Margarine Misgivings

• Share

Not long ago, ordering margarine with your toast seemed like a downright virtuous thing to do. Without all the saturated fats that plump up butter, margarine was said to be the perfect way to get flavor without endangering your heart. In recent years, however, evidence has mounted that this supposedly healthier spread poses cardiac risks of its own. And last week a study in the New England Journal of Medicine suggested that those risks are so great that it may be time to consider modifying food labels so consumers can tell which butter substitutes are good for them and which are not so good.

The problem with margarine comes from substances known as trans-fatty acids. At room temperature, the vegetable oil used to make margarine and shortenings stays in a liquid state, not the most spreadable consistency. When the oil is treated with heat and chemicals, the fatty-acid molecules straighten out, allowing the liquid to solidify. But this trans-fatty configuration also converts beneficial polyunsaturates into less healthy fatty acids, and this can cause blood fats to rise.

Just how high they rise was made clearer than ever last week. In a study conducted at Boston's Tufts University, researchers fed subjects randomly selected diets that included soybean oil, semiliquid margarine, soft margarine, shortening and stick margarine, and then compared their blood fats to levels measured in high-butter diets. The more trans-fatty acids in a spread, scientists found, the more fats in the blood. Although all the butter substitutes reduced the level of LDL (the "bad" cholesterol), the trans-fatty acids sometimes drove down the concentration of HDL ("good" cholesterol), changing the critical ratio of total blood cholesterol to HDL. In the case of stick margarine, this ratio actually climbed above the butter baseline. Says Tufts professor of nutrition Alice Lichtenstein, who headed the study: "It's the stick margarine, with its high trans-fatty-acid content, that is the worst offender."

Any other food that failed so conspicuously to live up to its good-for-you hype would be required to admit that fact, and the Journal argued that margarine should be treated no differently. In an editorial accompanying the study, researchers insisted that not only should margarine products be required to disclose their trans-fatty-acid content but so too should fried fast foods like French fries, which account for up to 75% of the trans-fatty acids consumed--often unknowingly--in the U.S. each year.

None of this argues for a return to an all-butter diet. Margarines may not lower LDL levels much, but lower them they do. What's more, food scientists in Europe have developed margarines free of trans-fatty acids, and these are slowly making their way to grocery shelves in the U.S. Until they're in wide use here, it's up to manufacturers to give consumers the food labels they need--and it's up to consumers to read them.