The role of diet and dietary patterns in the composition of gut microbiota (GUTDIET-PT): A multicentre cross-sectional observational study

Background: The gut microbiome plays a fundamental role in human health, influencing immune, metabolic, and nutritional functions. Diet is a key factor in shaping microbiota composition, with dietary patterns like the Mediterranean Diet (MD) and Plant-Based Diets (PBD) associated with greater microbial diversity and beneficial bacteria. In contrast, the Western Diet (WD) has been associated with reduced diversity and increased risk of disease. Methods: The GUTDIET-PT study is a multicentre, cross-sectional observational study aiming to recruit 2,500 healthyparticipants aged 40 to 74. It is part of the GUTBIOME-PT (NCT06741293), a larger project designed to improve colorectal cancer (CRC) screening in Portugal. Socio-demographic and anthropometric data (weight and height) will be collected via self-administered questionnaires. Dietary intake will be assessed using two non-consecutive 24-hour dietary recalls, and principal component analysis (PCA) will be used to identify and characterise dietary patterns. Additionally, adherence to the MD and PBD will be evaluated using validated tools such as the Mediterranean Diet Adherence Score and the Plant-Based Dietary Index, while the inflammatory potential of the participants’ diet will be assessed through the Dietary Inflammatory Index. Gut microbial composition and functional capacity will be determined by shotgun metagenomic sequencing of faecal samples. Discussion: By combining advanced microbiota analysis with detailed dietary assessments through structured nutritional interviews, we aim to provide novel insights into the relationship between dietary patterns and gut microbiota composition and function. Additionally, focusing the study on healthy individuals will allow us to characterise the microbiota in the absence of disease, offering a clearer understanding of the features of a “healthy” microbiome. This study will establish a foundational framework for identifying dietary patterns that promote microbial diversity and functionality, contributing to tailored nutritional recommendations and public health strategies aimed at improving gut health. Trial Registration: NCT06741293