The effect of a low-cholesterol, high-polyunsaturate diet on serum lipid levels, apolipoprotein B levels and triglyceride fatty acid composition

1. (1) Seven healthy normolipaemic men aged 28–46 years (mean 33 years) were studied for four weeks on their usual diet, the mean polyunsaturated to saturated fat (P : S) ratio of which was approximately 0.23 and the cholesterol content 667 mg/day, and for four weeks on an isocaloric diet, containing similar proportions of protein, carbohydrate and fat, but with a mean P : S ratio of approximately 2.82 and a cholesterol content of 112 mg/day. 2. (2) Total serum cholesterol levels decreased by 18.7 ± 5.2% (mean ± SEM) on the polyunsaturated fat (PUF) diet. This was attributable to a similar reduction in serum low density lipoprotein (LDL) cholesterol. Serum very low density lipoprotein (VLDL) cholesterol showed no clear change. Total serum triglyceride levels decreased by 19.7 ± 7.1% due to a reduction in both serum VLDL and LDL triglyceride concentration. 3. (3) Total serum apolipoprotein B concentration fell by 23 ± 2.6% during the PUF diet. There was a decrease of similar magnitude in serum LDL apolipoprotein B, but no sustained effect on serum VLDL apolipoprotein B. 4. (4) Serum VLDL and LDL lipid to apolipoprotein B ratios did not change significantly during the study. 5. (5) Serum triglyceride fatty acid composition significantly altered during the PUF diet. The percentage of linoleic acid rose from 16 ± 0.90% to 36 ± 0.89%, whilst the percentage of combined saturated and monounsaturated acids fell correspondingly. These changes took place within 2 days of starting the PUF diet.