Does cornstarch spike your blood sugar? A deep dive into its glycemic impact

October 10, 2025 •

3 min read

With a reported glycemic index (GI) as high as 85, cooked cornstarch can cause a rapid increase in blood sugar, similar to table sugar. But does cornstarch spike your blood sugar in the small quantities typically used for cooking? The answer is nuanced, depending on preparation, quantity, and individual health factors.

Quick Summary

Cornstarch is a processed carbohydrate with a high glycemic index that can cause blood sugar spikes when cooked and consumed in large quantities. Its effect is reduced when used sparingly in a balanced meal.

Key Points

High Glycemic Index: Cooked cornstarch has a very high glycemic index, meaning it causes a rapid and significant rise in blood sugar.
Refined Carbohydrate: The manufacturing process removes all fiber and nutrients, leaving a pure carbohydrate that is quickly absorbed and converted to glucose.
Moderation is Key: In small amounts used for thickening (e.g., a tablespoon in a dish), cornstarch's impact on blood sugar is minimal for most people.
Concern for Diabetics: Individuals with diabetes or insulin resistance should be more mindful of cornstarch intake, especially in larger quantities, as it can disrupt blood sugar management.
Uncooked vs. Cooked: The cooking process increases cornstarch's digestibility and glycemic impact. Uncooked cornstarch is slower to digest and is sometimes used therapeutically for specific medical conditions.
Healthier Alternatives: Substituting cornstarch with alternatives like arrowroot powder, almond flour, or ground flaxseed adds beneficial fiber and nutrients to your diet while effectively thickening foods.

What Exactly is Cornstarch?

Cornstarch is a fine, powdery substance derived from the endosperm of the corn kernel through a wet milling process. This manufacturing process strips the corn of its fibrous outer bran and germ, leaving behind a pure, refined carbohydrate. This refinement is key to understanding its nutritional impact. Because it lacks fiber, protein, and fat, cornstarch offers virtually no nutritional value beyond its caloric content. It is primarily used as a thickening agent in sauces, soups, and desserts, and can provide a crisp texture to fried foods.

The Glycemic Index of Cornstarch

The glycemic index (GI) is a system that ranks carbohydrates on a scale from 0 to 100 based on how they affect blood sugar levels after consumption. Foods with a high GI are quickly digested and absorbed, causing a rapid and sharp spike in blood glucose.

Cooked cornstarch has a very high GI, with some sources listing its value at 85 or even higher. This high GI is due to its composition as a pure, simple carbohydrate that is rapidly broken down by the body into glucose. For individuals with diabetes or those monitoring their blood sugar, this rapid spike can be problematic.

The crucial difference between cooked and uncooked cornstarch

Interestingly, the cooking process significantly alters cornstarch's glycemic impact. When heated, cornstarch's molecules change, becoming more easily digestible and causing a faster blood sugar response. Conversely, uncooked cornstarch is digested much more slowly, with some studies showing its use as a supplement to prevent nocturnal hypoglycemia in people with certain conditions. However, uncooked cornstarch is not recommended for general consumption due to digestibility issues and should only be used under medical supervision.

Factors Affecting Cornstarch's Impact

The overall effect of cornstarch on your blood sugar is not determined by its GI alone. Several other factors play a role, including:

Quantity: Most recipes only call for a small amount of cornstarch (1-2 tablespoons) distributed among several servings. In these small quantities, the blood sugar impact is minimal, especially when combined with other ingredients.
Meal Composition: When consumed as part of a meal that includes fiber, protein, and fat, the absorption of glucose is slowed down. For example, a sauce thickened with cornstarch that is served with a protein like chicken and a fibrous vegetable will have a less dramatic effect than a sugary dessert thickened with cornstarch.
Individual Health: For individuals with diabetes or insulin resistance, even small amounts can be a concern. Monitoring blood glucose is essential to understand personal tolerance.

Healthier Alternatives to Cornstarch

For those looking to reduce their reliance on refined carbohydrates like cornstarch, several nutritious and effective alternatives exist. These options often provide additional nutritional benefits like fiber and protein, which help regulate blood sugar more effectively.

Arrowroot Powder: A gluten-free thickener similar to cornstarch but with a lower glycemic impact.
Almond Flour: Contains healthy fats and fiber, making it a low-carb alternative for baking and thickening.
Ground Flaxseeds: Forms a gel-like consistency when mixed with water and is rich in fiber and omega-3 fatty acids.
Psyllium Husk: An excellent source of soluble fiber that can be used to thicken liquids.
Oat Flour: A gluten-free option with more fiber and protein than cornstarch.

Comparison Table: Cornstarch vs. Healthier Alternatives


Feature	Cornstarch	Arrowroot Powder	Almond Flour	Ground Flaxseed
Glycemic Index	High (85+)	Lower	Low	Low
Nutrient Density	Minimal (Carbs only)	More fiber and minerals	Fiber, protein, healthy fats	Fiber, omega-3s
Best Uses	Clear sauces, pie fillings	Clear sauces, fruit pies	Baking, low-carb thickening	Baking, thickening, egg substitute
Cooking Note	Creates a cloudy finish	Best added at the end of cooking	Requires more liquid	Can impart a nutty flavor

Conclusion

While cornstarch is a versatile and common kitchen ingredient, its impact on blood sugar levels should not be ignored, especially for those managing diabetes or concerned about refined carbohydrate intake. Due to its highly processed nature and high glycemic index when cooked, cornstarch can cause significant blood sugar spikes, particularly in large quantities. However, when used in moderation as a small part of a balanced, nutrient-rich meal, its effects are likely minimal for most people. For those seeking better blood sugar control, exploring alternative thickeners like arrowroot powder, almond flour, or ground flaxseeds offers a way to maintain flavor and texture while improving the nutritional profile of your meals. As with any dietary concern, consulting a healthcare professional is recommended for personalized advice on managing your blood sugar. For more information on carbohydrates and diabetes, you can visit the American Diabetes Association website.

Frequently Asked Questions

Cooked cornstarch has a high glycemic index because it is a highly refined carbohydrate with no fiber. When heated, its molecules are easily broken down and absorbed by the body, causing a rapid spike in blood glucose.

For most people, the small amount of cornstarch (1-2 tablespoons) used for thickening an entire dish will have a minimal impact on blood sugar. The effects are more pronounced when consuming larger quantities.

Healthier and nutrient-rich alternatives include arrowroot powder, almond flour, oat flour, and ground flaxseed. These options often provide more fiber, which helps slow sugar absorption.

Yes, uncooked cornstarch is digested much more slowly than cooked cornstarch and can be used medically to prevent nocturnal hypoglycemia in certain conditions. However, it should only be consumed under a doctor's supervision.

Individuals with type 2 diabetes, insulin resistance, or anyone actively managing their blood sugar levels should limit their cornstarch intake. Others concerned with overall nutrient density may also opt for alternatives.

Since cornstarch is a calorie-dense, refined carbohydrate, regular consumption in large quantities can contribute to weight gain. Foods with cornstarch are often also processed and contain added sugars and fats.

Consuming cornstarch as part of a meal containing fiber, protein, and fat can help slow the absorption of glucose. This mitigates the rapid blood sugar spike that would occur if consumed alone.