It is more important to increase the intake of unsaturated fats than to decrease the intake of saturated fats:...

The evidence from formal, controlled, long-term clinical trials that changes in dietary fats reduce the incidence of ischemic (coronary) heart disease (IHD) is unimpressive. Mostly these trials were underpowered and in several the rigor of dietary control in the intervention and control groups was inadequate. Six controlled clinical trials in healthy people of diets low in saturated fat and cholesterol, also accompanied by changes in other risk factors, were unsuccessful in reducing the incidence of IHD. An exception was the Oslo trial in which concurrent cigarette smoking was almost halved. Similarly, in the only two clinical trials of the secondary prevention of IHD through use of diets low in saturated fats and cholesterol there was no significant effect on IHD recurrence rate. This may relate to poor compliance outside strict clinic conditions. In contrast, five of six secondary prevention trials in which diets low in saturated fats were supplemented with polyunsaturated fats reduced IHD deaths and, to a lesser extent, all-cause mortality. No formal trial has been reported of the effects on IHD of diets high in monounsaturated fats. The greatest benefit for patients with IHD has come from diets supplemented with n-3 fatty acids (two trials), and this benefit was independent of changes in plasma lipoproteins. The evidence from these clinical trials indicates that more emphasis should be given in national and international dietary recommendations to supplementation with polyunsaturated fats, particularly foods rich in n-3 fatty acids, than to diets low in total and saturated fats.