Butter lovers: the news isn't all bad.

For years, studies conducted at the Human Nutrition Research Center have been showing that reducing dietary fat will lower blood pressure. And, says Joseph Judd, supervisory research chemist at the center's Lipid Nutrition Laboratory, that should be good news for the estimated 25 million people in the United States whose mildly elevated blood pressure appears to predispose them to clinical hypertension (high blood pressure) -- a risk factor in heart disease, kidney disease and stroke. But most of those people seem to have resisted making the dietary change this research would recommend. And no wonder, notes Walter MErtz, the center's director: "The problem with fat is that it tastes so good." So Judd and his colleagues decided to investigate whether, in order to lower blood pressure, fat-lovers had to cut down on all forms, or might instead get by with substituting more polyunsaturated fats, like safflower oils, for the butter they loved.

The bad news is that the new research continues to show "a very strong effect of dietary fat on blood pressure," Judd says. The good news for butter lvoers is that saturated fats appear to be no worse than polyunsaturates -- at least as far as blood pressure is concerned. The data come from a series of studies involving 16 to 30 volunteers who, while living at home and working as usual, for 12 weeks ate only meals and snacks provided by the lipid lab.

The most conclusive data, explains nutritionist mary Marshall, came from a study where all the participants ate two low-fat diets -- each having only 25 percent of its calories derived from fat. For six weeks, half ate a diet in which the polyunsaturated-to-saturated fat ratio was 1:1, the others a diet in which the ratio was approximately 1:3 -- meaning it was higher in saturated fats (mainly butterfat) but not in cholesterol. After six weeks, the groups swapped diets.

Both low-fat diets brought equivalent declines in blood pressure--on average, a 6 percent decline from baseline readings recorded in the participants during the five weeks immediately preceding and succeeding the 12-week test period.

"While those may seem like small changes," Marshall told SCIENCE NEWS, "to drop like that and remain stable over a period of 12 weeks, and then climb back up [once participants returned to their normal diets], is significant."