If there's one indulgence that's practically unavoidable this time of year, it may well be the tray of holiday cookies. Adorned with sprinkles, spread with jam and frosting or dusted with powdered sugar, such cookies are a far cry from a healthful snack. Still, many cooks may nonetheless stand in their kitchens and wonder: Is it better to make them with margarine or butter?
Butter and margarine have a similar overall fat content -- and therefore a lot of calories, says Katherine Zeratsky, a registered dietitian with the Mayo Clinic in Rochester, Minn. But the composition of the fats in butter and margarine differs significantly.
"You have to pick the lesser of two evils," Zeratsky says. "In butter, it's the saturated fat content, and in margarine, it's trans fat."
A tablespoon of butter contains more than three times the amount of cholesterol-raising saturated fat than the same amount of margarine -- 7 grams in butter compared with 2 grams in margarine.
In addition, butter and margarine contain mono- and polyunsaturated fats, but margarine contains them in far greater amounts: close to 9 grams per tablespoon compared with butter's 3.5 grams. These fats don't raise LDL cholesterol -- and some can help lower it, says Penny Kris-Etherton, professor of nutrition at Penn State University in University Park, Penn.
Margarine's drawback is its trans-fat content. Margarines are made from blends of vegetable oils, such as corn, soybean, safflower or canola. Hydrogenation, a chemical process, replaces double chemical bonds in those oils with single chemical bonds, making the liquid oils solid at room temperature. When that replacement process is incomplete, the result is a partially hydrogenated oil, also known as a trans fat. Trans fats are what make margarine solid instead of liquid -- but they've also been shown to be even worse for heart health than saturated fats. Not only do trans fats raise LDL cholesterol levels, they also lower HDL, or good, cholesterol.
For the last two years, manufacturers have been forced to list trans fats on food labels; as a result, many have reformulated their margarines (and other products) to lower or eliminate their trans fat content.
But the letter of the law is such that a food can claim to have no trans fat as long as it contains less than 0.5 gram of trans fat per serving. "Even when the label says trans fat-free, it doesn't really mean that," says Barry Swanson, a food science professor at Washington State University in Pullman.
Food scientists, meanwhile, are still experimenting with alternatives to trans fats, which have been put into foods since the label law, says Richard Hartel, professor of food engineering at the University of Wisconsin-Madison. Many manufacturers are replacing trans fats with a blend of vegetable fats; one common substitute is palm oil, which was condemned decades ago for its large fraction -- 50% -- of saturated fat. Today, manufacturers often alter that fraction, but the final fraction of saturated fats in margarine containing palm oil may not be discernible from the label, Swanson says.
Butter, on the other hand, is and always has been churned milk, a fact that makes it preferable to certain consumers, Zeratsky says. But that very fact means that butter, as an animal product, is loaded not only with saturated fat but also contains cholesterol -- something margarine doesn't contain.
Of course, when it comes to baking cookies, there are other factors on which to base the butter or margarine decision: aesthetics and flavor.
Butter contains an abundance of small-chain fatty acids, which readily break down during the baking process into a variety of molecules with a range of flavors -- lending baked goods a rich, buttery flavor, Swanson says. The flavor imparted by the long-chain molecules in vegetable oils, on the other hand, is far less complex.
Butter and margarine both tend to make thin, flat cookies. Though tub margarine often has more of a healthful profile than stick margarine -- it has more polyunsaturated fat and is less likely to contain trans fat -- cookies made with tub margarine will be very thin and oily due to tub margarine's high liquid content, says Eric Decker, chairman of the department of food science at the University of Massachusetts at Amherst.
Of course, sticklers for a cookie with light texture and volume know that the secret is neither butter nor margarine -- it's often shortening or lard, fat content be damned.
Hartel, author of "Food Bites: The Science of the Foods We Eat," says he uses a combination of butter and shortening when baking cookies. "Ultimately, that's a personal choice. The key is not to eat too many cookies."