A recent study on the effect of resistant starch consumption on the risk for colorectal cancer found that consuming 40g of resistant starch with a diet high in red meat can reduce the risk of colorectal cancer associated with a diet high in red meat(1). The researchers took 23 subjects and had them follow either a high meat diet or a high meat diet coupled with 40g of resistant starch for 4 weeks. They then measured the expression of colorectal cancer promoting genes. When the subjects consumed a high red meat diet, expression levels of the genes increased by 30%. When the subjects consumed 40g of resistant starch with a high meat diet, expression levels of the genes went back to normal.
The researchers believe the improved effect of resistant starch is due to the presence of butyrate in the colons of people consuming resistant starch. Resistant starch is a form of fiber that escapes human digestion and becomes available to bacteria in the colon. Butyrate is a byproduct of the fermentation of resistant starch by resident bacteria. While high consumption of meat increases expression of the genes associated with colorectal cancer, consuming resistant starch effectively reversed this expression, possibly by increasing levels of butyrate and other beneficial short chain fatty acids(SCFAs).
Good sources of resistant starch are under-ripe/green bananas and plantains, cooked and cooled potatoes(at least 24 hours), and chemically altered food products such as Hi-maize, a modified cornstarch currently used as a substitute for flour in home baking. Bob's Red Mill Unmodified Potato Starch is also a good source of resistant starch at 8g/tablespoon. While many have taken to huge servings of a single source, getting multiple types of fiber/resistant starch is likely a better option as different bacteria in different areas of the digestive tract ferment different types of fiber in to butyrate and other SCFAs.