So how do you know what products contain GMOs at your local grocery store? Well, since the FDA doesn’t require the labeling of foods that contain GMOs, it takes some detective work.

Several natural products retailers are taking the matter into their own hands—such as Mile High Organics of Colorado, who have gone all out to ensure that the products they sell are 100 percent GMO-free.

“I don’t believe that consumers should be deceived,” Michael Joseph, founder and CEO of Mile High Organics, says. “I don’t consider that the US government is doing a good job of protecting its citizenry, and some retailers are starting to step up and have done very well at educating their consumers. We really have found a strong and loyal consumer base that believes exactly the same thing, and people have thanked us. I’ve had people tell me that they think I’m essentially doing work that should be done by the government.”

But if you don’t have a store such as this in your hood, here’s some help to playing GMO detective:

Look for the Non-GMO Project seal. A third-party verified seal means that a product has been produced according to rigorous best practices for GMO avoidance, including testing of risk ingredients. The Non-GMO Project also offers a searchable database of non-GMO products on its website.

This iPhone app, shopnogmo, is a great in-store resource for filling your cart with non-GMO items.

Ask vendors at your farmers’ markets if they use GMO technology.

Certified organic foods are required to be non-GMO. In the absence of government-required GMO labels, certified organic products are a good non-GMO guideline. Non-GMO Project labels give even more assurance, as the product has been specifically tested to confirm no GMOs.

The Institute for Responsible Technology offers a phone app for non-GMO shopping and other non-GMO shopping resources.

Corn is present in most processed foods, so avoid these unless certified organic and non-GMO.

Download the Center for Food Safety’s NEW True Food Shopper’s Guide to avoiding GE foods.