['Replacing saturated fat with polyunsaturated fat reduces plasma cholesterol concentrations; however, it has not been well documented how rapidly the decline occurs nor how long is required to reach the maximum cholesterol-lowering effect. The aim of the present study was to determine the time course of change in plasma cholesterol concentrations when participants adopt a lipid-lowering diet.', 'Participants (n = 19) were asked to follow for 19 days a diet high in saturated fat and then crossed over--without washout--for 19 days to a diet high in n-6 polyunsaturated fat. Participants were asked to maintain a total fat intake of 30-33% of total energy on both diets. Energy and nutrient intakes were assessed by self-reported food records covering 3 days. Plasma total cholesterol concentrations were measured on days 0, 1, 2, 5, 8, 12, and 19 of the n-6 polyunsaturated fat rich diet. Mean (95% CI) plasma total cholesterol concentration declined from 5.10 mmol/L (4.77, 5.46) at day 0 to 4.25 mmol/L (3.83, 4.67) on day 12 and remained unchanged at 4.23 mmol/L (3.85, 4.61) on day 19. A statistically significant decrease in plasma cholesterol concentration was achieved on day 2 of the intervention; by day 5, 59% (0.51 mmol/L) of the maximum reduction (0.87 mmol/L) had been reached.'] Is maximal response to a plasma cholesterol-lowering diet achieved within two weeks?