Elsevier

The Lancet

Volume 361, Issue 9356, 8 February 2003, Pages 512-519
The Lancet

Review
Gut flora in health and disease

https://doi.org/10.1016/S0140-6736(03)12489-0Get rights and content

Summary

The human gut is the natural habitat for a large and dynamic bacterial community, but a substantial part of these bacterial populations are still to be described. However, the relevance and effect of resident bacteria on a host's physiology and pathology has been well documented. Major functions of the gut microflora include metabolic activities that result in salvage of energy and absorbable nutrients, important trophic effects on intestinal epithelia and on immune structure and function, and protection of the colonised host against invasion by alien microbes. Gut flora might also be an essential factor in certain pathological disorders, including multisystem organ failure, colon cancer, and inflammatory bowel diseases. Nevertheless, bacteria are also useful in promotion of human health. Probiotics and prebiotics are known to have a role in prevention or treatment of some diseases.

Section snippets

Composition of the flora

Colonisation of the gastrointestinal tract of newborn infants starts immediately after birth and occurs within a the birth canal versus caesarean section) and the type of diet (breast versus formula feeding) might affect the colonisation pattern.7, 8, 9, 10 Other environmental factors also have a major role since differences exist between infants born in developed countries and those born in developing countries, and between infants from different hospital wards.11, 12, 13 Pioneer bacteria can

Main functions of microflora

Use of animals bred under germ-free conditions has provided important information about the effect of the microbial community of the gut on host physiology and pathology.24 Evidence obtained through such studies25 suggests that microflora have important and specific metabolic, trophic, and protective functions (panel).

Translocation of bacteria

The passage of viable bacteria from the gastrointestinal tract through the epithelial mucosa is called bacterial translocation.70 Translocation of endotoxins from viable or dead bacteria in very small amounts probably constitutes a physiologically important boost to the reticuloendothelial system, especially to the Kupffer cells in the liver. However, dysfunction of the gut mucosal barrier can result in translocation of many viable microorganisms, usually belonging to gram-negative aerobic

Colon cancer

The molecular genetic mechanisms of colorectal cancer are well established, but environmental factors such as diet might also have a major role in development of sporadic colon cancer. Dietary fat and high consumption of red meat, especially processed meat, are associated with high risk of colon cancer.76 By contrast, a high intake of fruits and vegetables, whole grain cereals, fish, and calcium has been associated with reduced risk.76, 77 Dietary factors and genetic factors interact in part

Inflammatory bowel diseases

Resident bacterial flora have been suggested to be an essential factor in driving the inflammatory process in human inflammatory bowel diseases.86 In patients with Crohn's disease, intestinal T lymphocytes are hyperreactive against bacterial antigens, and Pirzer and colleagues87 suggested that local tolerance mechanisms are abrogated in such patients. In addition, patients with Crohn's disease or ulcerative colitis have increased intestinal mucosal secretion of IgG type antibodies against a

Probiotics and prebiotics

Bacteria can be used to improve human health. A bacterium that provides specific health benefits when consumed as a food component or supplement would be called a probiotic. A consensus definition of the term was issued a few years ago and states that oral probiotics are living microorganisms that upon ingestion in specific numbers, exert health benefits beyond those of inherent basic nutrition.102 According to this definition, probiotics do not necessarily colonise the human intestine. The

Recommendations

A better understanding of our relations with the microbial world should help in prevention of diseases such as atopy, colon cancer, and inflammatory bowel diseases.

Search strategy and selection criteria

In writing this review, we relied on original articles and reviews that were published in scientific journals and are searchable in database libraries (OVID, PubMed, Medline Plus Databases), and on our current readings on the topic. Due to space limitations, the number of studies quoted has been restricted. We chose articles for citation on the basis of the relevance of its contents without any bias toward author or journal.

Conflict of interest statement

F Guarner and J-R Malagelada are

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