The researchers are doing this study to look at how butyrate levels change in participants' stool after they are on a- plant-based diet for at least 12 weeks. All participants will have monoclonal gammopathy of undetermined significance (MGUS) or smoldering multiple myeloma (SMM). We will compare how the plant-based diet, omega-3 fatty acid and curcumin supplements, and placebo (an inactive substance that looks like the study supplements) affect butyrate levels in participants' stool.

Inclusion Criteria:

• Confirmed diagnosis of MGUS or SMM
• If non light chain MGUS/SMM then M spike must be either ≥ 0.2 g/dL or BM PC ≥10% (both not required)
• If light chain MGUS/SMM then involved must be ≥10 mg/dL or BM PC ≥10% (both not required)
• If IgA MGUS/SMM then an IgA level >350 mg/dL and an abnormal immunofixation is required (M spike criteria not required).
• If IgD MGUS/SMM then an IgD level >50 mg/dL and an abnormal immunofixation is required (M spike criteria not required).
• Age ≥18 years
• Willingness to comply with all study-related procedures
• ECOG performance status of 0-3
• Interested in learning to cook plant based recipes

Exclusion Criteria:

• Patients that already follow a whole foods plant based diet (ovo-lacto-vegetarian or processed junk food vegan diets are not excluded)
• Legume allergy
• Severe allergies such as anaphylactic shock to nuts (specifically cashews). Peanuts are not included in the meals.
• Concurrent participation in weight loss/dietary/exercise programs
• Mental impairment leading to inability to cooperate
• Enrollment onto any other therapeutic investigational study concurrently and up to 180 days prior to study start date
• Concurrent pregnancy
• Positive HBV, HCV or HIV PCR test will need to be treated first and once undetectable viral load patients may enroll
• ≥ Grade 2 electrolyte abnormalities as defined by CTCAEv5.0 (need to be resolved before enrolling on study)
• 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
• Heavy drinker (defined as >2 drinks per day or >14 drinks per week)
• Current self-reported illicit drug use (eg heroin, cocaine not marijuana)
• Plan for prolonged travel during the study that would preclude adherence to prescribed diets
• History of major gastrointestinal surgery (not including appendectomy or cholecystectomy) within 3 months of enrollment
• If already taking curcumin or omega 3 supplements patients must be willing to stop it on the date of trial consent for study duration.

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org