Does Boiling Potatoes Reduce the Glycemic Index?

October 16, 2025 •

4 min read

According to scientific studies, the way a potato is cooked significantly alters its impact on blood sugar. This article explores a common question: does boiling potatoes reduce the glycemic index and what cooking methods truly help?

Quick Summary

Boiling potatoes initially increases their glycemic index, but a specific cooling process changes their starch structure, significantly lowering the glycemic impact. This effect is crucial for blood sugar management.

Key Points

Boiling Alone Increases GI: When consumed hot, freshly boiled potatoes have a high glycemic index because boiling gelatinizes the starch, making it easily digestible.
Cooling is the Key: Refrigerating boiled potatoes for at least 12 hours promotes the formation of resistant starch, which significantly lowers the glycemic index.
Resistant Starch is Beneficial: This indigestible starch acts like a fiber, slowing glucose absorption and benefiting gut health.
Reheating Maintains Lower GI: Studies show that reheating chilled potatoes does not eliminate the lower glycemic impact achieved through the cooling process.
Potato Type Matters: Waxy varieties (like red potatoes) and new potatoes typically have a lower GI than starchy russets.
Combining with Fat/Protein Helps: Eating potatoes with fat, protein, or acid (like vinegar) can further reduce the overall glycemic load of a meal.

The Surprising Truth About Boiling Potatoes

When you boil a potato, the heat and water cause the starch granules to swell and gelatinize. This process, called gelatinization, makes the starch more accessible to the body's digestive enzymes. The result is that a freshly boiled, hot potato has a relatively high glycemic index (GI), as its carbohydrates are quickly broken down into glucose and absorbed into the bloodstream, causing a rapid spike in blood sugar. A hot, boiled white potato has an average GI of 82. This is in stark contrast to the widespread belief that boiling alone is a surefire way to lower a food's GI. Therefore, the simple act of boiling does not inherently reduce the glycemic impact when consumed hot.

The Magic of Cooling: How Resistant Starch is Formed

For those looking to lower the GI of their potatoes, the secret isn't in the boiling itself but in what happens afterward. The key lies in a process called retrogradation, which occurs when a cooked potato is cooled.

Boil the potatoes: Cook your potatoes as you normally would, until tender.
Cool completely: Transfer the potatoes to the refrigerator and let them cool for at least 12-24 hours.
Resistant starch formation: During this cooling period, some of the digestible starch retrogrades, or rearranges into a crystalline structure. This new structure is known as resistant starch (RS).
Benefits of resistant starch: Resistant starch is not broken down in the small intestine but instead ferments in the large intestine, where it acts like a soluble fiber. This process has several benefits, including a much smaller impact on blood glucose levels and providing fuel for beneficial gut bacteria.

Research has shown this effect can be significant. Studies have demonstrated that a boiled and then chilled potato can reduce its GI by 25–40%. In one specific example, a red potato served hot had a GI of 89, which dropped to 56 when served cold. Interestingly, further studies indicate that reheating the chilled potato for consumption does not negate this effect, and can even offer additional benefits.

Factors That Influence a Potato's Glycemic Index

Beyond just cooling, several other factors contribute to a potato's overall GI and how it affects blood sugar. Understanding these can help you make more informed dietary choices.

Potato Variety: Different potato types have varying starch compositions. Waxy potatoes, such as red or fingerling varieties, typically have a lower GI than starchy varieties like Russets or Idaho potatoes. Sweet potatoes also generally have a lower GI than white potatoes.
Serving Temperature: As discussed, consuming potatoes cold or reheated after cooling dramatically lowers the GI due to resistant starch formation.
Added Ingredients: Pairing potatoes with healthy fats, fiber, or protein can slow down the overall digestion process and help manage blood sugar spikes. Examples include adding olive oil, pairing with a protein source, or incorporating into a fiber-rich salad.
Portion Size: Even with lower-GI methods, portion control is vital for managing blood sugar effectively, as the glycemic load (GL) is determined by both the GI and the amount of food consumed.

Practical Strategies for a Lower GI Potato

Here is a side-by-side comparison of different potato preparation methods and their glycemic impact, followed by specific tips for reducing the GI.


Preparation Method	GI Impact	Key Takeaway
Boiled (Hot)	High	Starch is gelatinized and easily digestible, leading to a quick blood sugar spike.
Boiled (Cooled)	Lower	Retrogradation increases resistant starch content, which is less digestible and provides a lower glycemic response.
Baked (Hot)	Highest	High, dry heat fully gelatinizes starch, making it highly digestible.
Mashed	Very High	Processing breaks down starch structure, increasing its availability for digestion.
French Fries	Medium to High	Frying can create a lipid-amylose complex that offers some resistance, but overall GI is high due to rapid digestion.
Boiled, Cooled, and Reheated	Lowest	Maximum resistant starch formation occurs during the cool-down and reheat cycle.

Conclusion

While boiling a potato in itself doesn't significantly lower its glycemic index when eaten hot, the crucial step of cooling the cooked potato causes a profound change. This process of retrogradation increases the amount of resistant starch, which dramatically reduces the glycemic impact. By understanding the roles of cooking method, temperature, potato variety, and food pairings, it is entirely possible to enjoy potatoes as part of a balanced diet while still managing blood sugar levels effectively. For the lowest possible GI, boil your potatoes, cool them completely in the refrigerator, and then enjoy them cold or lightly reheated. For an extra benefit, be sure to eat the skin and pair them with sources of healthy fat and protein. For further reading on the science of resistant starch, you can explore academic resources such as this article from Wiley Online Library on the impact of starch storage conditions(https://onlinelibrary.wiley.com/doi/full/10.1002/star.201900281).

Frequently Asked Questions

The GI of potatoes is significantly affected by cooking methods and temperature. Cooking, especially with high heat, makes starch more digestible, increasing GI. However, cooling cooked potatoes dramatically lowers their GI due to resistant starch formation.

Resistant starch is a type of carbohydrate that resists digestion and acts like a dietary fiber. It is created through retrogradation, a process where cooked, gelatinized starches recrystallize upon cooling.

Yes, you can. Reheating cooked and cooled potatoes does not eliminate the resistant starch that has formed. Studies indicate that the lower glycemic impact is maintained even after reheating.

In general, waxy potato varieties, such as red or fingerling potatoes, have a lower GI than their starchy counterparts like Russets. Some varieties like Carisma are bred to be low-GI.

For the lowest GI, boil potatoes and then cool them in the refrigerator for at least 12 hours before eating. Serving them cold (e.g., in potato salad) or reheating them lightly after cooling are both effective methods.

Leaving the skin on a potato adds more fiber to your meal. This fiber helps to slow down the digestive process, which can lead to a more gradual increase in blood sugar and a lower overall glycemic impact.

Pair your potatoes with ingredients that also help control blood sugar. Adding healthy fats (olive oil, butter), protein, fiber, or acidic ingredients (vinegar, citrus juice) will slow digestion and reduce the overall glycemic impact of the meal.