Why does rice when placed in the fridge become resistant rice?

October 31, 2025 •

3 min read

According to a 2015 study, cooked rice that was cooled for 24 hours and then reheated had more than double the resistant starch compared to freshly cooked rice. This phenomenon explains why does rice when placed in the fridge become resistant rice, turning a simple leftover into a functional food with added health benefits.

Quick Summary

This article explains the scientific process of starch retrogradation, which causes cooked rice to form resistant starch when cooled. Learn how this transformation impacts digestion, blood sugar, and gut health.

Key Points

Starch Retrogradation: The cooling of cooked rice causes starch molecules to re-crystallize, forming resistant starch.
Prebiotic Fiber: Resistant starch acts as a prebiotic, feeding beneficial bacteria in your large intestine and improving gut health.
Lower Glycemic Response: Eating cooled rice leads to a lower and more gradual rise in blood sugar compared to freshly cooked rice.
Increased Satiety: Resistant starch can help you feel fuller for longer, which can assist with weight management.
Proper Food Safety: To avoid food poisoning, always cool and refrigerate leftover rice promptly, and reheat it thoroughly before eating.
Reheating Maintains Benefits: The resistant starch formed through cooling is heat-stable, so you can reheat the rice and still reap the health benefits.

What is Resistant Starch?

Resistant starch (RS) is a type of carbohydrate that is not fully digested in the small intestine. Instead, it travels to the large intestine where beneficial gut bacteria ferment it. This process is similar to how dietary fiber functions, offering health advantages like feeding the gut microbiome and potentially improving insulin sensitivity. Freshly cooked rice contains rapidly digestible starches, which are quickly broken down into glucose, causing a spike in blood sugar. By transforming into resistant starch, cooled rice alters its nutritional profile and how the body processes it.

The Science Behind Starch Retrogradation

During cooking, starch granules in rice gelatinize, swelling and absorbing water. The starch molecules, amylose and amylopectin, lose their structure. Cooling reverses this somewhat through retrogradation. In the refrigerator's low temperatures, amylose chains re-associate and re-crystallize into a denser structure. This structure is harder for digestive enzymes in the small intestine to break down, increasing resistant starch content. Research indicates that cooling cooked white rice at about 4°C (39°F) for 24 hours can significantly boost its resistant starch.

Health Benefits of Resistant Rice

Adding resistant starch to your diet by cooling rice can lead to various health improvements. These benefits arise because resistant starch behaves like fiber. A healthy gut microbiome is crucial for well-being, and resistant starch acts as a prebiotic to support it. Key health benefits include:

Improved Blood Sugar Control: Resistant starch isn't easily converted to glucose, leading to a slower and lower rise in blood sugar after consumption. This is beneficial for managing blood sugar, especially for individuals with diabetes.
Enhanced Gut Health: Acting as a prebiotic, resistant starch nourishes beneficial bacteria in the large intestine. These bacteria produce short-chain fatty acids like butyrate, which fuels colon cells and reduces inflammation.
Increased Satiety: Resistant starch can promote feelings of fullness for longer periods, potentially aiding weight management by reducing overall calorie intake.

How to Maximize Resistant Starch in Rice

To optimize resistant starch, follow these simple steps when preparing and storing rice. This method works for other starchy foods too, like pasta and potatoes, but is particularly effective for rice.

Cook normally: Prepare your rice as usual.
Cool rapidly: Spread the cooked rice to cool quickly at room temperature.
Refrigerate: Store the cooled rice in a covered container in the refrigerator for 12 to 24 hours. This maximizes resistant starch formation.
Eat or Reheat: The rice can be eaten cold or reheated. Reheating doesn't significantly reduce the resistant starch formed during cooling.

Comparison: Freshly Cooked vs. Cooled & Reheated Rice


Feature	Freshly Cooked Rice	Cooled & Reheated Rice
Starch Composition	Mostly rapidly digestible starch.	Higher proportion of resistant starch.
Digestibility	Easily digested in the small intestine.	Resists digestion in the small intestine.
Glycemic Response	Higher blood sugar spike.	Lower blood sugar response.
Gut Health Impact	Minimal prebiotic effect.	Acts as a prebiotic, feeding beneficial gut bacteria.
Calorie Absorption	More calories absorbed by the body.	Fewer calories absorbed due to undigested starch.
Texture	Soft and fluffy.	Tends to be firmer or chewier.

Safety Considerations for Leftover Rice

While beneficial, proper food safety with leftover rice is vital. Bacillus cereus, a bacterium producing toxins causing food poisoning, can grow in cooked rice left at room temperature. To minimize risk:

Refrigerate cooked rice within two hours of cooking.
Store rice in an airtight container in the fridge.
Consume leftovers within a few days and reheat thoroughly.

Conclusion

Chilling cooked rice transforms it into a functional food with higher resistant starch. Retrogradation alters starch molecules, leading to better blood sugar control, improved gut health, and increased fullness. This simple method makes rice a healthier dietary component. Always prioritize food safety when storing leftover rice to enjoy these benefits safely.

For more information on resistant starch, consult reputable sources such as the National Institutes of Health.

Frequently Asked Questions

The science behind this is a process called starch retrogradation. When cooked rice cools, the starch molecules re-form into a tighter, crystalline structure that is more resistant to digestion.

No, you do not. You can reheat the rice after it has been chilled, and the resistant starch will largely remain intact. Some of the benefits, like a lower glycemic response, will still apply.

The effect of retrogradation occurs in all starchy foods, including different types of rice. The most significant increase in resistant starch is typically observed in white rice.

For optimal resistant starch formation, refrigerating the cooked rice for at least 12 to 24 hours is recommended. Studies have shown that cooling for 24 hours at 4°C is effective.

Yes, as long as it is stored properly. Cooked rice should be refrigerated promptly (within two hours), and when reheating, it must be heated thoroughly to kill any bacteria like Bacillus cereus.

This same principle applies to other starchy foods. You can increase resistant starch in foods like pasta, potatoes, and even oats by cooking and then cooling them.

Because resistant starch is not easily broken down into glucose, it prevents the rapid absorption of sugar into the bloodstream. This results in a slower, more stable rise in blood sugar levels after a meal.