Advice should now be to increase intake of vegetable oils and fish

EDITOR—The systematic review by Tang et al analysed the effect of various diets, particularly the American Heart Association step 1 and step 2 diets, on reducing total blood cholesterol concentration.1 Overall, the effect of diet on blood cholesterol concentrations in free-living communities was no more than about 6%, with step 1 diets achieving a 3% reduction and diets that increase the ratio of polyunsaturated to saturated fatty acids around an 8% fall.

The effect of diet on coronary heart disease rates is complementary.2 In six primary prevention trials of low fat and low cholesterol diets the odds ratio for death from coronary heart disease was 1.04 (95% confidence interval 0.43 to 2.06) and for non-fatal events 1.05 (0.46 to 2.98); in two secondary prevention trials with a similar regimen the respective odds ratios were 1.21 (0.66 to 1.78) and 1.00 (0.76 to 1.37).

Four secondary prevention trials increased the ratio …