Is Cornstarch Ok on a Keto Diet? The Definitive Guide

December 13, 2025 •

4 min read

With approximately 7 grams of net carbs per tablespoon, cornstarch is unequivocally not considered a keto-friendly ingredient. For individuals on a very low-carb ketogenic diet, even a small amount of cornstarch can quickly use up the daily carbohydrate allowance and disrupt the metabolic state of ketosis.

Quick Summary

This guide explains why cornstarch is unsuitable for a ketogenic diet due to its high carbohydrate content and lack of nutritional value, and offers a comprehensive list of safe, low-carb alternatives for thickening sauces, gravies, and desserts.

Key Points

High in Carbs: Cornstarch contains about 7 grams of pure carbohydrates per tablespoon, making it incompatible with a low-carb ketogenic diet.
Disrupts Ketosis: The high glycemic load of cornstarch can cause a blood sugar spike and insulin release, knocking the body out of ketosis.
Lacks Nutritional Value: Cornstarch is a highly refined, processed food with minimal nutritional benefit, lacking essential fiber, vitamins, and minerals.
Multiple Alternatives Exist: Excellent keto-friendly thickeners include xanthan gum, guar gum, and glucomannan powder, which are low-carb and highly effective.
Choose the Right Substitute: The best replacement depends on your recipe, with options like xanthan gum being ideal for sauces and glucomannan for stews.
Careful Measurement is Key: Powerful thickeners like xanthan and guar gum require very small amounts and careful mixing to avoid over-thickening or clumping.

Why Cornstarch Is Not Keto-Friendly

Cornstarch, a highly refined powder derived from the starchy part of corn kernels, is a staple thickener in many kitchens. However, its macronutrient profile makes it entirely incompatible with the restrictive nature of a ketogenic diet. The core principle of keto is to severely limit carbohydrate intake, forcing the body to burn fat for fuel instead. A typical daily carb limit is between 20 and 50 grams, and cornstarch packs a significant amount of carbs into a very small serving. Just one tablespoon contains about 7 grams of carbohydrates, all of which are net carbs, with virtually no fiber to mitigate their effect on blood sugar.

When consumed, these simple carbohydrates are quickly converted into glucose, causing a rapid spike in blood sugar and a subsequent insulin release. This process is the exact opposite of what the keto diet aims to achieve. The insulin spike can prevent the body from entering or maintaining ketosis, stalling weight loss progress and potentially reversing the metabolic state. For those with a daily carb target of 20 grams, using just two tablespoons of cornstarch in a recipe would consume 70% of the day's allowance, leaving no room for other nutrient-dense vegetables or keto-friendly foods.

The Problem with High-Glycemic Refined Carbs

Beyond just the carb count, the quality of carbohydrates matters on keto. Cornstarch is an ultra-processed food that offers little to no nutritional value, lacking essential vitamins, minerals, and fiber. This contrasts with the goal of a well-formulated keto diet, which prioritizes nutrient-dense, whole foods. Regular consumption of high-glycemic foods like cornstarch has been linked to potential health risks, including blood sugar imbalances, insulin resistance, and an increased risk of heart disease. This makes it a poor choice for anyone focused on improving metabolic health.

How to Transition to Keto-Friendly Thickeners

Making the switch from cornstarch is straightforward once you know the right alternatives. The key is to find substitutes that provide thickening power without the heavy carb load. Experimenting with different options will help you discover which ones work best for various types of recipes. Start by making small batches to test the consistency and flavor, as the substitution ratio is often not one-to-one.

Keto-Friendly Cornstarch Alternatives

There are several excellent low-carb options to use instead of cornstarch for thickening sauces, gravies, and desserts. Each offers a different set of properties, making some more suitable for specific applications than others.

Xanthan Gum: Derived from fermented sugar, this powerful thickener is a favorite in the keto community. Only a very small amount is needed, often half a teaspoon or less, resulting in virtually zero net carbs per serving. It works well in hot and cold preparations, from sauces to ice cream. However, it's crucial to add it slowly and whisk vigorously to prevent clumping.
Guar Gum: Similar to xanthan gum, guar gum is a fiber-rich powder that acts as an effective thickener and binder. It has minimal net carbs and is a great substitute for cornstarch, though it can become slimy if too much is used.
Glucomannan Powder: Made from the konjac plant, glucomannan is a highly effective, viscous dietary fiber that has no net carbs. It is often used to make shirataki noodles and is an excellent thickener for soups and stews. Like xanthan gum, it requires careful measurement to avoid over-thickening.
Almond Flour: While not a traditional thickener, a small amount of finely ground almond flour can thicken sauces and batters by absorbing moisture. It imparts a nutty flavor and is best used in recipes where the taste is complementary.
Coconut Flour: This high-fiber, low-carb flour absorbs a lot of liquid, making it a decent thickener for some gravies and casseroles. It adds a distinct coconut flavor, so consider your recipe when using it.

Comparison Table: Cornstarch vs. Keto-Friendly Thickeners


Feature	Cornstarch	Xanthan Gum	Guar Gum	Glucomannan Powder
Net Carbs (per tbsp)	~7g	~0g	<1g	~0g
Thickening Power	Moderate	Very High	Very High	Very High
Best for Hot Use	Yes	Yes	Yes	Yes
Best for Cold Use	No	Yes	Yes	Yes
Requires Careful Measurement?	Standard	Yes, prone to clumping	Yes, can become slimy	Yes, can get too thick
Flavor Profile	Neutral	Neutral	Neutral	Neutral

Conclusion: Finding the Right Path for Your Keto Goals

For anyone committed to a ketogenic lifestyle, is cornstarch ok on a keto diet? The simple and direct answer is no. Its high concentration of pure starch and zero fiber content make it a primary offender for disrupting ketosis and raising blood sugar levels. Fortunately, the culinary world offers a range of effective and keto-compliant alternatives that perform the same function without compromising your dietary goals. By swapping cornstarch for thickeners like xanthan gum, guar gum, or glucomannan, you can enjoy delicious, perfectly thickened sauces, soups, and desserts while staying firmly in ketosis. The key is to understand the properties of these alternatives and experiment with them to find the perfect fit for your recipes. The result is a more healthful and sustainable approach to cooking on a keto diet.

Frequently Asked Questions

One tablespoon of cornstarch contains approximately 7 grams of pure carbohydrates, making it unsuitable for the strict carb limits of a keto diet.

Xanthan gum is one of the best zero-carb alternatives. It is a highly potent thickening agent, so only a small amount is needed for most recipes.

Yes, even a small amount can be enough to disrupt ketosis. For example, two tablespoons could use up a significant portion of your daily carb limit.

Yes, a small amount of almond flour can be used, but it works differently than cornstarch and may alter the flavor. It absorbs moisture to thicken rather than creating a gel.

Glucomannan is a dietary fiber from the konjac plant that has zero net carbs. You should use it sparingly and mix it into liquid with plenty of water to prevent clumping and ensure smooth thickening.

Both are excellent low-carb thickeners. Xanthan gum is generally more potent and better for a wider range of applications, including cold foods, while guar gum is also effective but can be prone to sliminess if used in excess.

For soups and gravies, you can use heavy cream, cheese, or low-carb powders like xanthan gum or glucomannan. Glucomannan is particularly effective for sauces that need a more classic, non-dairy texture.