Dietary fat saturation and gender/hormonal status modulate plasma lipids and lipoprotein composition(1)

Male, female and ovariectomized (to mimic menopause) guinea pigs were fed a saturated (SFA) or a polyunsaturated (PUFA) fat diet for 4 weeks to determine the effects of dietary fat saturation on lipoprotein levels and composition and to assess whether gender and hormonal status modulate the cholesterolemic response. Both diets contained 15g/100 g fat and 0.04 g/100 g cholesterol and were identical in composition except for the type of fat. The SFA diet contained 50% saturated fat (25% lauric + myristic fatty acids), 25% PUFA and 25% monounsaturated fatty acids while the PUFA diet had 50% PUFA (linoleic acid), 25% monounsaturated and 25% SFA fatty acids. Plasma LDL cholesterol (LDL-C) was an average 21% lower in guinea pigs fed PUFA compared to those fed SFA (P < 0.05). In addition, ovariectomized guinea pigs, both in the SFA and PUFA groups, had 20-33% higher LDL-C than either males or females (P < 0.01). VLDL cholesterol was 70% higher in the PUFA-fed animals (P < 0.0001). A gender effect was observed in plasma HDL cholesterol (HDL-C) with females and ovariectomized guinea pigs having 30-42% higher HDL-C than males (P < 0.01). LDL susceptibility to oxidation was not affected by dietary fat saturation or gender. In contrast, VLDL and LDL composition were significantly influenced by diet and gender. VLDL particles were larger in size in guinea pigs fed the SFA diets (P < 0.01) while LDL particles were larger in female guinea pigs (P < 0.001). Hepatic lipids were influenced by the interaction between diet and group. Hepatic cholesterol (P < 0.01) and TAG concentrations (P < 0.0001) were highest in female guinea pigs fed the PUFA diet. Since the liver is the major site of lipoprotein synthesis and catabolism, these results suggest that not only diet but also gender may play a major role in determining the composition and size of lipoproteins.