Ageing and the gut.

The goal of this brief review is to address the role of the ageing gut in the genesis of malnutrition in the elderly. We assess the burden of malnutrition in the elderly, exploring the role of comorbid conditions and neurohumoral changes that take place to contribute towards the process of anorexia associated with ageing. Following this, the review assesses physiological changes that occur in each part of the gastrointestinal (GI) tract and what implication they may have in clinical practice. In the oropharynx and the oesophagus, changes in swallowing and oesophageal motility associated with ageing can be demonstrated using physiological testing. However, in the absence of comorbid disease, they often have little, if any, clinical significance. In the stomach, reduced fundal compliance may contribute to early satiety; however, the primary change is hypochlorhydria, which may predispose to malabsorption or bacterial overgrowth further along the GI tract. Almost uniquely, the small bowel, particularly its absorptive function, is unaffected by age and we review the literature demonstrating this. In the colon, there is evidence of a prolonged transit time related to a reduction in both neurotransmitters and receptors. Although this may cause symptoms, this aspect is unlikely to contribute to malnutrition. In addition, we assess the potential changes in the gut microbiome and how this may interact with the immune system in the process of 'inflamm-ageing'. We conclude by summarising the main changes and their impact for the clinician along with recommendations for future areas of research.