Should you be choosing butter over margarine? (trans fatty acids and blood cholesterol)

Should you be choosing butter over margarine? Americans ate 43 percent less butter last year than they did in 1961, at least in part because they are heeding the message that the saturated fat in butter is worse for the heart than the unsaturated fat in, say, margarine. But a widely publicized study generating headlines like "Margarine, too, is found to have the fat that adds to heart risk" has led some people to begin questioning the wisdom of giving up butter and using margarine instead. The new report suggests that margarine contains fats that raise blood cholesterol at least as much as the saturated fat in butter does.

The fats in question are formed during …