FAST-M: Prolonged Overnight Fasting and Mediterranean Dietary Intervention for Patients With Multiple Myeloma or Its Precursor Disease

Inclusion Criteria: 1. 18 years of age or older. 2. Any sex/gender. 3. Able to provide consent. 4. Able to speak, read, and understand English or Spanish. 5. Diagnosis of Monoclonal Gammopathy of Undetermined Significance (MGUS), Smoldering Multiple Myeloma (SMM), or Multiple Myeloma (MM) per standard criteria: 1. Cohort 1 - Participants must have a confirmed diagnosis of MGUS and SMM. 2. Cohort 2 - Participants must have a confirmed new diagnosis of MM and be initiating anti-myeloma therapy. 6. Delivery of anti-myeloma therapies at one of the following institutions: 1. Sylvester Comprehensive Cancer Center (SCCC) (including satellite/network sites). 2. University of Miami Health System. 7. Approval from treating oncologist, confirmed via email or in writing. 8. Eastern Cooperative Oncology Group (ECOG) Performance Status grade of \<2 a. PI approval needed if ECOG ≥ 2. 9. Having not consistently (not equal to or more than 50% of the time) engaged in structured fasting (i.e., not regularly fasting for ≥12hr/night) for the past 3 months. 10. Not consuming a Mediterranean diet by not meeting 2 or more out of the following 3 Mediterranean eating pattern goals in the prior 3 months: ≥3 servings of vegetables per day, ≥ 3 servings of beans and legumes per week, or ≥ 1 serving of nuts per day. Mediterranean diet will be screened with select components of a Mediterranean Diet Adherence Screener (MEDAS). 11. Internet access on a smart phone, tablet, or computer. 12. Willing to be randomized to a prolonged overnight fasting and guided Mediterranean dietary intervention or waitlist-control group. Exclusion Criteria: 1. Individuals younger than 18 years of age. 2. Unable to provide consent. 3. Unable to read or understand English or Spanish. 4. Any contraindication for diet changes as determined by physician. 5. History of a clinical eating disorder. 6. History of dementia or major psychiatric disease. 7. History of recent (≤1 yr) stroke, myocardial infarction or congestive heart failure. 8. History of autoimmune disease and on treatment at time of screening.