Objective The aim of this study was to develop a questionnaire for use by nutrition professionals to enable evaluation of popular diet books.
Design A questionnaire was developed incorporating quantified criteria based on current authoritative nutrition guidelines. Twenty two questions were included, relating to nutritional adequacy, daily energy allowance, recommended rate of weight loss, flexibility and sustainability, physical activity advice, use of supplements, claims, author’s credentials, and scientific evidence. The questionnaire was used to rate 35 diets in 20 popular diet books sold in Australia in 2001, in order to test its practicality, validity and sensitivity. A computerised dietary analysis of three days of menus from each book was used to assess the validity of the questions assessing nutritional adequacy.
Main outcome measures Assessment scores of each book and correlation with dietary analyses.
Statistical analysis Spearman rank correlation was used to compare the nutritional adequacy of the diets assessed by the dietary assessment scores from the questionnaire and the numbers of nutrients likely to be provided at <70% RDI or <100% RDI. One way ANOVA was used to compare the mean scores of books written by those with nutrition qualifications, medical qualifications, and others.
Results The scoring of the questionnaire was found to correlate well with the computerised analysis of the diets. Overall scores for the 20 books tested ranged from 32 to 97 out of a possible 100. Only five of the books were found by the assessment criteria to have diets compatible with current dietary and public health guidelines, with scores of over 80. Three diets provided less than 4200 kJ per day, whilst five books advertised weight loss results of greater than 1kg per week and promoted or used ‘fast’ weight loss as a selling point. The majority of books relied on testimonials rather than supporting their results with data published in peer reviewed journals. Books authored by people with nutrition qualifications rated highest.
Conclusion The questionnaire provides a useful standardised method of ranking the nutritional adequacy of popular diets books and evaluating their approach to weight loss, suitable for use by nutrition professionals.