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Resistant starch reduces colorectal cancer risks associated with a high-red meat diet.

Colorectal cancer is the third most common cancer worldwide. Robust evidence suggests that red meat consumption markedly increases a person’s risk of developing colorectal cancer.. Findings from a 2014 study suggest that resistant starch consumption alters microRNA expression, potentially moderating the cancer risks associated with red meat consumption.

Resistant starch is a type of carbohydrate that resists digestion in the small intestine. Instead, resistant starch undergoes microbial fermentation in the colon, providing nutrients for the microbes and producing butyrate, a short-chain fatty acid that supports the health of colonocytes – the cells that line the colon and rectum (the end portion of the colon). Foods that contain resistant starch include breads, pasta, legumes, nuts, seeds, bananas, and starchy vegetables, such as potatoes. Cooking and preparation techniques alter resistant starch content in foods, however. For example, a study found that a 3-ounce portion of baked potatoes typically provides 3.6 grams of resistant starch, but a similar portion of boiled potatoes provides just 2.4 grams.

MicroRNAs are single-stranded RNA molecules that play roles in the regulation of gene expression. They calibrate as much as 30 percent of mammalian protein-encoding genes. MicroRNA expression is typically dysregulated in the setting of cancer. However, evidence from an in vitro study suggests that butyrate modulates microRNA expression in colorectal cancer cells.

The study involved 23 healthy adults between the ages of 50 and 75 years old. Each participant followed two four-week-long dietary interventions (separated by a washout diet): a high-red meat diet (providing 300 grams of red meat daily – about three-fourths of a pound) and a high-red meat diet that also provided 40 grams of butyrylated resistant starch, a chemically modified form of resistant starch that is an effective vehicle for delivering butyrate to the colon. The investigators collected rectal tissue samples via biopsy at the completion of each intervention diet.

After completing the high-red meat diet, the participants' rectal tissues exhibited a 30 percent increase in a cluster of microRNAs called microRNA 17-92, which participates in the cell cycle, proliferation, apoptosis (cell death), and other processes involved in cancer. But when the participants added resistant starch to their high-red meat diet, their microRNA 17-92 levels returned to baseline levels.

These findings suggest that butyrylated resistant starch moderates the cancer-promoting effects of a diet high in red meat. Some of this benefit may arise from the delivery of butyrate. Learn more about butyrate in our overview article.

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