What do we mean when we talk about the gastrointestinal system? Understanding the foundations of digestive health

At first glance, the gastrointestinal system may seem to be simply the group of organs responsible for digesting food and absorbing nutrients. But this definition falls far short of capturing its full biological relevance, as digestion is only one part of the story.

In addition to functioning as a dynamic interface between the body and the external environment, it plays an active role in immune regulation. It also harbors trillions of microorganisms that profoundly influence human health, and maintains continuous communication with other organs.

What is digestive health?

When we talk about digestive health, we often think only of the absence of symptoms such as abdominal pain, reflux, bloating, constipation, or diarrhea. But this definition is too limited. In a broader sense, digestive health involves the proper functioning of the gastrointestinal tract, without active disease or symptoms that impair quality of life, as well as key biological processes that help maintain the body’s overall balance.¹

In fact, the digestive process is coordinated and begins even before food is ingested. Stimuli such as the smell and sight of food, as well as the sensation of hunger itself, already trigger responses that prepare the gastrointestinal tract. The stomach and intestines then work together to regulate the release of acid and enzymes, as well as the rate at which ingested food moves through the gut. Further along, the colon absorbs water, stores indigestible waste, and coordinates evacuation.² Under normal conditions, all of this occurs without our awareness; yet a substantial proportion of the population, approximately 30 to 40%, experiences digestive symptoms, often triggered by food intake.³

This variability highlights that digestive health is not only about how the system functions under normal conditions, but also about how it responds to different internal and external influences. Diet and lifestyle play a central role, but environmental and social conditions are also important. Access to safe food and water, exposure to infections, alcohol consumption, smoking, and nutritional status throughout life can all affect how the digestive system functions and adapts.⁴

Much more than a digestive tube

Reducing the gastrointestinal tract to a simple “digestive tube” is to overlook its complexity. From the oral cavity to the colon, this system coordinates motility, secretion, digestion, and absorption, while also performing essential barrier and defense functions. The intestine, in particular, plays a central role in this dynamic by maintaining an epithelial interface in constant interaction with the immune system and with the microorganisms present in the intestinal lumen.⁵ Recognizing this complexity also means understanding that digestive health is not confined to the clinic or the laboratory, but is a central public health issue.

The role of the gut microbiota

Advances in gut microbiome research have made our understanding of its role in digestive health both clearer and more clinically relevant. In areas such as metabolic health, gastrointestinal disorders, neurogastroenterology, and precision nutrition, recent studies have highlighted the microbiome’s central role in promoting health and guiding future therapeutic innovations.

In addition, the gut microbiota contributes to the metabolism of nutrients and other dietary components, helping break down substances that the human body could not digest on its own, participates in the fermentation of food substrates, the production of bioactive metabolites, the synthesis of certain vitamins, and the modulation of bile acid metabolism.⁷

A system connected to the whole body

Another essential point is that the gastrointestinal system does not function in isolation. It is now clear that the gut maintains continuous communication with other organs through neural, immune, endocrine, and metabolic pathways. This integration is particularly evident and has been extensively studied in the gut–brain and gut–liver axes, in which signals derived from the microbiota, the intestinal barrier, and local metabolism can influence systemic functions and contribute to physiological and pathological processes beyond the digestive tract.

This integrated view highlights the gastrointestinal system as a center of physiological regulation, where local intestinal processes have wide-ranging effects on the health of the entire body. For example, through the gut–kidney, gut–lung, and gut–reproductive tract axes, as well as through its important role in cardiovascular health and the stress–circadian axis. Maintaining digestive health, therefore, involves not only digestion, but also the complex interactions between the gut microbiota, the immune system, the nervous system, and endocrine signaling.

Why it matters

Ultimately, understanding the gastrointestinal system means recognizing it as a complex system that integrates digestion, intestinal barrier function, immunity, the microbiota, and communication with other organs. From this perspective, digestive health is no longer defined simply by the absence of symptoms, but rather as a fundamental part of the body’s physiological balance.

In this sense, digestive health is not only about avoiding symptoms, but about supporting one of the key systems that helps keep the entire body in balance.

In this context, World Digestive Health Day (WDHD), a global initiative led by the World Gastroenterology Organisation⁶ and celebrated every May 29, serves as a reminder that, despite important progress — including reduction in childhood mortality from diarrhea — digestive diseases remain a major global health challenge. Addressing them requires sustained efforts to improve prevention, awareness, and access to evidence-based care.

References:

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2.Farré R, Tack J. Food and symptom generation in functional gastrointestinal disorders: physiological aspects. Am J Gastroenterol. 2013 May;108(5):698-706. doi: 10.1038/ajg.2013.24.

3.Houghton LA, De Giorgio R, Boeckxstaens GE, Cryan JF, D’Amato M, Dinning PG, Hasler WL, Vanuytsel T. Fundamentals of Neurogastroenterology: Physiological Aspects and Clinical Implications. Gastroenterology. 2026 Feb 17:S0016-5085(26)00131-9. doi: 10.1053/j.gastro.2026.02.004.

4.Jiang F, Li X, Chen Y, Zhang L, Wang L, Liu Y, Han Z, Cao Y, Ning S. Global, regional, and national burden of nonmalignant digestive diseases, 1990-2023: a systematic analysis from the GBD study 2023. Int J Surg. 2026 Feb 12. doi: 10.1097/JS9.0000000000004481.

5.Takiishi T, Fenero CIM, Câmara NOS. Intestinal barrier and gut microbiota: Shaping our immune responses throughout life. Tissue Barriers. 2017 Oct 2;5(4):e1373208. doi: 10.1080/21688370.2017.1373208.

6. https://wdhd.worldgastroenterology.org/ongoing-wdhd-campaigns/wdhd-2026

7. Rowland I, Gibson G, Heinken A, Scott K, Swann J, Thiele I, Tuohy K. Gut microbiota functions: metabolism of nutrients and other food components. Eur J Nutr. 2018 Feb;57(1):1-24. doi: 10.1007/s00394-017-1445-8.