Could adding in plant-based meals help patients with multiple myeloma during transplant? A new study in Blood Advances from the Markey Lab in the Translational Science and Therapeutics Division suggests that eating plant-based, whole foods meals that are high in fiber and diverse nutrients may be a way to support the gut microbiome during treatment.
Maximum microbiome disruption during hematopoietic stem cell transplantation (HCT) usually occurs when white blood cell counts plummet in the stage called the neutropenic period, which is typically 7-14 days post-transplant. The magnitude of this disruption has previously been linked to increased disease progression and worse overall outcomes in a large, multi-center study.
Figuring out how to support the health of the microbiome for HCT patients is not easy. Even prior to treatment, patients with multiple myeloma often have a disrupted microbiome. Adding chemotherapy, the strong antibiotics that are administered for post-transplant fevers and infections, and the inevitable dietary changes that occur when people just aren’t feeling well tends to disrupt the gut microbiome even further.
To fix this microbiome disruption, we need to understand what makes a healthy gut microbiome in the first place. As I’ve written about before, that’s more complicated than it sounds. Overall diversity of species is thought to be a good start, but there’s more to it than that: ideally, there are high numbers of symbiotic species (also called commensal bacteria, or ‘normal gut flora’) and low numbers of pathogens (or pathobionts).
Some of the benefits of a robust, healthy microbiome may come from the microbial fermentation of complex fibers. These metabolic byproducts are called short-chain fatty acids (SCFAs), and they have been linked to lower levels of gut inflammation and enhanced anti-tumor immunity. In the lab, SCFAs can also directly inhibit cancer stem cell growth.
Unlike the typical “western diet,” which is high in refined sugars and processed foods, plant-based diets are higher in the fermentable fibers that promote SCFA production. The benefits of eating this high-fiber diet can start before a cancer diagnosis: there are markedly lower rates of multiple myeloma among vegans and vegetarians. Mouse models of multiple myeloma demonstrate that SCFA production may help slow disease progression. Additionally, studies in patients with myeloma precursor conditions found that switching to this kind of diet can improve intestinal diversity and ultimately, quality of life.
However, expecting cancer patients to radically change their diets during treatment is a big ask.
“Dietary studies in cancer patients are challenging to perform,” explains Dr. Kate Markey. However, given the possible benefits of adding in some plant-based meals during transplantation, she wondered: how feasible is it to ask our patients to add in plant-based meals to their diets during treatment?
To answer this question, the study team recruited 22 adult patients undergoing autologous HCT at Fred Hutch between 2024 and 2025 to receive pre-made meals for 5 weeks of treatment. Each patient was provided 3 meals per day plus snacks from a plant-based meal delivery service, starting at one week before the transplant to 28+ days post-transplant.
The meals were safe for immunocompromised patients and required minimal preparation (e.g. around 3 minutes in the microwave or around 5 minutes in a skillet). Meals were centered around plant-based protein sources such as tofu and included an array of cooked vegetables and grains and came from a company that also offers food delivery to the general population.
During the course of the study, patients met with the study dietitian – Kate Ueland – as well as the clinical dietitian team, led by Mary Rasmussen, and also recorded what they were eating for their meals. Patients were not restricted to eating only the provided meals or to stick to a purely plant-based diet. This is crucial because while the researchers wanted to encourage high-fiber plant-based eating, they didn’t want to restrict any foods while patients are not feeling well and may be wanting to reach for familiar ‘comfort’ foods rather than the unfamiliar study diet.
This flexibility had the added benefit of stratifying the cohort into two groups: those who ate a lot of the provided meals and those who were unable to eat as many of the meals.
The authors found that, overall, the provided plant-based dietary intervention was well-tolerated by many patients.
“This study demonstrates that it is feasible to ask patients who are going through very intense chemotherapy and recovery to make big changes to their usual dietary patterns,” says Dr. Markey.
The researchers also collected weekly stool samples to see whether eating more of the plant-based meals was associated with changes in their gut microbiomes. They observed some encouraging differences when the compared the microbiome samples between ‘higher’ consumers versus ‘low’ consumers.
“In the patients who were able to consume a high number of the delivered meals, we saw clear changes in the microbiome - with more ‘good guys’ maintained, and fewer thriving ‘bad guys,” explains Dr. Markey.
“We also measured higher concentrations of immunomodulatory short-chain fatty acids in stool at the end of the study window compared with the beginning,” she continues. “Our sample size was too small to demonstrate a dose-dependence there, but I’m hopeful we would observe that in a larger study.”
The authors are excited by their results, and they’re already starting to think about using plant-based dietary interventions for other patients.
“We are actively seeking funding to support a randomized study using plant-based diets as a strategy to support the microbiome during auto-HCT, and in the CAR T patient population,” says Dr. Markey.
This pilot is just the beginning of what the authors want to measure. For future work, they’re interested in including behavioral support to help patients consume more of what may be an unfamiliar diet. They also are excited to get more data points on functional microbiome changes.
Ultimately, the science of diet and microbiomes in cancer patients just needs a lot more research.
“Ideally we’ll be able to secure the grant funding to perform more research so we can generate high-quality evidence for the ideal diet during treatment,” concludes Dr. Markey.
In the meantime, researchers and doctors will do what they can to make cancer patients healthier and more comfortable during transplant.
Fred Hutch/University of Washington/Seattle Children’s Cancer Consortium Members Drs. Melinda Biernacki, Albert Yeh, Shivaprasad Manjappa, David Fredricks, Marie Bleakley, Leona Holmberg, Daniel Raftery, Jing Ma, Geoffrey Hill, Marian Neuhouser, Stephanie Lee, and Kate Markey contributed to this research.
The spotlighted research was funded largely by a grant from Swim Across America. The research team received a Scholar Award from the American Society of Hematology (ASH) and additional funding from the National Heart, Lung, and Blood Institute and the National Cancer Institute.
Ueland K, Elahi T, Rasmussen M, Wolfe AE, Purcell H, Chakka SR, Mirimo-Martinez M, Persinger H, Johnson K, Boynton AM, McMillen K, Byelykh M, Biernacki MA, Yeh AC, Ali N, Manjappa S, Wuliji N, Fredricks D, Bleakley M, Holmberg LA, Peled JU, Schenk J, Raftery D, Ma J, Hill GR, Neuhouser ML, Lee SJ, Markey KA. 2026. Plant-based whole-food diets are feasible during auto-HCT and are associated with dose-dependent microbiome modulation. Blood Adv. doi: 10.1182/bloodadvances.2026020270
Hannah Lewis is a postdoctoral research fellow with Jim Boonyaratanakornkit’s group in the Vaccine and Infectious Disease Division (VIDD). She is developing screens to find rare B cells that produce protective antibodies against human herpesviruses. She obtained her PhD in molecular and cellular biology from the University of Washington.