Top Five Unnatural Foods: Clone Burgers Not yet on List

Green groups gagged when the U.S. Department of Agriculture recently declared meat from cloned animals to be safe for human consumption, but clone-burgers wouldn't be the first taste of unnatural food for most of us.

So what other, not-found-in-nature foods can you find in your supermarket? Consider these:

1. Genetically modified papayas, flax and soy. Genetically modified, or GM, foods come from plants that have had genes from other species spliced into them. Some GM crops are created to be more pesticide- or drought-resistant, while others might eventually be made to have super-levels of vitamins or other nutrients. Most of the soybeans and nearly half of the corn grown in the U.S. is GM., though much of that is used for livestock feed. If you've bought papayas from Hawaii or canola, though, chances are good you've eaten GM food. (By the way, here's a tip for evaluating produce: if the little sticker on your squash or zucchini starts with an 8, the food is GM; a 9 at the beginning indicates organic produce, while a 4 means it's conventionally grown.)

2. High-fructose corn syrup. Found in soda, junk food and processed foods of all kinds, high-fructose corn syrup (HFCS) is kind of like corn syrup on steroids. While not technically "unnatural" -- it is made from corn syrup, after all -- HFCS is made via enzymatic processing to boost the natural syrup's fructose content. HFCS didn't exist before 1957 (the year the process for making it was invented), but it's taken off big-time since then, in part because it's cheaper than sugar and in part because it helps foods last longer.

3. Irradiated foods. The U.S. Food and Drug Administration allows certain foods -- some meats, for example -- to be zapped with high-energy gamma rays, x-rays or electron beams that kill parasites and bacteria. The treatment doesn't leave your food radioactive, but opponents say it reduces vitamin content.

4. Beef a la CO2. Exposed to regular air, ground beef soon turns from a fresh-looking red to a less-appetizing brown. That's why many food retailers package their meat in a mix of carbon dioxide and nitrogen (and, sometimes, a little carbon monoxide as well): the special atmosphere keeps the ground beef looking shopper-friendly "fresh."

5. The Twinkie. Of course, we all know the Twinkie isn't natural. But, in his 2007 book, "Twinkie, Deconstructed," author Steve Ettlinger explores in depth just how not-natural the spongy treat with a cream filling is. The small amount of ferrous sulfate in each snack cake, for example, originates from iron ore mines and steel mills, while the cellulose gum comes from trees or cotton. As for the flavors and colors? Well, the adjective "artificial" in front of both those words on the label says it all.