Traditionally, the humble bean doesn’t have the best reputation when it comes to its impact on the gut. However, study with colorectal cancer survivors showed that certain legumes could offer a swift, significant benefit to gut health, modulating markers linked to disease and obesity.
The MD Anderson Cancer Center study followed 48 men and women who met the prerequisites of obesity and bowel lesions, with a history of colorectal cancer (CRC) or precancerous polyps, for 16 weeks as they incorporated a cup of dry navy beans (Phaseolus vulgaris) into their daily diet.
These small white legumes are the ones you'll most likely find swimming in sauce in a can of baked beans. Researchers focused on these beans because of their high fiber content, amino acids and other nutrients that can boost beneficial bacteria in the colon.
Analysis of blood and stool samples taken throughout and following the study revealed a swift and significant change in gut health across the board, notably with an increase in the population of beneficial bacteria (Faecalibacterium, Eubacterium and Bifidobacterium species) and a decrease in pathogenic bacteria.
These opportunistic bacteria can go on attack when they sense a weakened immune system and have been linked to exacerbating chronic diseases such as inflammatory bowel disease and cancer.
Certain species of gut bacteria have already been implicated in an increased risk of CRC.
"Observing a shift in microbiome diversity with diet intervention alone is rare, and this study underscores the ability of a readily available prebiotic food to bring about such changes," said co-author Dr Carrie Daniel-MacDougall, associate professor of epidemiology. "Over the course of eight weeks, there was an improvement in participants' gut health, marked by an increase in beneficial bacteria, which wards off the harmful bacteria."
The trial, named BE GONE (Beans to Enrich the Gut microbiome vs. Obesity’s Negative Effects), saw participants provided with a cup a day of dry, pre-cooked navy beans that could easily be incorporated into meals. People prepared their own meals and were considered adherent to the guidelines if they consumed at least 80% of the daily requirement. Every four weeks, stool and fasting blood samples were taken to assess any shifts in the gut microbiome.
Studying this cohort was of particular interest for the Cancer Center. While obesity, a poor diet or other gastrointestinal conditions can upset a balanced gut microbiome, it can lead to worse outcomes for people in recovery. Gut inflammation spurred on by a poor diet can undermine prevention efforts following removal of precancerous polyps or cancer treatment and even impact survival.
Notably, when the participants returned to their pre-study diet, without the cup of beans per day, their gut health and population of healthy bacteria diminished within four weeks.
"The beans did not appear to induce gut inflammation or seriously impact bowel habits, which is crucial for CRC survivors and patients," said Daniel-MacDougall. "However, once participants stopped eating the beans, the positive effects faded quickly, highlighting the need to educate patients on how to maintain healthy habits."
Beans are often avoided due to anticipated gastrointestinal side effects – most commonly, bloating and flatulence. The side effects stem from the fermentation of the legumes' non-digestible oligosaccharides (fiber), which takes place in the colon and actually results in a boost of beneficial bacteria.
This latest study highlights how an accessible, prebiotic-rich food source can have a rapid impact on the health of the gut – and not just in patients at a higher risk of cancer-related inflammation. However, the researchers also point out that anyone with prior gut health issues should consult their physician before undertaking any substantial dietary changes.
The researchers will now look into a wider variety of prebiotics can benefit the microbiome of patients undergoing immunotherapy.
The study was published in the journal eBioMedicine.
Source: MD Anderson Cancer Center