One-day versus usual intake

Two food consumption concepts must be distinguished:  one-day intake and usual intake.  One-day intake is total nutrient intake over a specific 24-hour period.  These data were collected by the 2004 Canadian Community Health Survey — Nutrition during an interview in which respondents were asked to describe everything they ate from midnight to midnight the previous day.  Usual intake is an overview of food typically consumed in a day, and it cannot be directly estimated based on one-day intake.  However, estimates of the proportion of the population below or above a given threshold require a usual intake distribution.

Usual intake varies from one individual to another.  One-day intake varies not only from one individual to another, but also from day to day for a given individual.  To estimate usual intake, day-to-day variation for individuals was removed using Software for Intake Distribution Estimation (SIDE).³  With a series of mathematical transformations, this software is able to estimate each component of the variance and to estimate the distribution of usual intake of a nutrient.^4,13  For these calculations, day of the week was used to partially account for the effect of classification.