How Healthy Are McDonald's Fries?

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n as a doctor, I sometimes have difficulty remembering which are the good fatty acids and which are the bad. So when McDonald's announced last week that it was changing its cooking oil — reducing trans-fatty acids 48% and increasing polyunsaturated fats 167%--I had to pull out an old textbook to make sure this was a good thing. It turns out it is. And more important, it's a step in the right direction for the fast-food industry.

McDonald's, Burger King and the rest rely heavily on fatty acids to fry their wares. This is not entirely bad. Fatty acids are the building blocks of dietary fats, an essential part of the human diet. Dietary fats contain a mixture of saturated and unsaturated fatty acids (the difference: saturated fats carry a full quota of hydrogen atoms in their chemical structure, and unsaturated fats do not). Such products as tallow, lard and butter are saturated fats, whereas those like soybean, canola, olive, cottonseed, corn and other vegetable oils are unsaturated. Saturated fats are associated with increases in ldl cholesterol (the bad kind); unsaturated fats can bring that number down.

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It gets a little confusing when you start talking about trans-fatty acids. In the old days, fast-food fried products were cooked primarily in animal fats, which are generally saturated and bad for your heart. Under pressure from consumers, many fast-food chains switched to unsaturated vegetable oils.

But vegetable oils tend to be less stable and turn rancid more quickly than animal fats. So many outlets switched again, turning to vegetable oils that have been hydrogenated — a process that fills open slots in unsaturated fat molecules with hydrogen atoms, allowing vegetable oils to stay fresh longer while still cooking up fries that are crisp and tasty.

For the fast-food industry, these partially hydrogenated oils were doubly beneficial: the companies got a cheap product with a long shelf life while giving customers the vegetable oils they demanded, albeit hydrogenated ones. For the eating public, however, the result was quite the opposite. That's because hydrogenated fats contain a kind of hydrogen bond called trans that is as bad as the hydrogen bond in saturated fats — maybe even worse, according to CNN dietitian Liz Weiss, an expert on family nutrition. While saturated fats raise ldl cholesterol, Weiss explains, "trans fats appear to both raise bad (LDL) cholesterol and lower the good (HDL) cholesterol." The FDA does not currently require vendors to label foods for trans-fatty-acid content, but the agency has new rules in the works that would force McDonald's and others to do just that.

McDonald's oil change will make its fried foods — including French fries, Chicken McNuggets and Filet-O-Fish — better for the hearts of the 46 million customers who eat there every day, but it will not turn any of those dishes into health foods. Fries cooked in the new oil will have precisely the same caloric content and will do nothing to trim America's growing waistline. So eat fries from time to time if you must, but don't supersize them. Better still, try the salads.

Dr. Gupta is a neurosurgeon and CNN medical correspondent