Resistant starch (RS)

Resistant starch (RS) refers to the fraction of starch and starch-degradation products that escape digestion in the small intestine of healthy individuals and enter the colon to undergo bacterial fermentation. It is categorized into five types based on physical structure or chemical modification, including physically trapped starch (RS1), ungelatinized granules (RS2), and retrograded starch (RS3) (Birt et al., 2013, Adv Nutr). Once in the large intestine, it acts as a prebiotic substrate, selectively promoting the growth of beneficial bacteria and producing short-chain fatty acids like butyrate, which is essential for maintaining colon health and preventing neoplastic changes (Bird et al., 2010, World J Gastroenterol). Beyond its local effects in the gut, resistant starch significantly impacts systemic metabolism by slowing glucose absorption and enhancing insulin sensitivity, making it a focus for nutritional interventions in type 2 diabetes and obesity (Lockyer & Nugent, 2017, Nutr Bull). While it is not a traditional therapeutic target such as a protein receptor or enzyme, it functions as a critical dietary modulator of the gut-microbiome-axis. Clinically, it is used to manage glycemic index and promote satiety, though high intake may lead to transient gastrointestinal discomfort such as bloating or flatulence (Higgins, 2004, AOAC Int). Research also suggests a protective role in colorectal cancer due to its ability to lower fecal pH and reduce the concentration of secondary bile acids.

Other names

Non-digestible starchRetrograded starchRS1RS2RS3RS4RS5

Resistant starch resists enzymatic hydrolysis by alpha-amylase and glucoamylase in the small intestine, reaching the large intestine intact where it is fermented by anaerobic gut bacteria such as Ruminococcus bromii and Bifidobacterium species (Birt et al., 2013, Adv Nutr). This fermentation process produces short-chain fatty acids (SCFAs), primarily butyrate, acetate, and propionate, which lower luminal pH and serve as the preferred energy source for colonocytes (Topping & Clifton, 2001, Physiol Rev). SCFAs also act as signaling molecules by binding to G protein-coupled receptors (GPR41 and GPR43), which modulates the release of metabolic hormones like GLP-1 and PYY, thereby improving insulin sensitivity and promoting satiety (Lockyer & Nugent, 2017, Nutr Bull).