Plant-based dietary strategies may offer a tractable approach to mitigating microbiome disruption and improving outcomes in patients undergoing autologous hematopoietic cell transplantation (auto-HCT) for multiple myeloma, a population in whom intestinal dysbiosis has been linked to infectious complications and inferior survival. We conducted a single-arm study to test the feasibility and biological activity of a high-fiber, plant-based, whole-food meal delivery intervention during the peri-transplant period. Adults with multiple myeloma (n = 22) received fully prepared, plant-based meals for 5 weeks spanning conditioning, neutropenia, and early recovery, with the goal of supporting consumption of nutrient-dense, high-fiber foods despite transplant-related symptoms that often limit oral intake. The primary endpoints were feasibility and tolerability, defined by successful enrollment, adherence to study procedures, and patient-reported intake of study meals; diet was quantified using prospective food diaries and 24-hour dietary recall surveys. Secondary endpoints included changes in gut microbiome composition and function assessed by shotgun metagenomic sequencing and stool short-chain fatty acid (SCFA) measurements.

The intervention was feasible and generally well tolerated, with all participants consuming at least some proportion of delivered meals and with adherence sufficient to support planned dietary and correlative analyses. Greater intake of study meals was associated with more pronounced shifts in gut microbial communities, including enrichment of SCFA-producing taxa and compositional changes consistent with a fiber-responsive microbiome. Stool SCFA concentrations increased from baseline to the end of the intervention, suggesting a functional impact of the dietary strategy on microbial metabolite production during the peri-transplant period. These findings demonstrate that a plant-based meal delivery intervention is implementable during auto-HCT and suggest dose-dependent modulation of the gut microbiome and its metabolic output. Larger randomized trials are warranted to determine whether microbiome-targeted nutrition can reduce transplant-related toxicities, enhance immune recovery, and improve disease control in multiple myeloma. The trial is registered at ClinicalTrials.gov (NCT06559709).

MAR reports consulting with Johnson and Johnson. NW is on the advisory board for Mustang Bio. KAM holds equity in PostBiotics Plus and has previously consulted for Incyte and Crestone. The study did not receive sponsorship or funding from the meal-delivery company Thistle, meals were purchased using independent study funds.

NCT06559709

This study was funded by Swim Across America, by a grant awarded to KAM. We wish to acknowledge the support of the Cancer Center Support Grant to the Fred Hutchinson Cancer Center (P30 CA015704-50). ACY acknowledges funding from the ASH Scholar Award and the NIH K08 HL167161.

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The IRB of the Fred Hutchinson Cancer Center gave full ethical approval for this work.

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Funding: This study was funded by Swim Across America, by a grant awarded to KAM. We wish to acknowledge the support of the Cancer Center Support Grant to the Fred Hutchinson Cancer Center (P30 CA015704-50). ACY acknowledges funding from the ASH Scholar Award and the NIH K08 HL167161.

Presentations: This work has not been shared in any meetings.

Disclaimers: None.

All data produced in the present study are available upon reasonable request to the authors and sequencing and metabolomic data will be made publically available within the appropriate NIH databases at the time of formal publication.