A new study eBioMedicine studied the effect of including canned navy beans into the normal diet for eight weeks.
This research focused on how such a dietary change affects the gut microbiota as well as circulating markers and metabolites in obese individuals with a history of colorectal neoplasia and precancerous polyps. The study also included participants taking medications such as statins or metformin.
Long-term follow-up of this low-risk, non-invasive study titled ‘Beans Enriching the Gut Microbiome and the Negative Effects of Obesity (BE GONE)’, conducted at MD Anderson Cancer Center in Texas, United States of America (USA), is ongoing.
To work: Modulating a prebiotic food source influences inflammation and immune-regulating gut microbes and metabolites: insights from the BE GONE trial. Image Credit: Michelle Lee Photography/Shutterstock.com
Background
Studies have shown that patients with obesity, unhealthy diets, and a history of colorectal cancer or precancerous polyps often experience long-term imbalances in their gut microbiomes, even after successful cancer treatment or polyp removal.
Adjusting the diet to alter the gut microbiome appears to be a promising strategy for the management of patients at high risk. However, a significant challenge is ensuring that these individuals, especially those recovering from cancer, can successfully adopt and tolerate dietary changes.
In this context, the small, white navy bean stands out. It is a nutrient-rich food that is both affordable and widely available. Acting as a prebiotic, navy beans may play an important role in restoring the diversity of the gut microbiome. This could potentially improve both the gut and metabolic health of cancer survivors.
A growing body of evidence suggests that these patients have intestinal dysbiosis due to metabolic dysbiosis in the production of branched-chain amino acids, increased intestinal permeability, and low-grade endotoxemia.
About the study
In the current study, researchers first subjected all enrollees to a four-week stabilization/acclimatization period, then were randomly divided into two groups.
The first group (control) consisted of participants following a normal diet that did not include dried beans, while the other group (test) began an eight-week intervention diet.
The intervention diet involved slowly adding navy beans to participants’ normal diet (1 cup/day) over eight weeks and supplementing with 16 g dietary fiber, 14 g protein, and 220 kcal.
This was followed by immediate switching to the control diet, which facilitated cross-arm comparison of changes in stool and blood markers every four weeks throughout the eight-week intervention to measure adherence throughout the intervention period.
The primary outcome was intra- and intra-individual changes in the gut microbiome during the intervention. Specifically, they assessed gut microbial alpha diversity, relative abundance of individual taxa, and beta diversity distances from 16S ribosomal ribonucleic acid (rRNA) gene profiles for each subject at each time point.
The researchers also evaluated the stability of these measures during the “return to control” and “stay in control” periods.
Additionally, the researchers performed a global metabolomic analysis in parallel to identify changes in circulating metabolites (proteomic biomarkers) associated with the intervention and changes in microbial composition.
Results
The study began with initial contact with 240 people, of whom 71 consented to participate. Ultimately, 69 people participated in the 16-week trial and the completion rate was 87%. Of these, 48 participants were included in the intention-to-treat (ITT) analysis.
The study observed that the eight-week intervention led to a slight increase in fiber consumption for most participants who had dietary fiber intake below the recommended threshold at baseline.
Although some participants reported experiencing mild to moderate bloating and changes in bowel habits, overall compliance with the dietary intervention prescribed in the study was high.
In particular, those who experienced changes in their bowel habits also saw an increase in the diversity of their gut microbiomes during the intervention period.
A linear mixed model analyzing temporal changes in microbial taxa showed that some bacterial taxa decreased post-diet intervention, while others increased, with more significant changes in alpha and beta diversity in older participants.
Interestingly, some of the bacteria that changed upon intervention were sulfur-metabolizing species (e.g. bilophila wadsworthia) has been linked to colorectal cancer.
Shotgun metagenomic sequencing of 140 samples from 48 participants confirmed the consistency of these results.
It also demonstrated how prebiotic dry bean intervention downregulated microbial gene content pathways associated with branched-chain amino acid biosynthesis and fermentation. Metagenomic sequencing also revealed increases. Eubacterium rectal And Bifidobacterium adolescentisalis species.
The study intervention increased inverse Simpson index scores, an indicator of microbial alpha diversity, indicating a more balanced distribution of all bacterial species.
relative abundance roseburia And Streptococcus rejected at this time fecalibacteria rose.
Regarding the effects on the host metabolome, pipecolic acid (PA) and S-(5′-Adenosyl)-1-methionine (SAM) increased, while indole derivative decreased during the intervention.
Similarly, trigoneline and theophylline increased during intervention but remained unchanged when participants went to control. Additionally, the “dose” of beans was sufficient to improve LDL and overall metabolic health.
Furthermore, bean intervention led to an increase in fibroblast growth factor (FGF-19), a decrease in the levels of several other immuno-oncology cytokines such as interleukin ten receptor alpha (IL10ra) and programmed cell death 1 ligand 1. (PD-L1). All these microbial metabolites and biomarkers have potential therapeutic significance.
Results
This trial showed that adding a cup of prebiotic beans to the regular diet is a safe and scalable strategy to modulate the gut microbiome of colorectal cancer patients who may not be able to comfortably sustain other dramatic changes without support.
In fact, prebiotic foods also show the potential to be an important component of adjunctive nutritional regimens for patients with inflammatory bowel disease and diabetes.
Future research should advance the understanding of metabolites and biomarkers that may complement this nutritional strategy and improve clinically meaningful outcomes obtained with prebiotic foods.