Serum concentration and metabolism of cholesterol during rapeseed oil and squalene feeding

The effect of rapeseed oil with and without added squalene was studied on serum lipids and cholesterol metabolism. Dietary rapeseed oil reduced LDL cholesterol by 10%, increased cholesterol precursors and plant sterols, and decreased cholestanol in serum during a 6-wk baseline period from initial values. Addition of 1 g squalene in rapeseed oil for 9 wk caused net increases in serum total, VLDL-, IDL-, and LDL-cholesterol concentrations by 12%, 34%, 28%, and 12%, respectively; squalene by five times; and cholesterol precursor sterols by up to 60%. Fecal squalene was 15% of the dietary intake, cholesterol absorption was unchanged, fecal neutral sterols were significantly increased, whereas, in contrast to the precursor sterols, the increase in cholesterol synthesis was insignificant. LDL apolipoprotein B was increased by 14% with unchanged removal but enhanced transport of LDL apolipoprotein B. A negative correlation between the changes in LDL apolipoprotein B removal and LDL cholesterol suggests that LDL receptor activity was down-regulated, allowing more of the LDL precursor lipoproteins to be converted to LDL. A subsequent 6-wk period on 0.5 g squalene/d normalized serum sterols.