Objective: Assessing changes in dietary intake during the transition from adolescence to adulthood is challenging given the need for age-appropriate tools at different developmental stages. The present study investigated the comparability of intake estimates as assessed with the youth/adolescent and adult forms of Willett's FFQ.
Design: Young adults were first asked to complete the adult FFQ as part of a larger study, Project EAT-III (Eating and Activity in Teens and Young Adults). A stratified random sample of respondents was invited to complete the youth/adolescent FFQ by mail within a 3-week period.
Setting: Participants were members of a longitudinal cohort who completed baseline surveys (including the adolescent FFQ) at schools in Minneapolis/St. Paul, Minnesota and completed Project EAT-III surveys online or by mail in 2008-2009.
Subjects: There were ninety-one men and 103 women (median age = 24·6 years) who completed both forms of the FFQ.
Results: The adolescent and adult forms did not provide comparable absolute intake estimates. However, with few exceptions, correlation coefficients between intake estimates were moderate (r = 0·4-0·6). Furthermore, the percentage of individuals classified into the same quartile rank category based on their responses to the adolescent and adult forms was ≥50 % for fibre, vitamins A and E, and servings of fruit (excluding juice), vegetables, dairy, whole grains and soft drinks.
Conclusions: Although responses on the adolescent and adult FFQ cannot be compared to describe changes in absolute intake over time, these tools provide comparable intake rankings and may be used together in longitudinal studies to investigate influences on diet.