The November Nutrition Society Paper of the Month is from Proceedings of the Nutrition Society  and is entitled “Gut microbiota in older subjects: variation, health consequences and dietary intervention prospects”.

Composed of trillions of microbes, the gut microbiota is a diverse ecosystem residing in the healthy human intestine, and collectively known as the gut microbiota. A wealth of research has focused on this commensal bionetwork of late and its implications for health are beginning to emerge. Our knowledge of the human microbiome (the collection of genes/coding capacity of the microbiota) has expanded dramatically in the last decade due to culture-independent methodologies. The predominant method of studying this complex ecosystem is by determining the faecal microbiota profile which consists of ten major bacterial divisions or phyla.

Differences in the gut microbiota have been noted across the lifespan, especially at the extremes of life, in infancy and old age. Furthermore, distinct alterations in intestinal microbiota composition and function have been linked to various chronic conditions including obesity, functional gastrointestinal disorders and diabetes. In addition, evidence is emerging for a role of the gut microbiota in colorectal cancer.

The role of microbiota in obesity is probably the most investigated. Three main theories have been suggested as how the microbiota may be involved including inflammation – adipogenesis, influencing energy harvest and controlling bile acid signalling. It is most likely that an over-consumption of an imbalanced diet may alter the gut microbiota profile, and thus reduce diversity and increase energy harvest, potentiated by altered inflammatory tone. However clinical interventions are needed to determine cause and effect and relative contributions of microbiota-related factors.

The gut microbiota is also responsible for indigenous production of specific micronutrients (including B vitamins and vitamin K) and given the fact that habitual human diet interacts with the gut ecosystem on a continuous basis, studies investigating the modulatory effects of specific food ingredients on the gut microbiota are required. The effects of both prebiotics and probiotics have been described with the preponderance of evidence for probiotics pointing to their bifidogenic effect. Selected fermentable prebiotics appear to enhance the production of short-chain fatty acids which have been shown to have both immunomodulatory and anti-inflammatory effects. Despite their potential benefits, further investigations are required to confirm the mechanisms involved and their potential to alter the gut microbiota in specific population groups.

Our findings from the ELDERMET study to date indicate that a diet characterized by a reduced Healthy Food Diversity index leads to a reduced diversity microbiota. This microbiota in turn correlates with reduced scores for a number of health indices including increased frailty, reduced cognitive function, and increased sarcopenia. As previously noted, we cannot distinguish between correlation and causation from a cross-sectional study, therefore intervention studies in pre-clinical models and human subjects are required, and are on-going. Mechanistic studies are required to determine how the gut microbiota may influence specific disease states including age-related health issues, while further characterisation of specific food ingredients is required to understand their modulatory role on specific species within the microbiota. In addition, the ability of specific functional ingredients to increase microbiota diversity and “restore” reduced gut microbiota diversity needs to be explored.

This paper is freely available for one month via the following link: journals.cambridge.org/ns/nov14

Nutrition Society Paper of the Month

Each month a paper is selected by one of the Editors of the five Nutrition Society Publications (British Journal of Nutrition, Public Health Nutrition, Nutrition Research Reviews, Proceedings of the Nutrition Society and Journal of Nutritional Science). This paper is freely available for one month.