If you want to be green, you'll find there are plenty of GMO-free foods to choose from for your refrigerator, but when it comes to avoiding Monsanto's (MON) drive to monopolize the world's seed market with its genetically modified Roundup Ready seeds, there's actually a dearth of GMO-free stocks to invest in.

Whole Foods Market (WFM) may be the closest place investors can readily turn to, and it is leading the drive for mandatory labeling of GM products (though some complain its five-year timeline amounts to glacial foot-dragging). Tea maker Hain Celestial (HAIN 3.47%) is another, as it strives to maintain GMO-free blends.

And that's about where the purity list ends for publicly traded companies.

Guilt by association
Dairy farmer WhiteWave uses non-GMO soybeans in its Alpro and Silk soy milks, but its Land O'Lakes brand comes from a company of the same name whose Forage Genetics subsidiary is a partner with Monsanto in the development of Roundup Ready alfalfa seeds.

And while we can point to various brands like Kashi that are verified non-GMO, its owner Kellogg makes no such assurances about its Corn Flakes or Frosted Flakes. Sure, it's difficult to be pure when nearly 90% of the U.S. corn crop has been messed with by scientists, and though we might want to buy Kashi cereals to eat, we may find investing in its parent hard to swallow if we want to be consistent.

And even then Kashi admits it can't fully guarantee all of its products haven't been cross-pollinated by GMO crops. Two fields planted side by side, one GMO the other GMO-free, will result in the natural crops getting polluted with the altered traits due to cross-pollination.

Several court cases have dealt with farmers who were being sued by Monsanto because they claim the agri-giant's crops cross-pollinated their own. Thus far the courts haven't bought into those defenses yet, and the Supreme Court recently agreed that Monsanto seed patent protection extends for all time as the seeds propagate.

So with its patents intact and the high possibility of cross-contamination occurring, the ability to maintain a pure seed strain unaffected by Monsanto's meddling becomes more difficult. And finding companies that can keep up the pretense of purity becomes more challenging as well.

Heck, Monsanto's pervasiveness is such that even Whole Foods can't guarantee all the products it sells are GMO-free. It's certainly committed to identifying foods that have had their genetic code messed with, but without a labeling requirement, not even it can say with certainty its products are free from contamination.

The synthetic trinity
Together, Monsanto, DuPont (DD), and Syngenta control 53% of the world's seed production, yet their reach is far greater as they sign cross-licensing agreements with other companies. Monsanto recently hooked up with Dow Chemical (DOW) and Bayer to have its technology embedded in their products.

Both Syngenta and DuPont have responded in kind, and in fact, DuPont and BASF first sued each other before realizing they could spread further by cross-licensing their respective technologies instead. DuPont did the same thing with Monsanto, too.

The food chain has become increasingly proliferated with genetically modified food to the point that we have no idea what we're even eating. Just adding sugar to your coffee increases the likelihood you're ingesting GMO-stained sweetness. While 45% of the U.S. sugar market is derived from sugar cane (and thus far not contaminated with genetic modification), the other 55% of it comes from sugar beets, and 95% of that crop is grown from Monsanto's GMO seeds.

Needle in a haystack
Thus it's left for investors who want to support the non-GMO trend to determine the level of purity (or lack thereof) they're willing to accept. Whole Foods likely sells some GMO foods in its aisles, but would prevent it if only it knew what was in the products it offered. The company would probably get a pass from most investors, but would Kellogg similarly get the nod simply because it owned Kashi, even though its full portfolio of cereals is laden with GM grains? Or would WhiteWave get the green light despite a licensed brand being associated with creating GMO-laced alfalfa? Doubtful.

It remains true today that the best way to protect yourself from "Monsanto creep" is to start your own garden and plant heirloom seeds. Protecting your portfolio, however, is not so simple, and avoiding a surefire winner like the agri-giant could end up being hazardous to your financial health.

So let me know in the comments section below what companies you believe are worth investing in from a non-GMO perspective.