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

Inclusion Criteria: 1. Participant is willing and able to give informed consent for participation in the study. 2. Confirmed diagnosis of sMM according to IMWG criteria 3. Absence of features of symptomatic or active myeloma requiring treatment (myeloma-defining events). 4. Aged ≥18 and \</= 75 years 5. Participant is willing to comply with all study-related procedures. 6. ECOG performance status of 0-1. Exclusion Criteria: 1. Non-Caucasian subjects. Racial disparities in all stages of the disease characterize MM, and Blacks have an increased MGUS and MM risk and higher mortality rate than Whites. 2. Patients that already follow a whole food plant-based diet (≥ 40g/die;ovo-lacto-vegetarian or processed junk food vegan diets are not excluded). These patients likely should already have high SCFA levels in their gut. 3. Legume allergy. 4. Severe allergies such as anaphylactic shock to nuts (specifically cashews). 5. Concurrent participation in weight loss/dietary/exercise programs because of potential conflicts between the concurrent diet and high-fiber diet. 6. Enrollment onto any other therapeutic investigational study. 7. Concurrent pregnancy. 8. Ongoing treatment for HBV, HCV or HIV. 9. If in the opinion of the investigator there maybe any concerns regarding the ability of the patient to complete the study safely or any contraindications. 10. Heavy drinker (defined as \>2 drinks per day or \>14 drinks per week). 11. Current self-reported illicit drug use (e.g., heroin, cocaine not marijuana). 12. Subjects that did not accept to sign the informed consent. 13. Subjects reporting infectious diseases requiring antibiotic therapy in the previous three months, ongoing antibiotic therapy, or prophylaxis. Antibiotic therapy dramatically modifies the composition of the gut microbiota. 14. Subjects affected by autoimmune diseases except for thyroiditis, and patients affected by small and large intestine dysfunctions (i.e., inflammatory bowel disease). 15. Gammopathy-associated conditions beyond sMM (e.g. amiloydosis, POEMS, LCDD, etc).