Eat something with high fructose corn syrup as an ingredient, and chances are you're gobbling GMOs. Even fresh tomatoes, if not certified organic, hold the possibility of being genetically altered. As long as you know this going into the store, you can at least make an educated guess whether you're eating GMOs.

But what about the vitamins and supplements you take every day? You might think your horse chestnut tablet is as pure as the plant it was wildcrafted from, but GMO soy may have been used as an inactive ingredient to coat and hold the tablet together. Trouble is, most soy comes from the United States, and much of that has been genetically engineered to resist herbicides.

"It's very hard to find any soy that's certified GMO-free," says Eileen Sheets of Bioforce, a Swiss supplements manufacturer.

In 1988, California supplement maker Rainbow Light DNA-tested their soy raw material and found GMO levels ranging from 5 percent to 40 percent. Since then, they have converted their formulas to contain less than 1 percent GMOs, which is generally considered as low as tested levels realistically get.

Still, many manufacturers are not concerned with the miniscule levels of GMOs that may comprise pills but aren't considered active ingredients. Are you?