Does Refrigerating Rice Lower Glycemic Index? The Science Behind It

October 29, 2025 •

3 min read

According to a 2015 study published in the Asia Pacific Journal of Clinical Nutrition, cooked white rice that is refrigerated for 24 hours can significantly lower its glycemic response. This happens through a process called retrogradation, which increases resistant starch and confirms that refrigerating rice does lower glycemic index.

Quick Summary

Cooling and reheating cooked rice increases its resistant starch content, which functions similarly to fiber. This process slows down digestion, resulting in a lower glycemic response and improved blood sugar control.

Key Points

Resistant Starch Formation: Cooking and subsequent cooling of rice creates resistant starch (RS3), a type of fiber that resists digestion in the small intestine.
Lower Glycemic Index: The formation of resistant starch slows the release of glucose into the bloodstream, leading to a significantly lower glycemic response.
Reheating Doesn't Reverse It: The beneficial effects of retrograded starch remain largely intact even after the rice is reheated, as the new structure is heat-resistant.
Health Benefits: The resistant starch acts as a prebiotic, feeding healthy gut bacteria and potentially aiding in weight management and improved cholesterol.
Food Safety is Crucial: Rapidly cool cooked rice and refrigerate within one hour to prevent the growth of harmful bacteria like Bacillus cereus.
Ideal Rice Types: Higher-amylose rice varieties, such as basmati or long-grain, produce more resistant starch than short-grain varieties when cooled.

The Science Behind Cooling Rice

When you cook rice, the heat and moisture cause the starch molecules to swell and become gelatinized, making them easily digestible. This is why fresh, hot rice can cause a rapid spike in blood sugar. However, the science changes entirely once the rice is cooled.

What is Starch Retrogradation?

Starch retrogradation is a process that occurs when gelatinized starch cools. As the rice cools, the starch molecules re-associate and form a more compact, crystalline structure that is more resistant to digestion by the enzymes in your small intestine. This newly formed, indigestible starch is known as resistant starch (RS3), and it behaves much like dietary fiber.

Reheating Does Not Reverse the Effect

A common misconception is that reheating the cooled rice will reverse the process and raise its glycemic index back to its original level. Research shows this is not the case. The crystalline structure of the retrograded starch is heat-resistant, so even when reheated, the rice retains a significantly higher amount of resistant starch than it had when freshly cooked.

Maximizing Resistant Starch and its Health Benefits

The Cooking and Cooling Process

To get the most benefit, it is recommended to refrigerate cooked rice for a minimum of 12-24 hours.

Cook the rice as you normally would.
Cool it quickly after cooking to a safe temperature. Spreading it in a thin layer can help accelerate this process.
Refrigerate the rice in a sealed container for at least 12 hours.
Reheat when ready to eat, or consume cold.

The Health Benefits

The increased resistant starch in cooled rice offers several health advantages:

Improved blood sugar control: By slowing down the absorption of glucose into the bloodstream, resistant starch prevents the rapid blood sugar spikes associated with high-glycemic foods.
Enhanced gut health: Resistant starch acts as a prebiotic, feeding the beneficial bacteria in your large intestine. This fermentation process produces short-chain fatty acids, like butyrate, which nourish the colon and support overall digestive wellness.
Weight management: The slower digestion and fermentation of resistant starch can lead to a greater feeling of fullness, potentially helping to reduce overall calorie intake. Additionally, studies suggest resistant starch may lead to slightly fewer calories being absorbed.
Lowered cholesterol: Some studies have indicated that resistant starch can help reduce blood cholesterol levels.

Comparing Freshly Cooked vs. Cooled and Reheated Rice


Feature	Freshly Cooked Rice	Cooled and Reheated Rice
Resistant Starch	Low	Significantly Higher
Glycemic Index (GI)	High	Lower
Digestion Speed	Rapid	Slowed
Blood Sugar Response	High spike	Lower, more gradual rise
Effect on Gut Health	Minimal	Acts as a prebiotic, feeds good gut bacteria

Important Safety and Usage Guidelines

Food Safety Is Paramount

It is critical to follow food safety protocols to prevent food poisoning, especially when handling rice. The bacteria Bacillus cereus can grow on cooked rice left at room temperature. To prevent this, cool cooked rice rapidly within one hour and refrigerate it promptly. Ensure reheated rice is steaming hot throughout before consuming.

Choosing the Right Rice

While this process works on all starchy foods like rice, pasta, and potatoes, certain types of rice may show a more pronounced effect. High-amylose rice varieties, such as basmati or long-grain rice, tend to form more resistant starch during cooling compared to short-grain varieties.

Conclusion

By simply refrigerating cooked rice for a day, you can increase its content of resistant starch and effectively lower its glycemic index. This simple food preparation hack provides tangible health benefits, including better blood sugar control, improved gut health, and potential support for weight management. While it's particularly valuable for those managing blood sugar, it's a worthwhile dietary modification for anyone looking to improve their health. For further reading on the science of resistant starch, consult this review from the National Institutes of Health.

Frequently Asked Questions

For optimal resistant starch formation, refrigerate cooked rice at 4°C (39°F) for at least 12-24 hours.

Yes, you can. Reheating cooled rice does not destroy the resistant starch. Studies show that reheated rice retains a lower glycemic response than freshly cooked rice.

This process works with most starchy foods, including all rice varieties. However, long-grain or basmati rice varieties, which are higher in amylose, tend to produce more resistant starch when cooled.

The main benefit is a lower glycemic response, meaning it causes a smaller, slower rise in blood sugar compared to fresh rice. This is especially helpful for individuals managing diabetes.

Yes. Improperly stored rice can harbor the Bacillus cereus bacteria, which can cause food poisoning. Always cool the rice rapidly within one hour of cooking and refrigerate it properly.

Resistant starch passes undigested into the large intestine, where it is fermented by beneficial gut bacteria. It acts as a prebiotic, feeding these bacteria and supporting a healthy microbiome.

Since resistant starch is not fully digested, some sources suggest that cooled rice may have slightly fewer absorbable calories than fresh rice. Estimates vary, but studies have indicated a modest reduction.