Maintaining health is a question of balance
The human body and its microbiomes work to help the immune system function normally. Understanding how they become imbalanced provides an important foundation for research.
How imbalances can affect human health
The human body and its microbiomes are in a dynamic state of balance. Multiple systems continuously interact to maintain normal function. This balance - or homeostasis - applies to the body’s own processes and also the microbial ecosystems living within it.
Just as the body can become imbalanced, so too can the microbiome. Such changes do not occur in isolation. The two are closely connected and changes in one can influence the other. In this way, imbalances in microbial communities may affect body function, while changes in the body’s internal environment can shape the microbiome.
Microbial diversity helps support resilience
Diversity is a key characteristic of the microbial ecosystem. Higher microbial diversity is generally linked to a wider range of functions and greater resilience, although what is considered optimal can differ between individuals and contexts.
Modern life - things like diet changes, antibiotic exposure, sanitation and even urbanization can influence the microbiome’s composition and diversity - often to its detriment.
These broader environmental and lifestyle changes have occurred rapidly in evolutionary terms. This may contribute to a mismatch between human biology - including microbiomes - and modern living conditions.
Understanding how such imbalances arise and how they may influence different aspects of health provides an important foundation for exploring specific health outcomes.
Immune health
The immune system plays a central role in protecting the body while maintaining tolerance to harmless substances and beneficial microorganisms.
A large part of the immune system is closely associated with the gastrointestinal tract where it continuously interacts with the gut microbiome. This is essential for immune development and regulation.
Microbial signals help shape immune responses, supporting the balance between activation and tolerance. In turn, the immune system influences which microorganisms can persist in the gut. This contributes to the microbiome’s overall structure. When balanced, this interaction supports appropriate immune function. It also helps the body to respond effectively to external challenges while avoiding unnecessary or excessive immune reactions.
What happens when there's an imbalance
The immune system and the gut microbiome are closely interconnected and continuously interact as part of normal physiological processes. Challenges affecting either system may influence their interaction, which plays a role in immune regulation and the balance between immune activation and tolerance.
Research has shown that differences in the gut microbiome are associated with differences in immune function and how the body responds to immune challenges. These include challenges affecting the respiratory tract, as well as immune-related conditions such as allergies and food intolerances. While these relationships are complex and not yet fully understood, they highlight the role of the gut microbiome in shaping immune activity both locally in the gastrointestinal tract and beyond.
Understanding how the gut microbiome interacts with the immune system provides insight into the biological processes that help maintain normal immune function across different stages of life.
Your gut and digestion
The gut microbiome and digestive health
Digestive health reflects the proper functioning of the gastrointestinal system, including digestion, absorption, barrier function, and communication with other systems in the body.
It is shaped by interactions between human physiology, the gut microbiome, digestive chemistry, and nutritional inputs. When this system is in balance, the gut can efficiently break down and absorb nutrients, maintain the gut barrier, and support signaling within the gut as well as between the gut and other organs.
The gut microbiome plays a central role in these processes.
Effects of gut microbiome disruption
When the balance between the gut microbiome, digestive processes, and the body is disrupted, changes in microbial composition or activity may influence digestive function. This can affect nutrient processing, alter microbial metabolism, and impact the gut barrier, potentially increasing its permeability and modifying interactions between the gut and its surroundings.
These changes are associated with gastrointestinal symptoms including diarrhea, constipation, abdominal discomfort, and bloating. They are commonly observed in disorders such as irritable bowel syndrome (IBS).
Imbalances in the gut environment may also influence how the gastrointestinal system responds to external challenges, including exposure to pathogens, and may affect susceptibility to gastrointestinal infections.
Early life and digestive system development
In early life, when the gut microbiome and digestive system are still developing, interactions between microbial activity, gut function, and gut–brain signaling are not yet fully established. This developmental stage is being studied in relation to conditions such as infant colic, where altered gut function and microbial activity may play a role.
Understanding how the gut microbiome interacts with the broader gut system provides insight into the mechanisms underlying digestive health and how it may be affected across different stages of life.
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