Retrograded Starch (Resistant Starch Type 3)
The cooking trick that turns rice into a prebiotic — cooling cooked starch restructures it into a form that feeds gut bacteria instead of spiking blood sugar.
— Definition
Resistant Starch Type 3 (RS3) is retrograded starch — formed when gelatinised starch (cooked) is cooled, causing the amylose chains to recrystallise into a form that resists digestive enzymes in the small intestine.
— In Detail
The retrogradation process: when starch is cooked (gelatinised), the crystalline structure breaks down and the starch becomes fully digestible. Upon cooling, amylose chains reassociate and form new crystalline structures — RS3. This structural change is only partially reversed by reheating: once RS3 forms, roughly 40–50% remains as resistant starch even after reheating. Quantitative increases: freshly cooked white rice has ~0.6g RS per 100g. Cooked and refrigerated (4°C, 24 hours) white rice has ~1.65g RS. Heirloom rice varieties with higher amylose content (like Chak-Hao) start with more RS and produce more RS3 on cooling. Practical implication: eating rice cooked the previous day provides approximately 2–3× more resistant starch than freshly cooked rice. The traditional Indian and Japanese practices of eating cold or room-temperature leftover rice inadvertently optimised RS3 intake.
— Why It Matters
RS3 functions as a prebiotic — it reaches the colon intact and feeds Bifidobacterium and Lactobacillus, which produce butyrate (the primary fuel for colonocytes). The GI of cooked-and-cooled rice is also significantly lower than freshly cooked rice, making it the simplest possible dietary intervention for both gut health and blood sugar management.
— Related Terms
— See in Field Guide
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