Number of days required for assessing usual nutrient and antioxidant intakes in a sample from a U.S. healthy college population.

OBJECTIVE

The primary aim of this study was to determine the number of days required to assess usual antioxidant intake with a defined level of accuracy in a sample of healthy college students. The secondary aim of this study was to increase the validity of the calculation of days by first determining the prevalence of misreporting energy intake in 30-d food records (FRs).

METHOD

We examined the percentage of misreporting, the within- and between-person variations of nutrient intake, and the minimum days required to estimate a person's true intake with a correlation coefficient r ≥ 0.9. Sixty students from the University of Connecticut completed a 30-d FR, which was analyzed using the Nutrition Data System for Research software combined with Flavonoid and Proanthocyanidin Provisional Table.

RESULTS

Twenty-seven percent (44 average reporters) included in the dietary analysis misreported after applying the Goldberg cutoff equation. The within-person variation was greater than the between-person variation with the variance ratios ranging from 1.10 to 10.51. After adjusting for energy and sex, a 7-d FR was adequate to achieve r ≥ 0.9 for fat, carbohydrate, protein, lycopene, and proanthocyanidin, whereas α-tocopherol, total carotenoids, and flavonoids required 8 d. The remaining antioxidants required between 10 and 45 d.

CONCLUSIONS

Overall, micronutrients and antioxidants had a greater daily variation than macronutrients and the majority required more than 7 d to assess usual intakes for this population.