The Women’s Health Initiative is one of the largest randomized controlled diet trials ever performed using 48,835 post-menopausal women, with a mean follow-up period of 8.1 years, randomized to either a standard western diet or a low-fat, calorie-reduced diet with increased exercise.

The authors had postulated that a low-fat, calorie-reduced diet with increased exercise would reduce cardiovascular disease. The intervention achieved an 8.2% energy decrease in total fat intake and a 2.9% energy decrease in the saturated fat intake but did not reduce the risk of CHD or stroke.

The reduction in dietary fat and total daily calories (361 calories/day reduction) failed to produce any significant weight loss over the duration of the study, rejected the hypothesis that the low-fat diet is either beneficial for cardiovascular disease or weight loss.