There are age-related changes in the gastrointestinal tract. The difficulty is that with age it can be difficult to exclude pathological factors such as diabetes, pancreatitis, liver disease and malignancy, since these factors will have potential adverse effects on the intestine.

Selective neurodegeneration of the aging enteric nervous system can lead to gastrointestinal symptoms such as dysphagia, gastrointestinal reflux and constipation. 6 Caloric reduction in rodents can prevent neuronal loss, suggesting that diet may influence the aging gut.7 Esophageal motility may reduce the reduction of neurons in the mesenteric plexus in older people.8 Gastric motility is impaired with aging9 but the small intestine is unaffected.10 With age colonic motility can be influenced by signal transduction pathways and cellular mechanisms that control smooth muscle contraction which could lead to constipation.11

Reduced gastric acid secretions have an increasing prevalence with aging. Hypochlorhydia occurs due to chronic gastritis. Consequently, proton pump inhibitors are frequently used for prolonged periods in older people leading to suppressed acid secretions. Procedures such as vagotomy and gastric resections (both seen in older people) cause reduced acid levels. The overall reduction in acid secretions predisposes the gut to small bowel bacterial overgrowth.12 One study highlighted that 71% of patients on a geriatric ward had bacterial overgrowth of the small intestine and 11% were found to be malnourished.13 Bacterial overgrowth has been proven to be associated with reduced body weight and reduced intake of micronutrients.14

Structural changes of the pancreas are seen with aging, but no functional age-related changes are seen with the fluorescein dilaurate test.15 Secretagogue-stimulated lipase, chymotrypsin and bicarbonate concentration in pancreatic juice have all been shown to decline with aging.16 Other studies found little evidence of reduced pancreatic secretion with age-independent of factors such as disease and drugs.17 The liver declines in size and blood flow with age but microscopic changes are subtle.18 In mice with age it has been shown that changes in the expression of genes in the liver are involved in inflammation, cellular stress and fibrosis.19 Caloric restriction in mice appeared to reverse age-related changes, indicating that diet influences age-related changes.20 Changes can occur in the small intestine such as decline in the number of villi and crypts,18 loss of villi and enterocyte height21 and decline in mucosal surface.22 However, there is no clear association between intestinal morphology and nutrient uptake with aging.23