Corn is a fundamental staple food worldwide. For individuals monitoring their intake of plant compounds, particularly those prone to forming kidney stones, the level of oxalates in this grain is a dietary concern. This analysis clarifies the varying levels of oxalates in corn and details preparation methods that influence the final concentration of this compound.
Understanding Dietary Oxalates
Oxalates, or oxalic acid, are naturally occurring organic compounds found in a wide variety of plants. Once consumed, oxalates bind with minerals, most notably calcium, within the gastrointestinal tract.
This binding process forms insoluble calcium oxalate crystals. Most of these compounds are eliminated in the stool. However, some oxalates are absorbed and excreted through the urine. When high concentrations of calcium oxalate crystals are present in the urinary tract, they can aggregate and form stones.
Quantifying Oxalate Levels in Corn
The oxalate concentration in corn products varies significantly depending on how the grain is processed. Sweet corn kernels, whether fresh or canned, are considered a low-oxalate food. A half-cup serving of cooked, drained sweet yellow corn kernels contains approximately 0.8 to 2 milligrams of oxalate.
In contrast, products made from ground, dried corn have higher levels. Cornmeal and corn grits fall into the moderate to high-oxalate categories. A half-cup serving of cooked corn grits can contain up to 49 milligrams of oxalate. Cornmeal similarly contains around 32 milligrams per half-cup serving.
These elevated levels are still far below the concentrations found in extremely high-oxalate vegetables, such as spinach or rhubarb, which can contain hundreds of milligrams per serving. For those following a low-oxalate diet, corn products like corn grits and cornmeal require careful portion control. Other common items are generally lower: a single corn tortilla contains about 7 milligrams, and a piece of cornbread contains 4 milligrams.
Preparation Methods to Minimize Oxalate Content
Certain cooking techniques can effectively reduce the amount of oxalate available for absorption. This reduction is possible because oxalates are highly water-soluble. Boiling is a particularly effective method, as a significant portion of the soluble oxalate leaches out into the cooking water.
To maximize oxalate reduction, the cooking water must be discarded rather than incorporated into the final dish. Steaming or baking is not as effective as boiling. Another traditional method, nixtamalization, involves treating the corn kernels with an alkaline solution, typically containing lime, or calcium hydroxide.
The nixtamalization process introduces calcium, which binds to oxalates within the grain. This binding forms insoluble calcium oxalate, which is then rinsed away with the cooking liquid, reducing the final oxalate load in the masa used for tortillas and tamales. Consuming corn products alongside a calcium-rich food, like dairy, can also help bind oxalates in the digestive tract, further reducing the amount absorbed by the body.