A pilot study presented at NUTRITION 2025, the annual meeting of the American Society for Nutrition, highlights the potential of a high-fiber plant-based diet (HFPBD) as a beneficial intervention for patients with monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM). These precursor conditions often precede multiple myeloma (MM), an incurable blood cancer, making strategies to delay progression critically important.
The single-arm pilot trial, led by Francesca Castro, R.D., from the Memorial Sloan Kettering Cancer Center in New York City, enrolled 20 patients with a body mass index (BMI) and a diagnosis of MGUS or SMM. Participants underwent a 12-week HFPBD intervention, complemented by 24 weeks of behavioral counseling. The primary aim was to assess the safety and feasibility of the diet, along with its impact on diet quality and the gut microbiome.
The results demonstrated compelling improvements across several key indicators. Dietary adherence dramatically increased from a median of 20% at baseline to 91% by week 12, indicating the feasibility and acceptability of the HFPBD. This adherence correlated with a significant decrease in median BMI by 6.6%, a crucial factor given that elevated BMI is a known risk factor for both MGUS/SMM development and MM progression. Furthermore, median dietary fiber intake nearly doubled from 12.3 to 24 g/1,000 kcal/day, and the median Healthy Eating Index (HEI)-2020 score, a measure of overall diet quality, improved substantially from 61.4 to 80.
Beyond macroscopic dietary changes, the study delved into the micro-level impact on the gut microbiome. Researchers observed a notable increase in median fecal microbiome -diversity (from 6.18 to 8.42) and a rise in the relative abundance of butyrate producers (RABP) (from a median of 0.03 to 0.08).
These findings are significant because a diverse gut microbiome and a higher prevalence of butyrate-producing bacteria are associated with improved metabolic health, reduced inflammation, and enhanced immune function—all factors implicated in the progression of plasma cell disorders. The negative correlation between -diversity and BMI, and positive correlations with fiber, HEI-2020 score, and dietary adherence, further underscore the direct link between dietary quality and gut health. Importantly, these positive changes were sustained at weeks 24 and 52, suggesting long-term benefits.
Francesca Castro emphasized the broader implications of these findings: “Our results highlight the importance of improved dietary quality in early disease states and could provide guidance for future clinical trials,” Castro said in a statement. This study represents a pioneering effort in exploring dietary interventions for hematologic malignancies and offers a promising non-pharmacological approach to potentially delay disease progression.
Impact on Black Patients with Multiple Myeloma
The implications of this research are particularly pertinent for Black patients, who experience a disproportionately higher burden of MGUS, SMM, and multiple myeloma. Black individuals have a two to threefold higher prevalence of MGUS compared to White individuals, and are diagnosed with multiple myeloma at twice the rate of White individuals, often at a younger age. While the rates of progression from MGUS to MM do not appear to differ significantly by race, the higher prevalence of the precursor condition in Black communities contributes directly to the increased incidence of MM.
Socioeconomic factors, access to healthcare, and genetic predispositions are all believed to play a role in these disparities. Furthermore, health conditions often associated with a sedentary lifestyle and a diet lacking in fiber, such as obesity and insulin resistance, are also more prevalent in some segments of the Black population, potentially exacerbating the risk of disease progression. The finding that a high-fiber plant-based diet can lead to significant reductions in BMI, improvements in insulin resistance, and modulation of the gut microbiome is especially relevant.
For healthcare professionals serving Black patient populations, these findings underscore the critical importance of early and culturally sensitive dietary counseling. Implementing HFPBD interventions could address modifiable risk factors that disproportionately affect Black patients, potentially mitigating the higher incidence and earlier onset of these precursor conditions. This dietary approach offers a tangible strategy for proactive management, empowering patients to take an active role in their health and potentially altering the trajectory of their disease. Future research should focus on larger, multi-center trials that include diverse patient populations to confirm these findings and develop tailored dietary interventions that address the unique needs and challenges faced by Black patients.