Increasing evidence has shown that diet, obesity, and the gut microbiome (the resident microbial community) influence colorectal cancer risk. Reducing the risk of developing recurrent or new cancers is a heightened concern for colorectal cancer survivors, but studies of diet and the microbiome have not focused on this specific population. To inform recommendations for colorectal cancer survivors, an innovative clinical trial is focusing on a diet modification—the addition of navy beans—and its effect on the gut microbiome.
“We and others have shown that poor diet, obesity, and associated inflammatory and metabolic conditions significantly contribute to disease recurrence and mortality in colorectal cancer survivors,” said Carrie Daniel-MacDougall, Ph.D., an assistant professor in the Department of Epidemiology at The University of Texas MD Anderson Cancer Center. Dr. Daniel-MacDougall is the principal investigator of a clinical trial in which beans are added to the diet of overweight or obese colorectal cancer survivors in hopes of enhancing their gut microbiomes and improving their metabolic health to lower their risk of cancer and other obesity-related conditions.
Strong research base
Beans were chosen for the intervention because decades of published research suggest they can reduce colorectal cancer risk. In the early 1990s, the National Cancer Institute’s Polyp Prevention Trial found that participants in the highest quartile of dry bean consumption had a reduced risk of adenoma recurrence. Laboratory investigations in ensuing years showed that beans prevented colorectal carcinogenesis in obese mice by inhibiting inflammatory mechanisms.
“Beans are high in protein and fiber. Fiber is integral to fostering a commensal, or protective, microbiome, which is important for cancer risk,” Dr. Daniel-MacDougall said. “Beans also have high levels of antioxidants and phytochemicals. They’re a natural prebiotic. And they’ve been established in cardiovascular research to improve cholesterol panels.”
Dr. Daniel-MacDougall chose navy beans for her clinical trial because they are low in the compounds that cause gas; they do not have a strong taste or color, so they can be incorporated easily with other foods; and most people do not eat them frequently, so it will be easier to see the specific effect of adding them to the diet. The pilot phase of the Beans to Enrich the Gut Microbiome vs. Obesity’s Negative Effects Trial (BE GONE, No. 2016-0365) enrolled 20 patients with adenomatous polyps. Analysis of the results is under way.
Now the trial’s second phase has begun enrolling overweight or obese adults with a history of colorectal cancer who have completed active treatment and have normalized bowel habits. Participants cannot have undergone resections of certain portions of the colon or have dietary restrictions that would preclude consumption of beans.
The trial uses a crossover design in which each participant serves as his or her own control. During the 8-week control period, participants eat their regular diet. During the 8-week intervention period, navy beans are added to the regular diet (beginning gradually and working up to 1 cup a day). A registered dietician and the Division of Cancer Prevention and Population Sciences’ Bionutrition Research Core provide support.
During the study period, participants have blood drawn five times and provide seven stool samples. The primary outcomes to be assessed are intra- and inter-individual changes in stool 16S rRNA profiles and blood metabolites. The relationship between changes in the gut microbiome and changes in host biomarkers—including established fecal surrogates of gut inflammation and integrity, circulating adipocytokines, and a comprehensive blood lipid and metabolic panel—will also be studied. In addition, the study team will assess the effect of participants’ baseline diet and microbiome on their biological response to the bean intervention.
“People want to know: ‘What’s the one thing I can eat to improve my microbiome?’ or ‘What’s the one thing I can eat to lower my cancer risk?’” Dr. Daniel-MacDougall said. “If our research confirms an impact, it’d be easy to say, ‘Just eat more beans.’”
For more information, contact Dr. Carrie Daniel-MacDougall at 713-563-5783. For more information about the BE GONE trial, email BEGONE@ mdanderson.org or visit www.clinicaltrials.org and search for study No. 2016-0365.
OncoLog, May-June 2018, Volume 63, Issue 5-6