Objective: All previous studies on monetary diet cost have examined the relationship of monetary cost of self-reported diet to self-reported, rather than biomarker-based, estimates of dietary intake. The present cross-sectional study examined the association between monetary costs of self-reported diet and biomarker-based estimates of nutrient intake. Design: Monetary diet cost (Japanese yen/1000 kJ) was calculated based on dietary intake information from a self-administered, comprehensive diet history questionnaire using retail food prices. Biomarker-based estimates of nutrient intake (percentage of energy for protein and mg/1000 kJ for K and Na) were estimated based on 24 h urinary excretion and estimated energy expenditure. Setting: A total of fifteen universities and colleges in Japan. Subjects: A total of 1046 female Japanese dietetic students aged 18-22 years. Results: Total monetary diet cost showed a significant positive association with biomarker-based estimates of protein, K and Na. Vegetables and fish were not only the main contributors to total monetary diet cost (16?4 % and 15?5 %, respectively) but also were relatively strongly correlated with total monetary diet cost (Pearson's correlation coefficient: 0?70 and 0?68, respectively). Monetary cost of vegetables was significantly positively associated with all three nutrients, while that of fish showed a significant and positive association only with protein.Conclusions: Total monetary cost of self-reported diet was positively associated with biomarker-based estimates of protein, K and Na intake in young Japanese women, and appeared mainly to be explained by the monetary costs of vegetables and fish.
Keywords
Monetary diet cost 24 h urine EpidemiologyWhile food choice is influenced by a large number of factors (1) , the price of food is clearly an important determinant (2,3) . Generally, energy-dense and nutrientdilute foods such as cereals, fats and oils, and sugar and sweets provide dietary energy at lowest cost. Conversely, the cost per kilojoule of energy-dilute and nutrient-dense foods, including vegetables, fish and fruit, is much higher. If healthier foods cost more then so too will healthier diets. In fact, several (4)(5)(6)(7)(8)(9) although not all (10) observational studies have shown that healthful diets are more expensive than less healthful diets.However, all of these previous studies have estimated both monetary diet costs and dietary intake based on selfreported dietary intake obtained by the same dietary assessment method, resulting in an inevitable overestimation of the association between monetary diet cost and dietary intake due to errors shared by monetary diet costs and dietary intake. Given the difficulty in estimating y The members of the Japan Dietetic Students' Study for Nutrition and Biomarkers Group (in addition to the authors) are as follows: