Original Article

European Journal of Clinical Nutrition (2008) 62, 1038–1046; doi:10.1038/sj.ejcn.1602815; published online 30 May 2007

Relative validity of a food frequency questionnaire used in the Inter99 study

Guarantor: U Toft.

Contributors: TJ was responsible for the design and conduct of the Inter99 study. LK was responsible for the design and conduct of the validation study. AB and JJ were responsible for the biochemical analyses. UT was responsible for conducting the data analysis, interpretation of the data and writing of the manuscript. All the authors participated in editing the manuscript and provided advice regarding interpretation of the results. None of the contributing authors had any financial or personal interests in any of the bodies sponsoring this research.

U Toft1, L Kristoffersen1, S Ladelund1, A Bysted2, J Jakobsen2, C Lau3, T Jørgensen3, K Borch-Johnsen2 and L Ovesen4

  1. 1Research Centre for Prevention and Health, Glostrup University Hospital, Glostrup, Denmark
  2. 2Department of Food Chemistry, The Danish Institute for Food and Veterinary Research, Mørkhøj Bygade 19, Søborg, Denmark
  3. 3Steno Diabetes Centre, Niels Steensensvej 2, Gentofte, Denmark
  4. 4The Danish Heart Foundation, Hauser Plads 10, Copenhagen, Denmark

Correspondence: U Toft, Research Centre for Prevention and Health, Glostrup University Hospital Building 84/85, DK-2600 Glostrup, Denmark. E-mail: ulto@glostruphosp.kbhamt.dk

Received 3 January 2007; Revised 12 April 2007; Accepted 13 April 2007; Published online 30 May 2007.

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Abstract

Objective:

 

To evaluate the validity of the Inter99 food frequency questionnaire (FFQ) compared with a 28-days' diet history and biomarkers.

Subjects:

 

A random sample of 13 016 individuals were drawn from a general population and invited for a health screening programme. Participation rate was 52.5%. All high-risk individuals were re-invited for assessment after 1 and 3 years and completed a 198-item FFQ at all three occasions. Participants attending for 3 years follow-up were invited to participate in the validation study, including a 28-days' diet history, a 24-h urine collection and a fasting blood sample. Overall, 264 subjects participated.

Results:

 

Spearman's rank correlation coefficients between the two dietary methods ranged from 0.31(beta-carotene) to 0.64 (fruits) in men and from 0.31 (polyunsaturated fat and sodium) to 0.64 (fruits) for women. The proportion of individuals classified in the same or adjacent quintiles were, on average, 72% for men and 69% for women. Gross misclassification was found on average in 2%. The correlation coefficients of the residuals ranged from 0.27 (sodium) to 0.61 (fruits) for men and from 0.21 (sodium) to 0.62 (B12-vitamin) for women. Correlation coefficients between fruit and vegetable intake and carotenoids ranged from -0.08 (lycopene) to 0.44 (alpha-carotene). For the residuals the correlation coefficients ranged from -0.004 (lycopene) to 0.47 (alpha-carotene).

Conclusion:

 

The Inter99 FFQ and the residuals of the intake provide acceptable classification of individuals according to their dietary intakes and the FFQ gives a good quantitative measurement of key dietary components.

Keywords:

validation, food frequency questionnaire, diet history, carotenoids, nitrogen

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