Abstract

Food frequency questionnaire is a cost effective alternative for measuring dietary intake when conducting large scale surveys. We investigated the validity of a 171-item semi-quantitative food frequency questionnaire in assessing food and nutrient intakes and the prescribed intervention measure during a randomized field trial. Eighty-seven free-living adults (48 females and 39 males) aged 30-72 years provided dietary information by self-administering the Walnut Study Dietary Assessment Questionnaire (WSDAQ), which assessed intake over the past six months, and through seven unannounced non-consecutive 24-hour dietary recalls by telephone. Participants were randomly assigned to either a walnut or habitual diet at baseline. For six months, the habitual diet group ate their usual diet while the walnut diet group incorporated moderate amounts of walnuts (~12% of energy) into their usual diet. We determined the validity of the WSDAQ against 24-hour dietary recalls through measures of central tendency and correlation analyses with correction for attenuation. The prescribed intervention measure was walnut intake ≥ 1 serving/day or ALA intake ≥ 1.1% of energy for the walnut diet group and non-intake of walnuts or α-linolenic acid (ALA) intake < 1.1% of energy for the habitual diet group. Twenty-nine out of 33 nutrients as well as vegetables, fruits, and desserts were overestimated while sugar/sweets and dairy/egg were underestimated by the WSDAQ Correction for attenuation resulted to increased validity for grains (r=0.79), vegetables (r=0.77), fruits (r=0.80), meats (r=0.67), dairy/eggs (r=0.36), walnuts (r=0.82), water (r=0.63), and sugar/sweets (r=0.44), but did not correct correlations for alcoholic beverages (r=0.85), other nuts (r=0.34), fats & oils (r=0.40), non-alcoholic beverages (r=0.68) and desserts (r=0.18) due to high within-person variation. Crude correlations for nutrients ranged from 0.08 (total vitamin E) to 0.84 (alcohol); energy-adjustment increased these correlations. Correction for attenuation increased the correlations for nutrients, which ranged from 0.33 (total protein) to 0.96 (vitamin C), but high within person variation did not allow correction for 13 of the 33 nutrients. Validity correlations for the markers, walnuts and ALA, were high whether attenuated or deattenuated, but mean intakes were significantly different between the two methods for both diet groups. The Walnut Study Dietary Assessment Questionnaire is a reasonably valid tool in assessing food and nutrient intakes and the prescribed intervention measure in the context of a dietary intervention trial. Results suggest overestimation of socially-desirable foods and underestimation of less socially-desirable foods on this questionnaire. The questionnaire also overestimated nutrient intakes by 1-88%. Steps need to be taken to increase the accuracy of this food frequency questionnaire in estimating absolute intakes.

Department

Nutrition

School

School of Public Health

First Advisor

Joan Sabaté

Second Advisor

Pramil N. Singh

Third Advisor

Ella Haddad

Degree Name

Doctor of Public Health (DrPH)

Degree Level

Ph.D.

Year Degree Awarded

2004

Date (Title Page)

6-2004

Language

English

Library of Congress/MESH Subject Headings

Nutrition; Diet

Type

Dissertation

Page Count

xvi; 261

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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