This study assesses the effects of an oral nutritional supplement (ONS) with fibre compared to a non-fibre containing ONS equal in energy and protein content on gut microbiota bifidobacteria in older adults with or at risk of disease related malnutrition. It is a randomised controlled, double blind, parallel-group, multi-country study. Subjects will receive an ONS with or without (control group) fibre. They take it twice a day for 4 weeks and the change in their gut microbiota bifidobacterial levels is the primary outcome. They will be measured at day 1 (V1), day 15 (V2) and week 4 (V3).