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French fries in any form aren't exactly a health food, but as a new study in the Proceedings of the National Academy of Sciences shows those that come from the big national fast food chains are generally less healthy than those coming from independent restaurants. It all comes down to the type of oil used to fry them.

Researchers from the University of Hawaii surveyed national fast food chains and found that 70% of the big guys (McDonald's, Wendy's, etc.) used corn oil blends for making their french fries, while only 20% of independents did so.

The big deal with corn oil is, as the report authors put it, "Corn oil contains considerably more heart-harmful saturated far than canola, sunflower, or safflower oil, and less heart-protective alphalinolenic acid than soybean oil, making it the least healthy choice" of the oils surveyed.

The interesting part, from a keeping track of big-agriculture perspective, is that corn oil is more expensive than the some of the alternatives--$70 for 32 pounds of the stuff, versus $50 for more healthy soybean oil--so some sort of deal has to be going on for this to work out in terms of cost.

The authors speculate that "it is probably necessary to contract ingredients on a large scale from preferred distributors...large scale corporate agreements are necessary to make corn oil frying cost-effective."

So, the take away: If you need to get a french fry fix, your local restaurant's are the healthier bet if you're eating out. Making your own is probably even better--all the effort needed to make them will remind you that you probably shouldn't be eating them all the time.