What Is Dysbiosis and When Does It Have Clinical Significance?

The human body hosts complex communities of microorganisms, including mainly bacteria, as well as fungi, viruses, and other microorganisms. The collection of these microorganisms in a specific area of the body is known as the microbiome. The gut microbiome is of particular scientific and clinical interest because it is involved in numerous functions related to digestion, metabolism, immune responses, and maintenance of the intestinal barrier.

Dysbiosis describes changes in the composition and/or function of a microbial community that deviate from a functionally balanced microbial ecosystem. In the gut, these changes may involve the relative abundance of specific microorganisms, microbial diversity, interactions among microorganisms, or the metabolic functions they perform.

Dysbiosis, however, does not in itself constitute a specific disease or diagnosis. No single “normal” gut microbiome is common to all individuals. Microbiome composition varies considerably among healthy individuals and is influenced by numerous factors, including age, diet, lifestyle, geographical location, medication use, and the broader environment.

For this reason, detecting a difference in microbial composition does not necessarily indicate a pathological condition. The clinical significance of dysbiosis depends on the type and extent of the changes, their functional impact, and, most importantly, whether they are accompanied by symptoms or other laboratory and clinical findings.

Therefore, the modern approach is not limited to the question of “which bacteria are present in the gut,” but more broadly considers the function of the intestinal ecosystem and its relationship to an individual’s health status.

How and Why Can Dysbiosis Develop?

The gut microbiome is a dynamic ecosystem that changes continuously in response to environmental factors and factors related to the individual organism. Some changes are normal and transient, while others may be more pronounced or persist longer, affecting the function of the intestinal ecosystem.

Dysbiosis is generally not attributed to a single factor. More commonly, it results from interactions among dietary, environmental, pharmacological, and biological factors. Factors that can significantly influence the gut microbiome include:

Diet. The amount and type of dietary fiber, the diversity of plant foods, and the overall composition of the diet influence substrate availability for gut bacteria and the production of microbial metabolites.
Antibiotics and other medications. Antibiotics can significantly change the composition and diversity of the microbiome. Other classes of medications may also have an effect, depending on the type and duration of treatment.
Gastrointestinal infections. Acute gastroenteritis can disrupt the gut microbial community temporarily or, in some cases, for a longer period.
Age and physiological changes. The microbiome changes considerably from infancy through adulthood and continues to evolve with aging. Therefore, some differences in its composition are part of normal biological variation.
Lifestyle and environment. Physical activity, sleep, chronic stress, dietary habits, and various environmental exposures can directly or indirectly influence the intestinal ecosystem.
Underlying diseases and metabolic disorders. Microbiome alterations are observed in many pathological conditions. In these cases, however, the relationship may be bidirectional: disease can affect the microbiome, while changes in the microbiome may, in turn, contribute to certain pathophysiological mechanisms.

An important characteristic of the gut microbiome is its resilience, meaning its ability to return toward its previous functional state following a disturbance. For example, a short term dietary change or an acute infection may temporarily alter microbial composition without necessarily resulting in persistent dysfunction.

For this reason, dysbiosis should not simply be viewed as the presence of “good” or “bad” bacteria. More important is the extent to which these changes affect the overall function of the ecosystem, the production of important microbial metabolites, the integrity of the intestinal barrier, and interactions between the microbiome and the host.

When Does Dysbiosis Become Clinically Significant?

Differences in gut microbiome composition do not necessarily indicate a health problem. The key question is whether these changes are accompanied by impaired intestinal ecosystem function and whether they are associated with the individual’s clinical presentation.

Dysbiosis becomes more clinically significant when microbial findings are accompanied by persistent symptoms, functional changes, or other objective markers. In other words, microbiome analysis results should not be interpreted in isolation.

Possible associated symptoms
Investigation may be particularly relevant when persistent or recurrent gastrointestinal symptoms are present, such as:

abdominal pain or discomfort
flatulence and pronounced bloating
diarrhea or frequent changes in bowel movements
constipation
changes in stool consistency

These symptoms are non-specific and can occur in many different conditions. Therefore, their presence does not confirm dysbiosis, nor does it necessarily mean that the microbiome is the cause. They should be evaluated within the context of the overall clinical picture.

Complementary markers of the intestinal environment
The functional significance of a microbiome alteration can be assessed more comprehensively when parameters related to the intestinal environment are evaluated alongside it.

For example, short-chain fatty acid (SCFA) production is an important function of the microbiome. Metabolites such as butyrate, acetate, and propionate are produced primarily through the microbial fermentation of dietary substrates and contribute to the maintenance of intestinal homeostasis.

In addition, markers related to intestinal inflammation, digestion, mucosal immune function, or the intestinal barrier can, when clinically indicated, provide different types of information about the functional status of the gastrointestinal system.

Thus, assessing dysbiosis is more informative when it is not limited to measuring the relative abundance of specific microorganisms, but instead considers the microbiome as part of a broader biological system.

Conditions associated with gut dysbiosis
Research on the gut microbiome has identified associations between alterations in microbial composition or function and a wide range of health conditions. These associations are better established for certain gastrointestinal diseases, while research into many extraintestinal conditions is still evolving.

Gastrointestinal disorders, such as inflammatory bowel diseases, including Crohn’s disease and ulcerative colitis, irritable bowel syndrome (IBS), and Clostridioides difficile infection. Particularly in inflammatory bowel disease, alterations in microbial diversity, composition, and microbiome function have been documented.
Metabolic disorders, such as obesity, insulin resistance, and type 2 diabetes mellitus. Potential mechanisms under investigation include, among others, microbial metabolites, bile acid metabolism, and the regulation of inflammation.
Immune-mediated and allergic conditions, as the gut microbiome interacts closely with the immune system and contributes to the regulation of immune responses. Microbiome alterations have been studied in various autoimmune and allergic diseases, although no single pattern of dysbiosis has been established.
Neurological and neuropsychiatric conditions, through the gut–brain axis, a bidirectional communication system involving neural, immune, endocrine, and metabolic pathways. Microbiome alterations are being investigated in conditions including Parkinson’s disease, Alzheimer’s disease, depression, and anxiety disorders. For most of these associations, however, dysbiosis has not been established as a cause of disease.

In most of these conditions, detecting dysbiosis does not constitute an independent diagnostic criterion, nor does it demonstrate that microbiome alterations cause the disease. The relationship is often bidirectional: disease may affect the microbiome through changes in diet, intestinal motility, inflammation, or medication use, while specific microbial functions may, in turn, contribute to pathophysiological mechanisms.

For this reason, microbiome findings should be interpreted alongside medical history, symptoms, and other laboratory markers. Their clinical value lies not simply in determining that “dysbiosis is present,” but in assessing the nature of the alterations, their potential functional significance, and their relationship to the individual’s overall clinical picture.

Laboratory Investigation of Dysbiosis

The laboratory investigation of dysbiosis may include different categories of tests, depending on the question that needs to be addressed. No single test can determine whether an individual has a “healthy” or “unhealthy” microbiome. For this reason, assessment may combine analysis of the microbial community with markers that provide information about intestinal function.

Analysis of gut microbiome composition
Modern molecular techniques allow the microorganisms present in a stool sample to be analyzed without the need for culture. Two main approaches are:

targeted PCR, as used in EnteroScan®
next-generation sequencing (NGS), as used in EnteroScan® NGS

The 16S rRNA gene plays a central role in the study of bacteria. It is present in all bacteria and contains both conserved and more variable regions. Differences in its sequence can therefore serve as a type of “molecular identity” for identifying and classifying different bacteria.

The two approaches are therefore complementary, and their use depends on the question being addressed: PCR provides targeted information about specific microorganisms, whereas 16S rRNA NGS enables broader profiling of the gut microbiome.

Assessment of intestinal environment function
Analysis of microbial composition can be complemented by markers that assess different aspects of the intestinal environment, such as:

Short-chain fatty acids (SCFAs), important products of microbial metabolism.
Fecal calprotectin, a marker of intestinal inflammation.
Pancreatic elastase, a marker of exocrine pancreatic function.
Secretory IgA (sIgA), which provides information about the immune function of the intestinal mucosa.

Depending on the clinical question, additional markers related to the intestinal barrier or to specific metabolic functions of the gut and microbiome may also be assessed.

The importance of combined interpretation
A result showing an increased or decreased relative abundance of a particular bacterium should not, on its own, form the basis for therapeutic decisions. Similarly, a functional marker may be influenced by factors that are not directly related to the microbiome. For this reason, laboratory investigation is more useful when findings are evaluated alongside symptoms, diet, medication use, history of infections and antibiotic use, and any known medical conditions.

Within the context of functional medicine, the aim is not simply to apply the label of “dysbiosis,” but to identify specific alterations in the composition and function of the intestinal ecosystem that may be related to the individual’s clinical presentation. Combined laboratory assessment can therefore contribute to the selection of a more personalized intervention based on each individual’s findings and needs, rather than applying a general approach to every case of dysbiosis.

Therapeutic Approaches to the Management of Dysbiosis

Dysbiosis management is not based on a single treatment. The aim is to identify and address factors that may disrupt the intestinal ecosystem and support its normal function, based on each individual’s findings and needs.

Diet and Lifestyle
Diet is one of the most important modifiable factors affecting the gut microbiome. A diverse range of plant foods and adequate dietary fiber intake can support microbial metabolism and the production of beneficial metabolites. However, dietary interventions should be adapted to the individual’s tolerance and symptoms. Physical activity, adequate sleep, and the management of chronic stress are also important factors for overall gut health.

Probiotics and prebiotics
Probiotics and prebiotics may be used in selected cases to modify microbiome composition or function. However, they are not a universal treatment for every form of dysbiosis. Select them with a specific purpose, as probiotic effects depend on the strain and indication, and some prebiotics may not be well tolerated by people with pronounced gastrointestinal symptoms.

Addressing underlying factors
When persistent symptoms are present, it is important to investigate possible underlying causes, such as digestive disorders, inflammatory conditions, or infections, rather than automatically attributing the symptoms to dysbiosis. Similarly, the unwarranted use of antibiotics, antimicrobial preparations, or highly restrictive dietary regimens aimed at “eliminating” specific microorganisms may further disrupt the intestinal ecosystem.

Management is therefore more effective when personalized based on the individual’s medical history, symptoms, clinical presentation, and, where indicated, laboratory findings.

Conclusions

Dysbiosis is not a disease or diagnosis in itself, but describes alterations in the composition and/or function of the microbiome, the significance of which depends on the overall clinical context. For this reason, isolated microbial alterations are not sufficient to explain symptoms or determine a therapeutic intervention.

When investigation is indicated, the combined assessment of microbiome composition, selected functional markers, symptoms, and medical history can provide a more comprehensive picture of the intestinal ecosystem. This approach allows specific alterations to be identified and may contribute to the development of more personalized interventions, where necessary.

References

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