title: Relative validity of a food frequency questionnaire used to assess food intake during a dietary intervention study.
abstract: To develop a cost-effective alternative for evaluating dietary intake in large-scale intervention trials of cancer and cardiovascular disease outcomes, we designed and validated a semiquantitative food frequency questionnaire (FFQ). We collected 6 to 8 of the 24-hr dietary recalls from 87 adults (ages 30-72 yr) who were randomly assigned to a walnut-supplemented diet or a control diet in a 6-mo dietary intervention trial. Relative validity of a 171-item FFQ in assessing intake of selected foods and the prescribed intervention (intake > or =25 g/day or intake < 2 g of walnuts) was determined using 24-h dietary recalls as the reference. De-attenuated correlations between FFQ and dietary recalls were .82 for walnuts, .80 for fruits, .79 for grains, .77 for vegetables, .63 for water, .44 for sweets, and .36 for dairy/eggs. High within-person variation did not allow de-attenuation for the remaining foods, but uncorrected correlations were high (> .7) for the beverage variables. The FFQ correctly classified 86 out of 87 subjects in the 2 prescribed intervention groups. The FFQ can provide an accurate measure of a food-based intervention (i.e., walnut supplementation) in a trial setting and can also accurately estimate a number of other food groups consumed during the trial.
authors.affiliation: Department of Nutrition, School of Public Health, Loma Linda University, Loma Linda, CA 92350, USA.
authors.forename: Gina
authors.initials: G
authors.lastname: Segovia-Siapco
authors.forename: Pramil
authors.initials: P
authors.lastname: Singh
authors.forename: Ella
authors.initials: E
authors.lastname: Haddad
authors.forename: Joan
authors.initials: J
authors.lastname: Sabate
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D002140:California; D004032:Diet / Q000706:statistics & numerical data*; D015930:Diet Records; D004034:Diet Surveys; D004435:Eating / Q000502:physiology*; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D031324:Juglans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*