A high-fiber plant-based dietary intervention may improve gut microbiome composition in patients with precursor plasma cell disorders, potentially offering the first dietary strategy to delay progression to active multiple myeloma, according to results from a clinical trial at Memorial Sloan Kettering Cancer Center.
In the single-arm pilot study (ClinicalTrials.gov identifier NCT04920084), researchers assigned 20 patients with monoclonal gammopathy of undetermined significance (MGUS)/smoldering multiple myeloma (SMM) and a BMI of more than 25 kg/m² to follow a high-fiber plant-based dietary intervention for 12 weeks followed by 24 weeks of behavioral counseling. Median dietary adherence increased from baseline (20%) to week 12 (91%), while median BMI decreased from baseline (34.3 kg/m²) to week 12 (–6.6%).
Microbiome and Dietary Quality Improvements
The intervention produced substantial improvements across multiple dietary and microbiome parameters. The median dietary fiber intake nearly doubled from baseline (12.3 g/1,000 kcal/day) to week 12 (24 g/1,000 kcal/day. The Healthy Eating Index (HEI)-2020 score increased from baseline (61.4) to week 12 (80).
Gut microbiome analysis revealed positive changes. Median fecal microbiome α-diversity by 16S sequencing increased from baseline (6.18) to week 12 (8.42). The relative abundance of butyrate producers increased from baseline (median = 0.03) to week 12 (0.08).
Correlations Between Diet and Microbiome
The researchers identified multiple statistically significant correlations between dietary parameters and microbiome composition. Alpha diversity correlated negatively with BMI (P < .001) and positively with fiber intake (P = .004), HEI-2020 scores (P = .017), and dietary adherence (P = .001).
Fiber intake (P = .014), HEI-2020 scores (P = .006), and dietary adherence (P = .002) were positively correlated with a higher relative abundance of butyrate producers. The study authors noted that "consistent findings were seen at [week] 24 and [week] 52."
Clinical Significance and Background
MM represents the second most common hematologic malignancy and is typically preceded by precursor conditions. The study authors noted that "elevated BMI, poor dietary quality, and microbiome dysbiosis are risk factors for development of MGUS/SMM and MM progression."
The intervention protocol required patients to maintain weekly food logs for accountability, with 3-day food records clarified prior to dietitian visits. All food records underwent analysis using ASA24 software. Dietary adherence was calculated as the percentage of kcals from minimally processed plant foods out of total kcals consumed.
First-of-Its-Kind Research
"This is the first interventional clinical trial to show that a [high-fiber plant-based diet] can improve dietary quality and [the] microbiome with potential to delay progression of MGUS/SMM to MM. To our knowledge there has been no similar dietary intervention in [hematologic malignancies]," noted study investigators. "The [diet] was safe, feasible, and improved diet quality and [the] microbiome." The primary endpoint of feasibility was measured by dietary adherence and BMI reduction, both of which showed statistically significant improvements.
Study Design and Methodology
The research team, led by presenting author Francesca Castro, MS, RD, CDN, employed a comprehensive approach to dietary assessment and microbiome analysis. Secondary and exploratory endpoints included dietary quality assessment through HEI-2020 scores and fiber intake measurements, alongside detailed microbiome profiling.
The 12-week intensive dietary intervention period was followed by an extended 24-week behavioral counseling phase, allowing the researchers to assess both the short-term and sustained effects of the intervention.
Funding and Support
The study received support from multiple sources, including the National Institutes of Health/National Cancer Institute Cancer Center Support Grant, Paul Calabresi K12 Award, the Allen Foundation, and the Paula and Rodger Riney Foundation.
Source: Nutrition 2025
