Variations in antioxidant intake and determination of number of days required for assessing usual intake of antioxidants in diet

Consumption of antioxidant rich foods is important at every age for decreasing risks of chronic disease; however, limited data exists on within‐ and between‐person variation of daily antioxidant intake from diet. This study aimed: 1) to validate 30 consecutive diet recalls by identifying subjects who misreported intakes 2) to describe the variation and distribution of antioxidants compared to macronutrients and 3) to calculate the number of days required to estimate usual nutrient intake with a defined level of accuracy in healthy young adults. We utilized the USDA Flavonoid and Proanthocyanidin databases and food consumption data of 60 students at the University of Connecticut. We found 27% misreported after applying the Goldberg cut‐off equation defined for our population. Increasing the number of days had a greater effect on decreasing the between person variation for antioxidants when comparing the mean distributions from 1, 7, and 30 days of intake. After adjusting for energy and gender, a 7‐day dietary recall was adequate to achieve r ≥ 0.9 for fat, carbohydrate, protein, lycopene, and proanthocyanidin while α‐tocopherol, total carotenoids, and flavonoids required 8 days. The remaining antioxidants required less than 30 days (except β‐cryptoxanthin). Overall, antioxidants had a greater daily variation than macronutrients and 7 days or more is adequate to estimate usual intake for this target population.