Objective: To compare the effects of a rapeseed oil-based diet containing an increased proportion of easily oxidised polyunsaturated fatty acids such as alpha-linolenic acid with a diet rich in saturated fatty acids on the degree of lipid peroxidation in the human body.
Design: A randomised cross-over study.
Subjects and interventions: Nineteen healthy moderately hyperlipidemic subjects (six women and 13 men, age 50+/-8 y and body mass index (BMI) 24.5+/-2.6 kg/m(2)) were given a rapeseed oil-based diet (RO) and a control diet (SAT) rich in saturated fatty acids during two consecutive 4 week periods separated by a 4 week wash-out period. Biomarkers of lipid peroxidation and antioxidants were analysed in plasma and urine.
Results: No significant differences in plasma or urinary levels of free 8-iso-prostaglandin F(2alpha), plasma total 8-iso-prostaglandin F(2alpha) plasma hydroperoxides or plasma malondialdehyde were observed between the RO and SAT diets (P=0.14-0.95). A higher concentration of serum gamma-tocopherol was detected after the RO diet compared to the SAT diet (P<0.001), whereas the serum alpha-tocopherol concentration and plasma antioxidative capacity did not differ between the two test diets. The total cholesterol, LDL cholesterol and LDL/HDL ratio were lower after the RO diet compared to the SAT diet (P<0.001), while HDL cholesterol and total triglyceride levels were similar after the two diets.
Conclusion: These results suggest that a rapeseed oil-based diet rich in alpha-linolenic acid does not seem to increase the degree of lipid peroxidation in plasma and urine compared to a diet rich in saturated fats. This is possibly due to a sufficient content of antioxidants in the rapeseed oil diet to increase circulating concentrations of antioxidants that may protect unsaturated fatty acids from oxidation.
Sponsorship: Swedish Council for Forestry and Agricultural Research and Foundation for Geriatric Research.