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Open Access Research article

Development and validation of a food-based diet quality index for New Zealand adolescents

Jyh Eiin Wong12*, Winsome R Parnell1, Anna S Howe1, Katherine E Black1 and Paula ML Skidmore1

Author Affiliations

1 Department of Human Nutrition, University of Otago, Dunedin 9054, New Zealand

2 Nutritional Sciences Programme, School of Healthcare Sciences, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Kuala Lumpur 50300, Malaysia

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BMC Public Health 2013, 13:562  doi:10.1186/1471-2458-13-562

Published: 8 June 2013

Abstract

Background

As there is no population-specific, simple food-based diet index suitable for examination of diet quality in New Zealand (NZ) adolescents, there is a need to develop such a tool. Therefore, this study aimed to develop an adolescent-specific diet quality index based on dietary information sourced from a Food Questionnaire (FQ) and examine its validity relative to a four-day estimated food record (4DFR) obtained from a group of adolescents aged 14 to 18 years.

Methods

A diet quality index for NZ adolescents (NZDQI-A) was developed based on ‘Adequacy’ and ‘Variety’ of five food groups reflecting the New Zealand Food and Nutrition Guidelines for Healthy Adolescents. The NZDQI-A was scored from zero to 100, with a higher score reflecting a better diet quality. Forty-one adolescents (16 males, 25 females, aged 14–18 years) each completed the FQ and a 4DFR. The test-retest reliability of the FQ-derived NZDQI-A scores over a two-week period and the relative validity of the scores compared to the 4DFR were estimated using Pearson’s correlations. Construct validity was examined by comparing NZDQI-A scores against nutrient intakes obtained from the 4DFR.

Results

The NZDQI-A derived from the FQ showed good reliability (r = 0.65) and reasonable agreement with 4DFR in ranking participants by scores (r = 0.39). More than half of the participants were classified into the same thirds of scores while 10% were misclassified into the opposite thirds by the two methods. Higher NZDQI-A scores were also associated with lower total fat and saturated fat intakes and higher iron intakes.

Conclusions

Higher NZDQI-A scores were associated with more desirable fat and iron intakes. The scores derived from either FQ or 4DFR were comparable and reproducible when repeated within two weeks. The NZDQI-A is relatively valid and reliable in ranking diet quality in adolescents at a group level even in a small sample size. Further studies are required to test the predictive validity of this food-based diet index in larger samples.

Keywords:
Diet quality index; Dietary patterns; Validity; Adolescents; New Zealand