Cornstarch is starch derived from the endosperm of the corn kernel. Since corn is not Paleo, we can’t include cornstarch. It’s pure carbohydrates without much nutrients. The Paleo diet is nutrient-dense above all, and usually pretty low-carb. Cornstarch violates both of these requirements, which is why it’s not considered Paleo.
Paleo and Autoimmune Protocol
Cornstarch is commonly used as a thickener, especially in sauces. It’s usually used in such small amounts that it’s not a problem for most of us, but it is a grain and it does contain antinutrients. Those antinutrients can cause plenty of problems in some people, including inflammation and digestive problems, even when used in small amounts.
If you’re trying to create a truly Paleo sauce, Mark Sisson has a number of Paleo-friendly tips for thickening your sauces.