Cornstarch

Cornstarch is the pure starch fraction of corn kernel — the bran, germ, and protein are washed away during processing. What remains is nearly 100% carbohydrate with essentially no fiber, fat, or protein. As a cooking ingredient it's prized for its thickening power: a tablespoon thickens a cup of liquid into a clear glossy sauce.

Blood sugar

Cornstarch has a glycemic index in the 80s — higher than table sugar. In thickened sauces or fruit fillings, the dose is usually small enough that this doesn't matter on its own. The issue is the cumulative load: most ultra-processed foods (frozen dinners, gravies, instant puddings, processed meats, breaded coatings) use cornstarch or modified cornstarch as filler, and the totals add up. People with diabetes or insulin resistance benefit more from minimizing those carriers than from worrying about a tablespoon in a stir-fry.

Modified vs. native

Most cornstarch in packaged food is "modified" — chemically or physically altered so it thickens cold liquids, survives freezing, or stays stable through industrial processing. "Modified food starch" on a label means modified cornstarch about 80% of the time in North America. It's not less safe than native cornstarch, but it's a marker of an ultra-processed product rather than a home-cooked one.

Corn-allergic people are rare, but cornstarch is corn-derived and not safe for them. Most cornstarch in the US is from genetically modified corn — relevant if GMO-avoidance is a priority, otherwise nutritionally identical.