Influence of the origin of dietary proteins (plant <i>vs.</i> animal) on the faecal microbiota of older adults

The gut microbiota plays a crucial role in human health and is key to understanding how various factors modulate its composition in older adults, enabling targeted interventions. This study aims to identify how dietary and lifestyle patterns influence older adults' gut microbiota profile, considering the plant-based or animal origin of the dietary protein. A cross-sectional observational study was conducted with older adults aged between 60 and 80. Faecal samples were analyzed to determine gut microbiota composition and assess short-chain fatty acid (SCFA) production. Associations between microbiota profiles, dietary patterns, and metabolic markers were conducted through correlation and <i>t</i> tests. The study revealed that a diet rich in plant-based protein was linked to a lower body mass index (BMI) and to a significantly higher relative abundance of Verrucomicrobiota (4.46%) compared to an animal protein diet (1.47%). Firmicutes was the predominant phylum (61.10% relative abundance), while Proteobacteria levels tended to be higher in individuals with high-fat diets and alcohol consumption. Regarding genera, some of them are directly related to gut microbiota diversity and inversely related to BMI, such as <i>Christensenellaceae</i> R-7 group and <i>Akkermansia</i>. Also, <i>Roseburia</i> was significantly associated with valeric acid levels (<i>r</i> = 0.43, <i>p</i> = 1.5 × 10^-3). High fibre intake was associated with reduced branched-chain SCFA (bc-SCFA) production. Increasing plant-based protein and fibre intake may promote a more favourable gut microbiota composition and enhance resilience against dysbiosis and related age-related conditions. Also, the presence of beneficial genera can increase gut microbiota diversity and decrease BMI, as well as induce healthy gut metabolic profiles. These findings underscore the potential of personalized nutrition and dietary strategies tailored to protein origin and fibre intake to modulate the gut microbiota and improve metabolic health in older adults.