Monetary cost of self-reported diet in relation to biomarker-based estimates of nutrient intake in young Japanese women

Abstract

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:

Relation of food cost to healthfulness of diet among US women

“…This condition raises the potential for correlated errors, which was recognized in earlier studies of diet and cost (45,46) and which, in our analysis, was mitigated in 2 ways: First, coefficients for calculating the AHEI score were both positive and negative (ie, certain foods increased scores, whereas others decreased them), although those for cost were all positive. As such, a correlation of errors would not necessarily exist, and if it did, it would tend to be low.…”

“…Previous studies have investigated the relation between the healthfulness of diet and its cost by linking local or national food prices to food items reported on a questionnaire (2,3,6,11,45,48), diet record (5), 24-h recall (4), or face-to-face interview (4). Previous studies have also defined a healthful diet in a variety of ways: for example, in terms of adherence to a Mediterraneanstyle diet (6,14) or HEI (6) or as reflected by intake of select macro-and micronutrients (13).…”

Are socio-economic disparities in diet quality explained by diet cost?

“…Studies from Japan34 35 and Europe36–39 have shown that higher-cost diets are higher in nutritional quality34 36 38 39 and are associated with a lower body mass index 34 36 40. Fewer studies have examined food prices and diet cost in the context of socio-economic disparities in nutrition.…”

Measuring diet cost at the individual level: a comparison of three methods

“…17, 18, 19 More typically, diet costs are estimated by linking prices to diet history or food frequency questionnaires (FFQs). Following this approach, studies conducted in Europe, 12, 14, 20 the USA 11, 21, 22 and Japan 13, 23, 24 have produced diet cost estimates based on fixed tables of food prices containing 57–384 foods. However, costs estimated from FFQs might not be directly comparable to those obtained with diet diaries.…”