High-Fiber Diet Linked to Improved Stem Cell Transplant, GvHD Outcomes

SAN DIEGO — Recipients of allogeneic hematopoietic cell transplantation (allo-HCT) for blood disorders who maintain diets high in fiber show significant improvements in overall survival and a reduced risk of developing the potentially life-threatening complication of acute graft-versus-host disease (aGVHD), new research shows.

Importantly, the findings suggest standard recommendations for patients of a low-fiber diet following allo-HCT may run counter to the potential benefits. 

“Significant decrease of fiber intake during transplantation is detrimental. It’s a lost opportunity to promote a healthy gut microbiome, recover from treatment-related microbiota injury, and protect against GVHD,” said first author Jenny Paredes, PhD, a staff scientist at City of Hope National Medical Center in Duarte, California, in a press statement for the study presented here at the American Society of Hematology (ASH) 2024 Annual Meeting.

Although the health benefits of dietary fiber on the gut microbiome are well-documented, the effects have recently been shown to extend to outcomes after allo-HCT in general, with  researchers finding increased overall survival when there is higher diversity in the gut microbiome, including a higher abundance of butyrate producers and lower abundance of enterococcus, explained Paredes when presenting the findings.

Acute GvHD, a common and potentially life-threatening complication of allo-HCT, can have symptoms that mimic irritable bowel disease (IBD), including abdominal pain or cramps, nausea, vomiting, and diarrhea. The low-fiber diet recommendations, including avoidance of raw vegetables and fruits before and after the allo-HCT procedure, are designed to counter those effects, as well as reduce exposure to bacteria.

However, with data suggesting the potential benefits of dietary fiber could extend to the prevention of GvHD, Paredes and colleagues further investigated.

For the observational study, they evaluated all dietary data on 173 allo-HCT recipients at Memorial Sloan Kettering Cancer Center (MSKCC) from 10 days prior to transplantation to 30 days post-transplantation, representing 3837 patient-days in total.

Data collected from the patients also included rRNA sequencing of fecal samples and fecal short-chain fatty acid concentration. 

Participants had a median age of 60, and 45% were female. The most common diseases being treated were leukemia (50%), myelodysplastic syndrome (25%), and non-Hodgkin’s lymphoma (8.7%).

After stratifying patients based on high- or low-fiber intake, those with high-fiber intake were found to have significantly higher rates of microbial α-diversity (P = .009), a higher abundance of butyrate producers (P = .03), and a higher concentration of butyrate (P = .02), a short-chain fatty acid that plays a key role in gut health. 

Furthermore, the high-fiber group had significantly higher overall survival in an analysis extending to 24 months relative to day 12 of the study (P = .04).

Focusing on GvHD outcomes, the authors further evaluated data on 101 non-T-cell–depleted patients, and identified 29 patients without GvHD and 24 who developed lower gastrointestinal (GI) GvHD. 

Patients with lower GI GvHD had significantly lower fecal concentrations of butyrate (P = .03) and acetate (P = .02).

However, patients among those in the high-fiber intake group had a significantly lower cumulative incidence of developing GvHD at day 100 (P = .034) and a lower incidence of lower GI GvHD (P = .04).

A separate preclinical analysis of a mouse model with GvHD further showed that a fiber-rich diet (12% cellulose) significantly increased the expression of genes associated with reduced GvHD, including IDO1 and CEACAM1, and those associated with enrichment of the bile acid pathway.

The findings suggest an opportunity to improve outcomes with relatively small dietary changes, Paredes said.

“Strategies to increase the fiber concentration in these diets paired with the safety that these patients need is what makes this study exciting,” she said in an interview. 

“Increasing the fiber intake by 10 to 20 grams/day, could potentially increase the microbiome diversity and abundance of butyrate producers, which have been correlated with higher overall survival rates post allo-HCT,” she continued.

“[For instance], that could be an avocado per day, or it could be a small salad per day, or a small vegetable soup per day,” she added. “I would encourage institutions to re-evaluate their menu planning and see how to include more fiber into the meals in a safe way.”

Ultimately, “I think that a dietary intervention outweighs the risks of a pharmacological intervention,” Paredes added.

The necessary duration of a high-fiber diet to produce the beneficial effects on allo-HCT outcomes would likely be over the course of the pre- and post-transplant periods, Paredes added.

“With the survival analysis extending from 5 days before transplantation to 12 days post, we are looking at an intervention that potentially could be around 20 days,” she said.

“We would love to take advantage of the pretransplantation window, in particular, and we can see that just increasing the fiber intake by about 20 grams during this window was shown to improve overall survival after 24 months,” Paredes added.

Importantly, however, some patients may not be appropriate for higher-fiber dietary changes, Paredes cautioned. 

“Patients that have developed IBD-like symptoms and severe GvHD patients, for example, or with lower GI-GvHD grades 3 and 4 would be not appropriate candidates for a high-fiber diet,” she said. 

High-Fiber Diet Slows MM Disease Progression?

The potential important benefits of a high-fiber diet in blood diseases were further demonstrated in a separate study also by MSKCC researchers presented at the meeting, which showed encouraging signs that a plant-based diet rich in fiber could potentially slow disease progression in multiple myeloma (MM).

NUTRIVENTION included 20 patients with the two precancerous MM conditions, monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM), which can last for years without progressing to MM, and which researchers have speculated could be a potential opportunity to intervene to prevent progression to cancer.

Patients were provided with a 12-week controlled diet plus health coaching for another 3 months; no meals or coaching were provided for the rest the 1-year study period. Participants had a median age of 62 and, with being overweight/obesity a risk factor for MM, had a body mass index (BMI) of 25 kg/m² or higher.

The trial met its endpoint of feasibility, with 91% adherence in the first 3 months. The rate of consumption of unprocessed plant foods increased from 20% at baseline to 92% on the intervention. Overall adherence was 58%. Insulin and anti-inflammatory markers also improved and, despite no calorie restriction, there was a 7% sustained reduction in BMI. 

Notably, two patients in the study had stabilization of disease progression.

“We saw improvements in all spheres, including metabolism, microbiome, and immune system markers, and we also saw that two patients with progressive disease had the progression stabilize and slow down on the intervention,” said principal investigator Urvi A. Shah, MD, in a press statement. 

“Even though it’s just two cases, to our knowledge, it has not been shown before in an intervention setting that you can improve diet and lifestyle and actually slow or change trajectory of the disease,” she noted.

The researchers caution that findings in mice do not necessarily translate to humans but note another experiment in mice with SMM that showed animals fed a normal diet had progression to MM after a median of 12 weeks, compared with a median of 30 weeks among those fed a high-fiber diet.

Notably, all mice in the normal-diet group progressed to MM, whereas 40% of mice in the high-fiber group did not. 

“We found that a high-fiber plant-based diet can improve BMI, improve insulin resistance [and] the microbiome through diversity and butyrate producers, and with the production of short-chain fatty acids, can have effects on inflammation, immunity, innate and adaptive antitumor immunity, and tumor cells or plasma cells,” said Shah during her presentation.

The study was supported by funding from the National Cancer Institute and private foundations. Paredes has reported no relevant financial relationships. Shah has reported relationships with Sanofi, Bristol Myers Squibb, and Janssen.