Dietary intakes of polyunsaturated fatty acids and indices of oxidative stress in human volunteers

Objective: To assess whether nutritionally-relevant changes in polyunsatura ted fatty acid (PUFA) intake alter indices of oxidative stress in human vol unteers Design: A split plot/change over dietary study where half the volunteers co nsumed a diet containing 5% PUFA (low PUFA) as food energy for 4 weeks and after a 6 week washout period consumed a 15% PUFA (high PUFA) diet for anot her 4 weeks. The second group of volunteers completed this protocol in reve rse. Total fat, carbohydrate, protein and vitamin E contents of the diets w ere constant. Subjects: 10 healthy, non-smoking, male volunteers aged 32.6 +/- 1.7y Results: There was a significant increase in whole blood oxidised glutathio ne (P < 0.05), an index of oxidative stress, after consumption of the high PUFA diet. Moreover, urinary thiobarbituric acid reactive substances (TBARS ), an index of lipid peroxidation, significantly increased (P = 0.038) foll owing consumption of the high PUFA diet and decreased (P = 0.031) after con suming the low PUFA diet. However, there was no change in nan specific plas ma indices of lipid peroxidation, conjugated dienes and TEARS, nor in red c ell antioxidant enzymes glutathione peroxidase, glutathione reductase, and catalase. However, superoxide dismutase significantly decreased (13%, P = 0 .018) after consumption of the low PUFA diet. Total cholesterol increased b y 13% (P = 0.014) after consumption of the low PUFA diet. Conclusions: This study indicates that although increasing dietary levels o f PUFA may favourably alter cholesterol profiles, the same dietary changes may adversely affect some indices of lipid peroxidation. Care should be tak en when providing dietary advice on PUFA intake and an adequate intake of a ntioxidants to match any increased PUFA may be important for preventing oxi dative stress.