A high-fiber, plant-based diet may play a key role in improving health outcomes for individuals diagnosed with early-stage blood cancers such as monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM), according to new research presented at NUTRITION 2025, the annual meeting of the American Society for Nutrition.

The study, led by Francesca Castro, R.D., of Memorial Sloan Kettering Cancer Center, focused on whether a structured dietary change could positively impact the gut microbiome and disease markers in patients with MGUS and SMM—conditions that often precede the development of full-blown multiple myeloma.

Over the course of a 12-week intervention, 20 overweight or obese patients followed a high-fiber plant-based diet (HFPBD) along with behavioral counseling support over a total of 24 weeks. The findings showed that the diet was not only safe and feasible but also significantly improved several key health indicators, including body mass index (BMI), gut microbiome diversity, and overall diet quality.

Participants saw their median dietary adherence skyrocket from 20 percent at baseline to 91 percent by week 12. Median BMI decreased by 6.6 percent, and daily fiber intake nearly doubled. Notably, the Healthy Eating Index (HEI)-2020 score rose from 61.4 to 80, indicating a substantial improvement in diet quality.

Additionally, researchers found that the gut microbiome of participants became more diverse and healthier, with an increased presence of butyrate-producing bacteria—beneficial microbes associated with reduced inflammation and improved metabolic health. These microbiome improvements were positively linked to higher fiber intake and dietary adherence, and inversely related to BMI.

The encouraging results were sustained at 24 and 52 weeks, suggesting lasting benefits of the diet intervention even beyond the active study period.

“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.

As multiple myeloma remains incurable and early detection and intervention are critical, the study adds to growing evidence that nutrition can be a powerful tool in managing cancer risk and progression—especially when leveraged in the early, precancerous stages. Further trials are expected to explore how such dietary changes could slow or even prevent the transition from MGUS and SMM to active multiple myeloma.