‘Adding a cup of beans’ to diet boosts gut microbiome diversity in high-risk obesity, CRC (2024)

Key takeaways:

• Daily consumption of 1 cup of beans improved gut microbiome diversity and composition within 8 weeks.
• A return to the usual diet without beans resulted in reversal in positive changes in bacteria within 8 weeks.

Adding one cup of navy beans to the usual diet of individuals with obesity and a history of colorectal cancer improved gut microbiome diversity and regulated metabolites and markers related to disease, according to research in eBioMedicine.

“From a nutritional perspective, beans contain multiple dietary components that are known to stimulate the microbiome,” Carrie Daniel-MacDougall, PhD, associate professor of epidemiology at the University of Texas MD Anderson Cancer Center, told Healio. “Beyond their potential as highly effective prebiotic food, there is strong and consistent evidence supporting beans as part of a healthy diet for the prevention of cardiovascular disease and cancer, particularly colorectal cancer. However, most Americans are not excited by the idea of eating beans and they are particularly avoided by individuals with digestive issues, who might be the most likely to benefit.”

Daniel-MacDougall continued: “It was also not clear whether simply adding beans to a not-so-healthy diet, which comes in many forms, would be enough to have a positive impact on high-risk patients.”

MacDougal and colleagues conducted Beans to Enrich the Gut microbiome vs. Obesity’s Negative Effects (BE GONE), a low-risk, noninvasive, dietary intervention trial to investigate the effect of navy bean consumption on gut microbiota, metabolites and immune and inflammatory biomarkers.

They enrolled 55 patients with obesity and a history of CRC, who participated in a 4-week equilibration and then continued with their usual diet without beans (control, n = 29) or added one daily cup of study beans to their usual diet (intervention, n = 26) with crossover at 8 weeks.

Researchers collected stool and fasting blood samples every 4 weeks to assess the primary outcome of intra- and inter-individual changes in the gut microbiome as well as circulating markers and metabolites.

According to results, 87% of participants completed the full 16-week trial, of whom 75% had a history of CRC and 25% had a history of precancerous polyps. There was an increase on-intervention in microbial alpha diversity within 8 weeks among the whole population (linear mixed effect [LME] = 0.16; 95% CI, 0.02-0.3) with shifts in multiple bacteria indicative of prebiotic efficacy.

“Adding a cup of beans to the usual diet with no other changes in lifestyle, was sufficient to increase the diversity of the gut microbiome and support bacteria that maintain gut health and host health, while competitively reducing resources for opportunistic pathogens,” Daniel-MacDougall said. “This was further supported by our findings for circulating blood metabolites, immune and anti-inflammatory markers.”

Researchers also performed analysis of genus-level bacteria found in at least 80% of participants, which showed the on-intervention intra-patient relative abundance of Roseburia (LME = –0.49; 95% CI, –0.86 to –0.13) and Streptococcus (LME = –0.48; 95% CI, –0.92 to –0.04) decreased at the 4-week midpoint, while the relative abundance of Faecalibacterium (LME = 0.4; 95% CI, 0.02-0.78) increased within 8 weeks.

In addition, Streptococcus, Collinsella, Escherichia, Ruminoccocus torques, Fournierella, Oscillibacter and another member of the Oscillospiraceae family decreased after the intervention, while Odoribacter, Bifidobacterium, Eubacterium siraeum, Eubacterium brachy and other members of Ruminoccocus and Lachnospiraceae families increased.

“Another striking finding was that within 4 to 8 weeks of returning to the usual diet without beans, many of these benefits were lost,” Daniel-MacDougall told Healio. “From a scientific perspective, it supported that what we saw was directly related to the simple bean intervention. From a patient or clinical perspective, it really reinforced that modest but effective diet changes need to be sustained, and if left unsupported, how rapid the effect of ‘diet decline’ in a patient could be.”

Further, the circulating metabolome demonstrated parallel shifts in nutrient and microbiome-derived metabolites, namely increased pipecolic acid and decreased indole, which regressed following the intervention. Researchers noted “no significant changes” in circulating lipoproteins within 8 weeks, although there were changes in proteomic biomarkers of intestinal and systemic inflammatory response.

“The microbiome is very responsive to diet and to prebiotic foods,” Daniel-MacDougal said. “We need to continue to work to understand the best strategies for every patient, as well as specific conditions. At the end of the day, every patient must eat and will have to make food choices. If we can understand the microbiome and how to support or ‘treat’ it with diet, this can be a very important tool and effective health ally alongside other clinical interventions.”