The development of preventative nutritional strategies to promote healthy ageing is becoming increasingly important. Elevated thresholds for taste and smell, coupled with swallowing difficulties and masticatory dysfunction, often result in nutritionally imbalanced diets among the elderly. This can induce great changes in the composition and metabolic activities of the gut microbiome, leading to decreased intestinal motility and impaired bowel function. This can result in constipation or diarrhoea, increased basal levels of inflammation, immunosenescence and morbidity. The objectives of this study are to use dietary modification to improve gut health in older people. Diets high in resistant starch or dietary fibre will be given to 50 elderly volunteers (70-95 years) living in the community, in a randomised double-blind cross-over study. The aim is to investigate the effects on microbiome composition and functionality through fermentation, reduced putrefaction, and modification of blood markers associated with obesity and diabetes.

Inclusion Criteria:

• Men and women aged 70-95 years, with BMI 18.5-30.0 kg m2.

Exclusion Criteria:

• Exclusion criteria will include asplenia and other acquired or congenital immunodeficiencies
• Any autoimmune disease
• Self-reported symptoms of acute or recent infection (including use of antibiotics within the previous 3 months)
• Taking probiotics or prebiotics, including lactulose for constipation
• Chronic gastrointestinal problems (e.g. Inflammatory Bowel Disease, Irritable Bowel Syndrome, cancer).
• Specifically, volunteers who are diabetic will not be excluded from the investigation.
• Assessment will be on a case by case basis.