Objective: We aimed to assess the day-to-day variation in twelve one-day diet records over one year from 131 residents of urban and rural areas in the western region of Japan. Methods: Between 2014 and 2015, the participants provided repeated one-day diet records once a month. We estimated the intraclass correlation coefficient (ICCs) for intakes for energy and 39 crude and energy-adjusted nutrients using linear mixed models. Results: Among the unadjusted nutrients, ICCs ranged from 0.05 (95 percent confidence interval = 0.03–0.09) for vitamin A retinol equivalent (RE) to 0.55 (95% CI = 0.48–0.62) for potassium. After energy adjustment, the ICCs were 0.02 (95 percent confidence interval = 0.03–0.09) for vitamin A (RE) and 0.52 (95 percent confidence interval = 0.45–0.59) for potassium. Intakes of energy-adjusted macronutrients tended to have moderate degrees of day-to-day coefficients of variation (CVw,
range = 0.13–0.23, mean = 0.18), while the coefficients of variation for intakes of micronutrients varied dramatically (CVw,
range = 0.17–2.59, mean = 0.54). Conclusion: There were large day-to-day variations in nutrient intake assessed by diet records among urban and rural residents in the western region of Japan. This study provided information on the reproducibility of crude and energy-adjusted nutrients that may be useful for other dietary studies in Japanese populations.
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