Resistant starch contributes to digestive health in numerous ways:
- It feeds the beneficial bacteria, while suppressing harmful bacteria. This may be the mechanism by which many metabolic benefits are delivered – shifting bacteria composition within the gut, which in turn, impact the expression of hundreds of genes located within the gut. One organism, Ruminococcus bromii, appears to be a keystone species for bacterial breakdown (fermentation) of resistant starch. It is the initial organism that breaks down the resistant starch, producing particles that feed other organisms. People who eat resistant starch have significantly increased Ruminococcus bromii (i.e., a 2014 study by Harry Flint et al. at Rowett Institute of Nutrition and Health and a 2011 study by Dr. Guy Abell et al. at CSIRO Human Nutrition)
, while individuals lacking this species in their gut tend to be non-responders (also shown by Harry Flint et al. in 2012). Many other bacteria are increased as many aspects of the microbiome can shift after consumption of resistant starch (shown by Dr. Stephen O’Keefe et al. from the University of Pittsburgh in a 2015 diet swap study and by Dr. Jens Walters et al. from the University of Nebraska in 2010). - It reduces intestinal pH, which is a major biomarker for colon health: Phillips AJCN 1995, Noakes AJCN 1996, and Muir AJCN 2004.
- It increases the production of short-chain fatty acids, which are also a major biomarker for colon health: Phillips AJCN 1995, Jenkins JACN 1998, and McOrist JN 2011.
- It reduces the production of ammonia and phenols, which are believed to be harmful: Birkett AJCN 1996.
- It promotes regularity with a mild laxative effect. It increases bulking about 1.1 gram for each gram of resistant starch consumed, which is primarily increased bacterial mass. (In contrast, wheat bran increases bulking about 4 grams for each gram of fiber consumed, but its mass is primarily fiber and water.) In addition, genes within the large intestine are activated that assist with muscular contractions, which assist in maintaining regularity. Cassettari JP 2017
- It reduces diarrhea when given to adults and children with diarrhea-producing diseases, such as cholera and rotavirus: Ramakrishna NEJM 2000, Raghupathy JPGN 2006, Ramakrishna PO 2008. and Alvarez-Acosta JACN 2009.
- It reduced intestinal inflammation in American adults after two weeks on a diet rich in resistant starch. Reciprocally, when resistant starch was reduced in South Africans used to high levels of resistant starch, inflammation was significantly increased. O’Keefe NC 2015.
- It increased disposal of toxic nitrogen compounds (particularly indoxyl sulfate and p-cresol sulfate), in individuals with impaired kidney function. Sirich CJASN 2014
- Resistant starch reduced certain types of cancer (but not colorectal cancer) in a trial with almost 900 people with Lynch syndrome (a genetic variant with higher risk of developing cancer). The benefit was particularly pronounced for cancers of the upper GI tract (including pancreatic, bile duct, stomach and duodenal cancers). People consumed resistant starch for two years and were followed for more than 10 years. Mathers CPR 2022. This is important because these extra colonic cancers are difficult to detect and manage. The same trial found that aspirin significantly reduced the risk of colorectal cancer.
