Plasma thyroxine and cholesterol concentrations of miniature pigs are influenced by thermally oxidized dietary lipids

To investigate the effect of a dietary oxidized oil on thyroid hormone stat us and circulating cholesterol, we conducted a study with 16 male miniature pigs fed a nutritionally adequate diet with 15% of either fresh or thermox idized oil for 35 d (n = 8/group). The thermoxidized oil was prepared by he ating sunflower oil at 110 degrees C for 48 h. The fresh oil consisted of a mixture of sunflower oil and lard (94:6, v/v) which had a fatty acid compo sition similar to the thermoxidized oil. At the end of the study, there wer e no differences in body weight gains and plasma clinicochemical variables between groups, suggesting that the thermoxidized oil did not induce genera l toxic symptoms. However, pigs fed the thermoxidized oil had significantly higher plasma concentrations of total and free thyroxine (P < 0.05) and a tendency for a higher plasma concentration of thyroid hormone-stimulating h ormone (P < 0.1) than pigs fed the fresh oil. Additionally, pigs fed the th ermoxidized oil had lower concentrations of cholesterol in plasma, LDL and HDL (P < 0.05), There were significant negative correlations between the pl asma concentrations of total (r = -0.29) and free thyroxine (r = -0.40) and that of cholesterol (P < 0.05), suggesting that there is a causal relation ship between the changes in thyroxine concentration and the reduction of pl asma cholesterol, Our results indicate that there is a close relationship b etween alterations of thyroid hormone status and cholesterol metabolism in pigs fed a thermoxidized oil, and dietary oxidized fats should be considere d in thyroid hormone disorders.