Volume 9 Issue 10, October 2012

New findings demonstrate novel interactions between diet, bacteria, genetic susceptibility and immune responses in IBD. Milk fat increases production of taurocholine-conjugated bile acids, which promotes growth of sulphate-reducing bacteria that cause immune-mediated colitis in susceptible mice. These observations will guide human studies that might improve dietary advice for patients with IBD.

Metagenomic and metabonomic analysis suggests that age-associated stability of the intestinal ecosystem is strongly influenced by an individual's social and dietary status. The process of immunosenescence might serve as a causal link to explain the association between a perturbed distal gut microbiota and frailty in the elderly.

The development of the gut microbiota occurs early in life. As outlined in this Review by Isolauri and colleagues, the initial microbial colonization of the gut, and indeed of the rest of the human body, is a stepwise process and interactions between these colonizing bacteria and the human host ultimately have a key influence on health and disease.

The human gut harbours a vast array of micro-organisms and the benefits of these bacteria should not be forgotten. Here, Flint and colleagues discuss the role of the gut microbiota in nutrition and health, describing the development of these bacteria in the healthy gut, and their positive influences on microbial and human metabolism.

The gut microbiota is recognized to have a role in the development of obesity, and evidence indicates that the composition of the microbiota is modified after bariatric surgery. This Review summarizes current knowledge of the potential mechanisms by which major modifications of the digestive tract after bariatric surgery can affect the composition of the gut microbiota.

IBD is emerging as a worldwide epidemic. Patients with IBD often have an abnormal gut microbiota; however, it is unknown whether this feature is a cause or a consequence of disease. In this article, Francisco Guarner and colleagues review our current knowledge of the human gut microbiota, describe changes observed in patients with IBD and discuss whether such changes might explain the pathophysiological characteristics of IBD.

The changing composition of the human microbiota is linked with alterations in human behaviour and the rising prevalence of immunoallergic and metabolic disorders. In this article, Fergus Shanahan discusses the clinical implications of advances in human microbial ecology; the lessons learned extend beyond the gut and are germane to all clinical specialities.

Research into the human microbiota has rapidly expanded in the past few years, and the field continues to evolve at an unprecedented pace. The four Reviews, one Perspectives and two News & Views articles in this Focus issue on the gut microbiota outline the latest developments in this exciting new field, providing clinicians and researchers alike with a vital insight into the gut–microbiota relationship in human health and disease, and the implications for clinical practice. The development of the gut microbiota in infancy and old age, and its beneficial role in nutrition and health are discussed, alongside the role of this microbial 'organ' in IBD, the effects of bariatric surgery and the clinical potential of harnessing our gut microbiota.