functions.
These include the fermentation of dietary fiber, production of bioactive metabolites, regulation of intestinal permeability, interaction with the immune system, participation in bile acid metabolism, and support of digestion.
Among the most studied metabolites are short-chain fatty acids, known as SCFAs, which are produced mainly through fiber fermentation.
Acetate, propionate, and butyrate are involved in the maintenance of the intestinal epithelium, immune communication, and energy regulation.
The microbial balance can be influenced by diet, stress, medications, infections, surgery, age, physical activity, and lifestyle.
Dietary fiber: nourishment for the intestinal ecosystem
Fiber is one of the most studied nutritional tools for supporting the microbiota.
Dietary fibers are not completely digested by humans but become a metabolic substrate for specific groups of microorganisms.
This process can promote the production of metabolites involved in intestinal balance.
From a functional standpoint, fiber can help hydrate the stool in conditions characterized by constipation while simultaneously increasing the consistency and structure of the intestinal contents in certain conditions characterized by increased fluidity.
Foods naturally rich in prebiotic components include chicory, artichokes, asparagus, oats, wheat, soy, bananas, onions, garlic, leeks, legumes, and certain plant matrices rich in inulin and fructooligosaccharides.
Probiotics and prebiotics: when microorganisms become functional nutrition
Probiotics are defined as live microorganisms that, when taken in an adequate amount, confer a health benefit to the host.
Not all probiotics are the same.
The observed effects depend on the strain used, the dose, viability, and the physiological context.
Among the most studied genera are Lactobacillus, Bifidobacterium, Bacillus, and selected strains from other microbial genera.
Fermented foods are a dietary source of microorganisms and include yogurt, kefir, sauerkraut, kombucha, certain fermented cheeses, and unpasteurized plant-based preparations.
The effects of probiotics may be enhanced by the concurrent intake of prebiotics, substances selectively utilized by beneficial microorganisms.
Algae and microbiota: a new nutritional frontier
In recent years, interest in microalgae and marine compounds has increased.
Species such as Chlorella and Spirulina are studied for their protein, pigment, polysaccharide, vitamin, and antioxidant compound content.
Phycocyanin found in spirulina has been investigated for biological activities related to the modulation of oxidative stress and the inflammatory response.
Some preclinical studies also suggest possible effects on the intestinal microbial profile and the selection of bacterial populations associated with eubiosis.
However, much of the evidence still comes from experimental studies and requires further clinical confirmation.
The gut–brain axis: continuous communication
One of the most active areas of contemporary research concerns the so-called gut–brain axis.
The central nervous system, enteric nervous system, microbiota, and immune system form a bidirectional communication network.
The microbiota can influence the brain through microbial metabolites, neuroendocrine pathways, immune regulation, and vagal signals.
The enteric nervous system coordinates motility, secretion, blood flow, and digestive function.
Serotonin is one of the main mediators involved in this communication.
A significant portion of the body's serotonin is produced in the gut, where it contributes to the regulation of motility and enteric function.
Psychobiotic research studies probiotic strains selected for their potential impact on the gut–brain axis and neurofunctional well-being.
To date, the evidence is promising but still evolving and does not yet support the use of psychobiotics as a treatment for neurological or psychiatric disorders.
Microbiota and skin: the gut–skin axis dialogue
The gut and skin share common immune and metabolic mechanisms.
In recent years, the concept of the gut–skin axis has gained increasing attention.
Some studies suggest that maintaining microbial balance may influence parameters related to the skin barrier, hydration, and inflammatory response.
Probiotics have been studied for their potential role in modulating ceramide production, regulating barrier function, and reducing transepidermal water loss.
A randomized clinical study conducted with Lactobacillus plantarum HY7714 showed improvements in hydration and certain skin parameters after oral supplementation.
Other experimental work has observed interactions with collagen metabolism, response to UV rays, and metalloproteinase activity.
These results are promising but do not replace traditional dermatological approaches.
Microbiota, photoaging, and biological skin protection
Photoaging is the result of chronic exposure to ultraviolet radiation.
UV radiation increases the production of free radicals, alters collagen and elastin, and influences the skin's inflammatory response.
Some probiotic strains have been studied for their potential role in supporting the skin barrier and modulating oxidative stress.
Scientific interest focuses primarily on the ability to indirectly support the balance of the skin environment through gut–skin communication.
Sun protection, however, remains the main validated tool for preventing photoinduced damage.
Bibliography
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Cryan JF et al. The Microbiota-Gut-Brain Axis. Physiol Rev. 2019.
Hill C et al. Expert consensus document: Probiotics definition and scope. Nat Rev Gastroenterol Hepatol. 2014.
Makki K et al. The Impact of Dietary Fiber on Gut Microbiota. Cell Host Microbe. 2018.
Rinninella E et al. What is the Healthy Gut Microbiota Composition? Microorganisms. 2019.
Ogawa M et al. Oral administration of Lactobacillus and skin barrier function.
Kim HM et al. Oral Lactobacillus plantarum HY7714 improves skin hydration and elasticity. J Microbiol Biotechnol.
Salem I et al. Microbiome and dermatology. Front Cell Infect Microbiol. 2018.
Sarkar A et al. Psychobiotics and the gut-brain axis. Trends Neurosci. 2016.
Marco ML et al. Health benefits of fermented foods. Nat Rev Gastroenterol Hepatol. 2021.
Plaza M et al. Marine microalgae and human health applications. Trends Food Sci Technol.
