Effect of diet and physical activity on the markers of oxidative stress
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Lifestyle diseases such as cardiovascular diseases, hypertension, cancer, type 2 diabetes are the major causes of mortality and morbidity worldwide. The prevalence of these diseases is high in New Zealand as well. It is believed that promoting a healthy diet and increased physical activity can make beneficial changes and extend the healthy life expectancy. This twelve week study with follow-up at 52 weeks was designed to demonstrate if a diet and physical activity group intervention in the workplace would result in changes in risk factors for antioxidant damage and therefore reduce the risk for lifestyle diseases. The effect of the addition of kiwifruit to the diet on markers of oxidative stress was also measured in a crossover sub study within this study. Fifty two healthy subjects (male 24, female 28, mean age 46), completed the 12 week study with measurements points being at 0, 3, 6, 9 and 12 weeks. Thirty eight subjects presented for another set of measurements at 52 weeks. The intervention started at week 3 and the kiwifruit crossover treatment was launched between weeks 6 and 12.Ferric reducing ability of plasma (FRAP) assay was utilized to measure the changes in plasma antioxidant activity(AOA) and thiobarbituric acid reactive substances (TBARS) assay to measure the changes in plasma malondialdehyde (MDA), as a marker of lipid peroxidation (LP) at each measurement point. Since almost all participants had a normal range of baseline measurements of plasma AOA and LP (plasma MDA), they were categorized as relatively low and high AOA (1200micromol/L cut off point) and LP groups (1.70mmol/L cut off point), as well as divided into male and female groups. The effect of changed diet and increased physical activity during the 12 week study period resulted in a significant increase (P<0.05) in plasma AOA. The changes were much higher in low AOA group (P=0.005) and in male subjects (P<0.005), while no changes were observed in subjects with already high AOA at baseline. The increased plasma AOA level was maintained and increased even more over the year. No changes were observed in LP (plasma MDA). The effect of kiwifruit on the markers of oxidative stress was modest, the 3-week daily kiwifruit consumption (2-3 kiwifruit per day) resulted in significant increase (P=0.01) in plasma AOA only in female subjects within the low AOA group. However, the precision and validity of the measurements were limited by a possible loss of vitamin C due to storage of the plasma samples rather than analysis when fresh. Given that kiwifruit is particularly high in vitamin C the effect of the addition of kiwifruit to the diet might not have been detected. In this study it was shown that a group diet and physical activity intervention within the workplace can increase the level of plasma antioxidant activity and thereby reduce the risk for oxidative stress and related lifestyle diseases.