A Prospective Multicenter Study of the Effects of Plant-based Diets on Gut Microbiome and Derived Metabolites in Patients Affected by Smoldering Multiple Myeloma

Our overarching hypothesis is that plant-based diets will induce beneficial modifications of the gut microbiota favoring short fatty acid (SCFA)-producing commensals and a more advantageous CD8/Th17 ratio in sMM patients, thus preventing evolution to MM. Goal of this national, prospective, multicenter study is to demonstrate that plant-based diets substantially modify the gut microbiome inducing increased production of SCFAs in patients affected by sMM. The study will involve up to 62 patients affected by sMM. 56 Enrolled and eligible patients will be encouraged to consume a balanced diet rich in fiber for the entire duration of the trial (i.e., 12 weeks). Patients will choose among a list of different diet plans or individual food according to the personal tastes and preference. Free outpatient medical visit will be performed at enrollment and at week 12, and nutritional counseling will be given at the time of enrollment, one month later and on demand. As in line with routine diagnosis and follow-up of for patients affected by sMM, the investigators will collect bone marrow aspirates and peripheral blood at the time of screening, for plasma, serum, and peripheral blood mononuclear cells (PBMCs), while stool samples will be collected immediately before diet initiation. The investigators will also collect stool samples 4 and 12 weeks after diet initiation, and peripheral blood at 12 weeks after study initiation (as per routine clinical follow-up of this patient population). Dietary measurements will be conducted along the entire duration of the nutritional regimen by questionnaires. Biological paired comparison will be conducted between data obtained from samples collected at time 0 and samples collected 4 and 12 weeks later.