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

OBJECTIVE

To assess whether nutritionally-relevant changes in polyunsaturated fatty acid (PUFA) intake alter indices of oxidative stress in human volunteers

DESIGN

A split plot/change over dietary study where half the volunteers consumed 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 another 4 weeks. The second group of volunteers completed this protocol in reverse. Total fat, carbohydrate, protein and vitamin E contents of the diets were constant.

SUBJECTS

10 healthy, non-smoking, male volunteers aged 32.6 +/- 1.7 y

RESULTS

There was a significant increase in whole blood oxidised glutathione (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) following consumption of the high PUFA diet and decreased (P = 0.031) after consuming the low PUFA diet. However, there was no change in non specific plasma indices of lipid peroxidation, conjugated dienes and TBARS, nor in red cell 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 by 13% (P=0.014) after consumption of the low PUFA diet.

CONCLUSIONS

This study indicates that although increasing dietary levels of PUFA may favourably alter cholesterol profiles, the same dietary changes may adversely affect some indices of lipid peroxidation. Care should be taken when providing dietary advice on PUFA intake and an adequate intake of antioxidants to match any increased PUFA may be important for preventing oxidative stress.