Boiled sweet corn has a glycemic index of about 52 to 55 on average, at the top of the low band and lower than many people assume for a starchy vegetable. It's often grouped with high-GI starches like white rice or potatoes, but the whole kernel digests more slowly than those do. Portion still matters, because corn is one of the starchier vegetables.
The numbers
The international GI tables average sweet corn at 52 (52 ± 5 in the 2008 tables), and individual tests run from about 48 to the low 60s, which reflects real variation by variety and growing conditions, not an error in any one study. This site uses 55 as a working figure, the same value in our GI vs. GL chart, where you can see corn next to rice and potatoes.
For the glycemic load, a cup of kernels (about 164 grams) has roughly 30 grams of available carbohydrate: 55 × 30 ÷ 100 ≈ 17, a medium glycemic load. A half-cup side has about 15 grams: 55 × 15 ÷ 100 ≈ 8, a low load. For why the load matters more than the index here, see how glycemic load works, or run your own portion in the glycemic load calculator.
Sources: Atkinson, Foster-Powell and Brand-Miller, International tables of glycemic index and glycemic load values: 2008, Diabetes Care (sweet corn 52 ± 5); tested entries in the University of Sydney GI database; carbohydrate per cup from USDA FoodData Central.
Fresh, frozen, canned or creamed: does the form matter?
Plain corn is the same kernel whether it comes on the cob, out of a freezer bag or from a can. What changes from form to form is what gets added. Published GI tests for frozen, canned and creamed corn as separate products are scarce, so rather than guess at numbers, use the label:
| Form | What changes | What to check on the label |
|---|---|---|
| On the cob or fresh kernels, boiled or steamed | Nothing added; this is the form behind the published GI | No label; portion is the lever (one ear or a half cup of kernels) |
| Plain frozen kernels | Blanched and frozen; same kernel | Ingredients should list corn only. Butter sauces and seasoning blends add fat, salt and sometimes sugar |
| Canned in water | Cooked in the can; close to cooked fresh corn | Added sugars (should be 0 g) and total carbohydrate per serving |
| Creamed corn or corn canned with sugar | Added sugar and starch thickeners raise the carbohydrate per serving | Total carbohydrate and added sugars; compare with a plain can |
Comparing the "Total Carbohydrate" and "Added Sugars" lines across two cans tells you more about the load than the form name on the front.
Why corn isn't as bad as its reputation
Corn gets lumped in with white rice and potatoes as a generic "starchy carb," but it tests meaningfully lower than either on average. The kernel's outer layer and fiber content slow digestion more than the processed starch in rice or mashed potatoes does. That doesn't make corn a free food: it's still one of the starchier vegetables, and a large portion adds up. But the plain, whole-kernel form (corn on the cob, or plain frozen or canned kernels) is a more moderate choice than its reputation suggests.
Corn and prediabetes
The numbers are the same with prediabetes: a GI in the mid-50s, a low load for a half cup and a medium load for a full cup. A side portion of plain corn fits most plates, especially next to a protein and a non-starchy vegetable. Whether lower-GI choices can move prediabetes back toward normal is a bigger question; we look at the evidence in can low-GI foods reverse prediabetes?
Corn on the cob or plain kernels (fresh, frozen, or canned without added sugar) are the steadier choices. Creamed corn and corn-based snacks like chips are further from the whole kernel, so check their labels before assuming they behave the same way.
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Canned and frozen corn products vary in added sugar and sauce, which changes the total glycemic load. Glycemic Genius reads the nutrition facts panel on your specific product and returns an AI estimate of GI and glycemic load on the spot. That estimate helps you compare products; it isn't a lab GI test. For the difference, see how an AI glycemic index scanner works, and our comparison of glycemic index apps for more.