Pam Harrison

April 07, 2017

A controlled dietary intervention aimed at increasing dietary fiber through the addition of rice bran (RB) and navy bean (NB) powder to meals and snacks alters gut microbiota in a way that might reduce the risk for colorectal cancer (CRC), suggests new research presented during the American Association for Cancer Research (AACR) 2017 Annual Meeting.

"Dietary rice brain and navy beans are examples of foods with high dietary fiber content and other important phytochemicals that have inhibited colon carcinogenesis in animal and human epidemiological studies," lead author Erica Borresen, MPH, Colorado State University, Fort Collins, states in her abstract.

"Our pilot findings warrant further evaluation of these specific foods in a larger cohort and for a longer duration of consumption to assess CRC control and prevention markers in colon tissue."

The pilot project was part of the Beans/Bran Enriching Nutritional Eating for Intestinal Health trials (BENEFIT) trial, which aims to boost community knowledge about how simple foods such as rice bran and beans can affect gut health.

Researchers recruited 29 CRC survivors and randomly allocated them to receive either 4 weeks of a diet that included 30 g of rice bran and 35 g of navy been power a day or a control diet containing neither of these foods. Rice bran is the part of the rice that is removed by polishing during processing. The rice bran and the navy bean powder were provided in both meals and snacks.

"Fasting blood, urine, and stool were collected at baseline, 2-week, and 4-week time points," the study authors write. "And the amount of RB or NB consumed (ranging from 4% to 9% of daily caloric intake) led to increased dietary fiber, iron, zinc, thiamine, niacin, vitamin B6, folate and alpha-tocopherol intake," they add.

Significant increases in several species of bacteria were detected in the stool microbiome of participants who were assigned to the supplemented diet in comparison with those assigned to the control group.

These included Methanobrevibacter, Paraprevotella, Ruminococcus, and Bifidobacterium species.

In the supplemented diet group, the stool microbiome demonstrated increased bacterial richness and diversity in comparison with the stool microbiome of the control persons.

"Plasma, urine, and stool metabolome changes revealed increases in a number of microbial, host, and diet-derived metabolites, such as phytosterols, fatty acids, amino acids, bile acids, and small molecular byproducts of carbohydrate metabolism," researchers add.

With respect to CRC prevention, growth of CRC cells was reduced in stool metabolite extracts 4 weeks after participants had received the diet supplemented with fiber in comparison with baseline.

"These results support dietary RB or NB modulation of metabolism from digestion, microbiota, and microbial biotransformation," the investigators conclude.

Not Enough to Eat "Once in a While"

Coinvestigator Elizabeth Ryan, PhD, College of Veterinary Medicine and Biomedical Sciences at Colorado State University in Fort Collins, had previously established that eating half a cup of beans together with 30 g of rice bran a day is sufficient to cause changes in small molecules that confer protection against CRC.

However, how to convince people to eat adequate amounts of these foods every day remains a challenge.

"It's not enough to say, 'I eat them once in a while.' That's not going to work, particularly if you are at higher risk [for CRC]," Dr Ryan said in a statement.

"You have to meet a dose. Just like you need a dose of a certain drug, you need to reach intake levels and consume increased amounts of these foods, and that's where people, including me, are challenged. Not everyone wants to open up a can of beans and eat them every day," she added.

Dr Ryan does feel it is feasible, provided the food industry is willing to make rice bran and bean powders available in commercial foods.

"Why not have rice bran and bean-based doughs and soups available to buy ready made so people can meet these nutritional recommendations?" she asked.

"I really feel there's hope in this being a practical solution to improve gut health and specifically colorectal cancer prevention," Dr Ryan concluded.

Guidelines from the American Institute for Cancer Research recommend that individuals consume more fruits, vegetables, whole grains, and legumes, such as beans, to reduce cancer risk.

The researchers have disclosed no relevant financial relationships.

American Association for Cancer Research (AACR) 2017 Annual Meeting. Abstract CT138/19, presented April 4, 2017.

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