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Friday, March 28, 2025

Cooling Rice: A Simple Trick for Improved Insulin Sensitivity

Cooling cooked rice after cooking increases its resistant starch content through a process called starch retrogradation, which can help mitigate blood sugar spikes.

Here's a breakdown of the evidence:

Mechanism of Resistant Starch Formation

Cooling cooked rice (especially refrigeration) causes starch molecules to reorganize into a crystalline structure that resists digestion in the small intestine. This retrograded starch acts as resistant starch (RS), which:

  • Slows carbohydrate absorption, reducing rapid blood glucose spikes.
  • Ferments in the colon, producing short-chain fatty acids (SCFAs) that improve insulin sensitivity and glucose metabolism.

Impact on Blood Sugar Control

  1. Clinical Studies:
    • In type 1 diabetes patients, cooled rice (refrigerated for 24 hours) caused lower postprandial glucose peaks (9.9 vs. 11 mmol/L) and shorter time to peak compared to fresh rice.
    • A similar effect was observed in healthy individuals, with cooled rice lowering glycemic response by ~18%.
    • Meta-analyses confirm RS reduces fasting glucose and insulin resistance (HOMA-IR) in both diabetic and non-diabetic populations.
  2. Key Factors:
    • Dosage: Effects are stronger with ≥28 g/day of RS.
    • Storage Duration: Longer cooling (e.g., 24 hours at 4°C) increases RS content more than shorter periods.
    • Reheating: While reheating may slightly reduce RS content, cooled rice still retains benefits compared to fresh rice.

Practical Considerations

  • Hypoglycemia Risk: Cooled rice may increase hypoglycemic episodes in insulin-dependent individuals due to slower glucose release.
  • Other RS Sources: RS type II (e.g., from potatoes, legumes) and type III (retrograded starch) are more effective than RS type I (found in whole grains).

Because cooling rice enhances resistant starch formation, which can help stabilize blood sugar by slowing carbohydrate absorption. 

While the evidence is strongest for type II and retrograded starch, refrigerated rice remains a practical dietary strategy for managing glycemic responses.