Does Refrigerating Mashed Potatoes Lower the Glycemic Index?

December 30, 2025 •

2 min read

Research has shown that cooling cooked potatoes can reduce their glycemic impact by as much as 40 percent. This is because refrigerating mashed potatoes triggers a natural process that changes the structure of its starches, lowering its glycemic index and making it a healthier option for blood sugar management.

Quick Summary

This guide explains the science of how cooling and reheating mashed potatoes increases resistant starch, which in turn lowers the glycemic index. Learn how this simple method can make a high-glycemic food a more blood sugar-friendly option.

Key Points

Retrogradation: When cooked potatoes are cooled, the starches undergo retrogradation, converting into a less digestible form known as resistant starch.
Lower Glycemic Index: The increase in resistant starch means the cooled mashed potatoes cause a slower, more gradual rise in blood sugar compared to when they are served hot.
Refrigerate overnight: For maximum resistant starch formation, refrigerate cooked mashed potatoes for at least 12–24 hours.
Reheating is fine: Reheating the cooled mashed potatoes does not destroy all the resistant starch, allowing you to still benefit from the lower glycemic index.
Additional strategies: Pairing with fats, fiber, or acidic ingredients like vinegar can further slow digestion and improve the blood sugar response.

The Science Behind Starch and Glycemic Index

Potatoes are primarily made up of carbohydrates, mainly starch. When cooked, these starches swell and become easily digestible, causing a rapid rise in blood sugar. This is why freshly cooked potatoes are considered a high-glycemic food.

The Magic of Retrogradation

Cooling cooked potatoes causes the gelatinized starches to recrystallize, forming a structure that is more resistant to digestion. This process is called retrogradation and it creates resistant starch (RS). Resistant starch acts like fiber, passing into the large intestine where it can support gut health.

Since resistant starch isn't broken down into glucose and absorbed into the bloodstream, it helps prevent the rapid blood sugar spikes typically associated with starchy foods. The longer the potatoes are refrigerated, the more resistant starch is formed.

How to Maximize the Effect

To increase resistant starch in mashed potatoes:

Cook and mash the potatoes.
Refrigerate for at least 12–24 hours. This allows sufficient time for resistant starch to develop.
Gentle reheating is fine, as resistant starch is largely retained.
Adding healthy fats can further slow digestion and moderate blood sugar.
Combining with fiber-rich foods can also help manage blood sugar levels.

Hot vs. Cooled Mashed Potatoes: A Comparison


Feature	Freshly Made (Hot)	Cooled (Refrigerated 12-24h)	Reheated (After Cooling)
Starch Type	Digestible starch	High resistant starch (RS)	Still retains significant RS
Glycemic Index	High	Low	Low (lower than freshly made)
Blood Sugar Impact	Rapid and high spike	Slower, more gradual rise	Slower, more gradual rise
Gut Health	Minimal prebiotic benefit	Excellent prebiotic benefit	Good prebiotic benefit
Best For	Immediate consumption	Meal prep and batch cooking	Enjoying a healthier version of a classic

Other Considerations for Lowering the GI

The type of potato matters; waxy varieties like red or fingerling potatoes typically have a lower GI than starchy russets. Adding an acidic ingredient, such as vinegar, can also help slow stomach emptying. Leaving the skins on adds beneficial fiber.

Conclusion: The Final Verdict

Refrigerating mashed potatoes does lower their glycemic index by increasing resistant starch through retrogradation. Cooking, cooling for at least 12 hours, and then serving them (even reheated) can make this high-GI dish more blood sugar-friendly. This technique is beneficial for blood sugar management, including for individuals with diabetes.

Can you still get the benefits if you reheat the potatoes?

Yes, reheating potatoes after cooling preserves most of the resistant starch. While eating them cold might offer the lowest GI, reheated cooled potatoes still have a lower glycemic impact than freshly made ones.

Frequently Asked Questions

Resistant starch is a type of carbohydrate that is not fully digested in the small intestine. It travels to the large intestine where it feeds beneficial gut bacteria, promoting gut health and helping to stabilize blood sugar levels.

For best results, you should refrigerate the mashed potatoes for at least 12 to 24 hours. This provides enough time for the retrogradation process to significantly increase the resistant starch content.

No, reheating does not destroy all of the resistant starch. While eating them cold may provide the lowest glycemic impact, reheating is still beneficial and results in a lower GI compared to freshly made potatoes.

Yes, this method of cooking, cooling, and reheating also works with other starchy foods like rice and pasta to increase their resistant starch content and lower their glycemic index.

Waxy potatoes, such as red or fingerling potatoes, tend to have a lower glycemic index than starchy russet varieties. Combining a waxy potato with the cooling method will maximize the GI-lowering effect.

Yes, as long as proper food safety protocols are followed. Be sure to refrigerate the potatoes promptly after cooking to prevent bacterial growth.

While the addition of milk and butter adds calories and fat, the cooling process will still effectively increase resistant starch and lower the glycemic index of the potato portion of the dish. A higher fat content in general can help slow digestion.