Does reheating food lower the glycemic index? An in-depth look at resistant starch

October 16, 2025 •

3 min read

Research has shown that consuming reheated, starchy foods, such as pasta and rice, can lead to a significantly smaller blood glucose response compared to freshly cooked versions. This counter-intuitive process reveals how reheating food can lower its glycemic index (GI) by increasing the food's resistant starch content.

Quick Summary

The cook-cool-reheat process changes the molecular structure of starches in foods like rice, pasta, and potatoes through retrogradation. This creates resistant starch, a form of fiber that slows digestion and blunts the blood sugar response, effectively lowering the food's glycemic impact.

Key Points

Retrogradation is Key: Cooling starchy foods after cooking causes starches to realign into resistant starch.
Reheating Preserves the Benefit: Reheating doesn't typically destroy the resistant starch, preserving the GI benefit.
Blunts Blood Sugar Spikes: Resistant starch slows digestion, leading to a more controlled blood sugar response.
Works Best for Some Foods: Rice, pasta, and potatoes show significant GI changes with this method.
Boosts Gut Health: Resistant starch acts as a prebiotic, supporting gut bacteria.
Enhances Satiety: Slower digestion from resistant starch can increase feelings of fullness.
Requires Food Safety: Properly cool, refrigerate, and reheat foods to prevent illness.

What is the glycemic index?

The glycemic index (GI) ranks carbohydrate foods by how quickly they raise blood sugar. High-GI foods cause rapid blood sugar spikes, while low-GI foods lead to a slower, more gradual increase. Managing blood sugar is important for conditions like diabetes and overall metabolic health. A food's GI is influenced by factors such as fiber, fat, preparation method, and its chemical structure, particularly the starch structure and its accessibility to digestive enzymes.

The science behind reheating: Starch retrogradation

The effect of reheating on the GI of certain foods is due to starch retrogradation. Cooking starchy foods causes gelatinization, where starch granules swell and become easily digestible, increasing the GI. However, cooling these foods allows some starch molecules, especially amylose, to reform into a compact, ordered structure called resistant starch (RS3). This resistant starch is not digested in the small intestine but ferments in the large intestine, acting like fiber and feeding gut bacteria. Reheating doesn't completely reverse this retrogradation, allowing the food to retain a lower GI compared to its freshly cooked state.

Which foods are most affected?

The cook-cool-reheat method is most effective for starchy foods high in amylose, which readily recrystallizes when cooled. This includes:

Rice: Cooked white rice cooled for 24 hours at 4°C and then reheated shows a significantly higher resistant starch content and a lower glycemic response.
Pasta: Reheating previously chilled pasta can significantly lower the postprandial glucose response compared to freshly cooked pasta.
Potatoes: While the GI of potatoes varies, cooling can reduce it. The effect of reheating depends on the potato variety. Using waxy potatoes may yield better results.
Other Legumes and Grains: Lentils, beans, oats, and barley also produce resistant starch upon cooling and can be reheated.

How reheating impacts glycemic index: A comparison


Feature	Freshly Cooked Starchy Food (Hot)	Cooked, Cooled, and Reheated Starchy Food
Starch Structure	Gelatinized; starch molecules are swollen and accessible.	Retrograded; some starch molecules are recrystallized into a more compact, indigestible form.
Glycemic Index (GI)	Typically higher due to easy enzyme access and rapid digestion.	Typically lower because the resistant starch slows down carbohydrate digestion.
Blood Sugar Impact	Causes a faster, sharper increase in blood glucose levels.	Leads to a slower, more moderate rise in blood glucose levels.
Carb Absorption	Rapidly absorbed in the small intestine.	Partially resists digestion; some starch passes to the large intestine.

Health benefits of resistant starch beyond GI

Resistant starch, formed during the cook-cool-reheat process, offers health benefits beyond glycemic control. It acts as a prebiotic, feeding beneficial gut bacteria and producing short-chain fatty acids like butyrate, which supports gut health. Resistant starch can also increase feelings of fullness and potentially aid in weight management. Some studies also suggest it may improve insulin sensitivity.

Food safety considerations

When using the cook-cool-reheat method, especially with foods like rice that can harbor Bacillus cereus, proper food safety is crucial.

Cool cooked food rapidly: Refrigerate within two hours in shallow containers.
Store in the refrigerator: Store at or below 40°F (4°C) for at least 12-24 hours for maximum resistant starch formation.
Reheat thoroughly: Ensure food reaches an internal temperature of 165°F (74°C).
Discard after 3-4 days: Do not consume leftovers after this period.

Conclusion

Cooling and reheating starchy foods is a practical way to lower their glycemic index by increasing resistant starch content. This process can help manage blood sugar levels and offers additional benefits for gut health and satiety. This strategy can be a valuable addition to dietary approaches, especially for those managing blood sugar, such as individuals with diabetes {Link: Clemson HGIC website https://hgic.clemson.edu/factsheet/starch-retrogradation-a-method-for-post-mealtime-blood-sugar-management-in-individuals-with-diabetes/}. Always follow proper food safety guidelines when preparing and storing reheated foods.

Frequently Asked Questions

When starchy food is cooked and then cooled, a process called retrogradation occurs. This causes some starch molecules to recrystallize into a more compact structure known as resistant starch, which is more difficult for digestive enzymes to break down, resulting in a slower release of glucose and a lower GI.

Yes, reheating cooked white rice after it has been refrigerated for at least 24 hours has been shown to increase its resistant starch content significantly (up to 2.5 times more), which leads to a lower glycemic response than freshly cooked rice.

Research indicates that eating reheated pasta, after it has been chilled, can result in a smaller blood sugar spike than eating it freshly cooked. The process increases the resistant starch, which slows digestion.

For optimal results, cook your starchy food and then cool it completely in the refrigerator for at least 12-24 hours. When you are ready to eat, reheat the food thoroughly. This process maximizes the formation of resistant starch.

Yes, different potato varieties react differently. Waxy potatoes tend to have a lower GI, and cooling can further reduce it. Reheating may not have as pronounced an effect on GI in some varieties compared to others, but the chilling process itself is beneficial.

Reheating leftovers to a safe temperature (165°F or 74°C) does not typically destroy the resistant starch formed during cooling, as the recrystallized starch is more heat-stable than its original form.

Improper cooling can lead to the growth of bacteria like Bacillus cereus, which can cause food poisoning, often associated with rice. Always cool leftovers quickly in shallow containers and refrigerate promptly. Reheat thoroughly to a safe temperature before eating.