The Cooling Effect: Does Refrigerating Cooked Rice Lower the Glycemic Index?

October 5, 2025 •

4 min read

According to a 2015 study, cooked rice that was refrigerated for 24 hours and then reheated showed a significantly lower glycemic response in healthy adults compared to freshly cooked rice. This surprising effect is due to a change in the rice's starch composition, raising the question: Does refrigerating cooked rice lower the glycemic index?

Quick Summary

Refrigerating cooked rice overnight triggers a process called retrogradation, converting digestible starches into resistant starches. This change slows down digestion and glucose absorption, resulting in a lower glycemic index and a more stable blood sugar level when consumed.

Key Points

Resistant Starch Formation: Cooling cooked rice causes starch molecules to re-crystallize, forming resistant starch (Type 3) that is less easily digested.
Lower Glycemic Response: The increase in resistant starch leads to a lower glycemic index, meaning a smaller and slower blood sugar spike after consumption.
Optimal Cooling Time: For maximum benefit, refrigerate cooked rice for at least 12-24 hours.
Reheating Maintains Benefit: Reheating the rice does not undo the resistant starch formation, so you can enjoy it warm without losing the lowered GI effect.
Important Food Safety: Always refrigerate cooked rice within one hour of cooking and reheat until steaming hot to prevent bacterial growth.

The Science Behind Starch: Cooking, Cooling, and Glycemic Response

For billions of people worldwide, rice is a dietary staple, but its high glycemic index (GI) can be a concern for those managing blood sugar levels, such as individuals with diabetes. The glycemic index measures how quickly a food containing carbohydrates raises blood glucose. Foods with a high GI, like freshly cooked white rice, cause a rapid spike in blood sugar, while low-GI foods result in a slower, more gradual rise. The difference lies in the starch.

Starch is a complex carbohydrate made of long chains of glucose molecules. When rice is cooked, the heat and water cause the starch to gelatinize, making it easily digestible. Our digestive enzymes rapidly break down this gelatinized starch into glucose, which is then absorbed into the bloodstream. This leads to the characteristic blood sugar spike associated with many starchy foods.

The Magic of Retrogradation and Resistant Starch

When cooked rice is cooled, particularly under refrigeration for an extended period (12-24 hours), a process called starch retrogradation occurs. During retrogradation, the starch molecules re-align and re-crystallize, forming a type of starch known as resistant starch (specifically, Type 3 or RS3). This retrograded starch is less accessible to digestive enzymes, hence the name 'resistant starch'. It functions more like dietary fiber, passing through the small intestine largely undigested and eventually fermenting in the large intestine.

This resistance to digestion is the key to lowering the glycemic response. Because less of the starch is broken down and absorbed as glucose in the small intestine, the overall glucose load on the body is reduced, leading to a smaller and more controlled blood sugar increase.

Scientific Evidence: From Lab to Plate

Multiple studies have investigated this phenomenon, with a consistent finding: chilling cooked rice increases its resistant starch content and lowers its GI. A 2015 randomized controlled trial found that cooked white rice, cooled for 24 hours at 4°C and then reheated, produced a significantly lower glycemic response than freshly cooked rice. Another study noted that this process could lower the GI of white rice from around 78 to 54, a substantial reduction. The positive effect on blood glucose has also been observed in people with type 1 diabetes, though it's important to be mindful of insulin dosage.

It's worth noting that the effect size can vary depending on the type of rice and the preparation method. For instance, rice varieties with a higher amylose content (a component of starch) naturally have a lower GI, and cooling further enhances this effect. The cooking method also plays a role; one study found that the cooling effect was most pronounced in rice boiled by absorption, where water is fully absorbed by the rice, rather than methods involving excess water.

Optimizing Your Rice for a Lower Glycemic Impact

To make the most of this dietary hack, follow these steps:

Cook Your Rice as Usual: Prepare your rice using your preferred method. Using a method with high amylose content, like Basmati, may provide a better starting point for a lower GI.
Cool it Promptly: As soon as the rice is cooked, transfer it to a shallow dish to help it cool faster. For food safety, it is crucial to refrigerate the rice within one hour of cooking.
Refrigerate for Best Results: Place the rice in the refrigerator at 4°C for at least 12 to 24 hours. This is the optimal time for the retrogradation process to occur.
Reheat and Enjoy: You can reheat the rice in a microwave or on the stovetop. Reheating does not destroy the resistant starch that has formed. Be sure to heat it thoroughly until steaming hot to eliminate any potential bacteria, like Bacillus cereus, which can grow on rice left at room temperature for too long.

Comparison: Freshly Cooked vs. Refrigerated and Reheated Rice


Feature	Freshly Cooked Rice	Refrigerated & Reheated Rice
Resistant Starch	Low	Higher due to retrogradation
Glycemic Index (GI)	High	Lower
Blood Sugar Impact	Faster, more pronounced spike	Slower, more controlled rise
Digestion Speed	Rapid	Slower
Gut Health	Minimal impact	Acts as a prebiotic, feeding beneficial gut bacteria
Texture	Soft and fluffy	Slightly firmer and drier

Conclusion

For those looking to moderate their blood sugar response to rice, the answer is a resounding yes: refrigerating cooked rice does lower the glycemic index. The simple act of chilling rice for 12-24 hours converts a portion of its starches into resistant starch, which behaves more like a dietary fiber, slowing down digestion and providing a more gradual release of glucose. This straightforward food preparation technique offers a measurable nutritional benefit, particularly for individuals focusing on glycemic control. While it is not a complete solution for managing diabetes, it is a valuable and easy-to-implement strategy for making a staple food healthier. For the safest practice, always refrigerate promptly after cooking and reheat thoroughly before eating.

More on Resistant Starch

For an in-depth scientific review on resistant starch and its health benefits, including improving insulin sensitivity and gut health, you can explore detailed findings on the National Institutes of Health (NIH) website.

Frequently Asked Questions

Refrigerating cooked rice causes some of its digestible starches to convert into resistant starch through a process called retrogradation. This resistant starch is not easily broken down by the body's digestive enzymes, which slows down the absorption of glucose and lowers the food's glycemic index.

Yes, you can safely reheat the cooled rice. The resistant starch formed during the refrigeration process is stable and will not revert to its original, easily digestible form when reheated. Ensure you reheat the rice thoroughly until steaming hot.

Both refrigeration and freezing increase resistant starch. Freezing can even be a more effective method for some starches. A study on instant rice found a lower GI in rice that was frozen before drying compared to rice that was just chilled. For home cooking, both methods work, but a 24-hour chilling period is a common and effective approach.

Cooking rice by absorption and then chilling it is an effective method. Some research also suggests adding a small amount of fat, like coconut oil, during cooking before cooling can further enhance the resistant starch content.

The principle of starch retrogradation applies to other starchy foods as well. Cooling and reheating potatoes and pasta, for example, have also been shown to increase resistant starch and lower their glycemic index.

Clinical studies have shown that refrigerated and reheated rice can lead to a significantly smaller blood glucose response compared to fresh rice. The exact effect can vary based on the individual and the rice type, but the difference is notable and can assist with glycemic control.

Yes. It's critical to cool and refrigerate the rice promptly, ideally within one hour of cooking, and to reheat it to a steaming temperature. This prevents the growth of Bacillus cereus, a bacteria that can cause food poisoning if rice is left at room temperature for too long.