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Environ Health Insights. 2009; 3: 27–35.
Published online 2009 May 12.
PMCID: PMC2872571

Monetary Diet Cost is Associated with not only Favorable but also Unfavorable Aspects of Diet in Pregnant Japanese Women: The Osaka Maternal and Child Health Study

Kentaro Murakami,1 Yoshihiro Miyake,2 Satoshi Sasaki,1 Keiko Tanaka,2 Yukihiro Ohya,3 Yoshio Hirota,4 and Osaka Maternal and Child Health Study Group5

Abstract

While several observational studies in European countries have shown that higher monetary diet cost is associated with healthier diets, information on the relationship of cost to diet quality in other countries is sparse, including Japan. This cross-sectional study examined the association between monetary diet cost and dietary intake in a group of pregnant Japanese women. Subjects were 596 pregnant Japanese housewives. Dietary intake was estimated using a validated, self-administered, comprehensive diet history questionnaire. Monetary diet cost was calculated using retail food prices. Values of monetary diet cost and nutrient and food intake were energy-adjusted using the density method. Monetary diet cost was associated positively with the intake of protein, total fat, saturated fatty acids, dietary fiber, cholesterol, sodium, potassium, calcium, magnesium, iron, vitamins A, D, E, C, and folate, and inversely with that of carbohydrate. For foods, cost was associated positively with the intake of potatoes, pulses and nuts, fish and shellfish, meat, dairy products, vegetables, and fruits, and inversely with that of rice and bread. No association was seen for noodles, confectioneries and sugars, fats and oils, or eggs. Cost was also associated inversely with dietary energy density. In conclusion, monetary diet cost was associated with not only favorable aspects of diet, including a higher intake of dietary fiber, key vitamins and minerals, fruits, and vegetables and lower dietary energy density, but also unfavorable aspects, including a higher intake of fat and sodium and lower intake of carbohydrate and rice, in a group of pregnant Japanese women.

Keywords: diet cost, nutrient intake, food intake, pregnant women, Japan

Introduction

While food choice is influenced by a large number of factors,1 the price of food is an important determinant.2,3 Generally, energy-dense and nutrient-dilute foods such as cereals, fats and oils, and sugar and confectioneries provide dietary energy at lowest cost.49 Conversely, the cost per calorie of energy-dilute and nutrient-dense foods, including fish and shellfish, vegetables, and fruits is much higher.49 If healthier foods cost more then so too will healthier diets, and several observational studies conducted in European countries have in fact shown that healthful diets are more expensive than less healthful diets,49 albeit that the currently available procedure for estimating monetary diet cost is based on the assumption that all foods are purchased and then prepared and consumed at home, and hence cannot consider the monetary cost of eating out.10 Given the important role of nutrition in promoting health,11,12 the positive association between monetary diet cost and diet quality may explain, at least in part, the socioeconomic gradient in health widely observed in Western countries, with higher socioeconomic position associated with better health.1315

However, information on the relationship of monetary diet cost to diet quality in other countries is sparse, including Japan. Considering the unclear or even inverse association between socioeconomic position and health status observed in several Japanese populations,1618 the association between monetary diet cost and diet quality may differ between European countries and Japan. In a study of Japanese female dietetic students, for example, monetary diet cost was not necessarily associated with healthier dietary intake patterns.19 This finding may have been confounded by a lack of information on whether the participants bought their food themselves, however, given that the majority (89%) lived with their family.19 Because the relationship between monetary diet cost and diet quality is an important public health issue, further investigation in Japanese people is clearly needed. Additionally, the association between monetary diet cost and dietary intake has not been investigated among women during pregnancy, a nutritionally important lifestyle stage, even in Western countries.

The present cross-sectional study examined the association between monetary diet cost and dietary intake in a group of pregnant Japanese women using baseline data from the Osaka Maternal and Child Health Study (OMCHS). We selected only housewives who did not habitually eat out and who lived in nuclear families in non-agricultural societies for accurate estimation of monetary diet cost. We hypothesized that monetary diet cost is associated with both favorable and unfavorable aspects of diet.

Methods

Subjects

The subjects in the present analysis were participants in the baseline survey of the OMCHS, an ongoing prospective cohort study, the main purpose of which was to investigate preventive and risk factors for maternal and child health problems. Details of the OMCHS have been published elsewhere.20,21 Briefly, all pregnant women in Neyagawa City, Osaka Prefecture (metropolis in Japan with a total population of approximately 8.8 million), were recruited between November 2001 and March 2003. Of 3639 eligible women, 627 (17.2%) took part in the study. An additional 375 pregnant women living in other neighborhood areas were enrolled in the study between December 2001 and November 2003, giving a total of 1002 pregnant women completing the baseline survey. Written informed consent was obtained from each woman. The protocol of the OMCHS was approved by the ethics committees of Osaka City University School of Medicine, Japan.

For the present analysis, we excluded women living in an expanded family (n = 127), those working outside the home (n = 288), and those who dined out 16 times or more during the preceding month (i.e. four times or more per week) (n = 118). Because some women fell into more than one exclusion category, the final analysis sample comprised 596 women.

Measurements

Baseline assessment of the OMCHS included a set of two self-administered questionnaires. The participants mailed the answered questionnaires to the data management center. Research technicians completed missing or illogical data by telephone interview.

One of the self-administered questionnaires was a validated, self-administered, comprehensive diet history questionnaire (DHQ) that assesses dietary habits during the preceding month. Details of the DHQ’s structure, calculation of dietary intake, and validity for commonly studied nutritional factors have been published elsewhere.2225 Briefly, the DHQ is a 16-page structured questionnaire which asks about the consumption frequency and portion size of selected foods commonly consumed in Japan as well as general dietary behavior and usual cooking methods.22 Estimates of daily intake for foods (150 items in total), nutrients, and energy were calculated using an ad hoc computer algorithm for the DHQ,22,25 based on the Standard Tables of Food Composition in Japan.26

Monetary diet cost (Japanese yen/day) was calculated by multiplying the amount of each food estimated from the DHQ (g/day) by the estimated price of the food (Japanese yen/g) and summing the products (1 Japanese yen = 0.0077 pound sterling = 0.0085 euros = 0.0110 US dollars in February 2009). Detailed descriptions of the cost calculation method as well as the monetary cost of each food have been published elsewhere.19,27 Briefly, the price of each food was determined based on the National Retail Price Survey 2004.28 For foods whose prices were not published in the survey (13 items), prices were taken from the websites of a nationally distributed supermarket (Seiyu, Tokyo, Japan) or fast-food restaurant (McDonalds, Tokyo, Japan and Mister Donut, Tokyo, Japan) chains. Alcoholic beverages (six items), non-caloric beverages (four items), and water (three items) were excluded from calculation.9 Costs of combined foods such as pizza were calculated using the prices of frozen equivalents.8 Costs were estimated based on the assumption that all foods were purchased and then prepared and consumed at home.10

To minimize the influence of dietary misreporting, an ongoing controversy in studies that collect dietary information using self-report instruments,29 values of monetary diet cost as well as intakes of nutrients and foods were energy-adjusted using the density method (i.e. monetary diet cost per 1000 kcal of energy, percentage of energy for energy-providing nutrients, and amount per 1000 kcal of energy for other nutrients and foods). Dietary energy density (kcal/g) was calculated based on foods only (128 items, excluding 22 beverages), as described elsewhere.30 In a previous study of 92 Japanese women, Pearson correlation coefficient between the DHQ and 16-day weighed dietary records were 0.57 for monetary diet cost, suggesting satisfactory validity of the DHQ in terms of monetary diet cost.27

The other self-administered questionnaire elicited information on potential confounding factors, including age (28 years or less, 29–31 years, and 32 years or more), gestational age (14 weeks or less, 15–20 weeks, and 21 weeks or more), parity (nulliparous and multiparous), cigarette smoking (never, former, and current), changes in diet in the previous one month (none or few, slight, and substantial), physical activity (low; and medium or high), partner’s education [low (12 years or less), medium (13–14 years), and high (15 years or more)], education [low (12 years or less), medium (13–14 years), and high (15 years or more)], and household income as calculated considering differences in household size and composition31 [divided into approximate tertiles: low (2,499,999 yen/year or less), medium (2,500,000–3,099,999 yen/year), and high (3,100,000 yen/year or more)].

Statistical analysis

All statistical analyses were performed using SAS statistical software version 9.1 (SAS Institute Inc., Cary, NC, USA). Using the PROC GLM procedure, linear regression models were constructed to examine the association of monetary diet cost with dietary intake of selected nutrients and foods. For analyses, subjects were categorized into quartiles according to monetary diet cost. Mean (and standard error) values of nutrient and food intake were calculated by quartile of monetary diet cost with adjustment for potential confounding factors, including age, gestational age, parity, cigarette smoking, changes in diet in the previous month, physical activity, partner’s education, education, and household income. Tests for trends were performed by modeling the median value of each quartile category as a continuous variable. All reported P-values are two-tailed, and a P-value of <0.05 was considered statistically significant.

Results

Dietary characteristics of the 596 women are shown in Table 1. Mean monetary diet cost was 458.9 Japanese yen/1000 kcal, while mean percentages of intake of protein, total fat, and carbohydrate were 13.4%, 30.0%, and 55.6% of energy, respectively. Selected characteristics by quartile of monetary diet cost are shown in Table 2. Women in the higher quartiles of cost tended to be never smokers and have changes in diet in the previous month, a partner with higher education, higher education, and higher household income.

Table 1.
Dietary characteristics of the subjects (n = 596).a
Table 2.
Selected characteristics according to quartile category of monetary diet cost (n = 596).a

Dietary characteristics by quartile of monetary diet cost are shown in Table 3. At the nutrient level, monetary diet cost was associated positively with the intake of protein, total fat, saturated fatty acids, dietary fiber, cholesterol, sodium, potassium, calcium, magnesium, iron, vitamins A, D, E, and C, and folate, and inversely with that of carbohydrate. At the food level, monetary diet cost was associated positively with the intake of potatoes, pulses and nuts, fish and shellfish, meat, dairy products, vegetables, and fruits, and inversely with that of rice and bread. No association was seen for noodles, confectioneries and sugars, fats and oils, or eggs. Further, monetary diet cost was inversely associated with dietary energy density.

Table 3.
Dietary characteristics according to quartile category of monetary diet cost (n = 596).a

Discussion

Consistent with a previous study of Japanese female dietetic students,19 we found that monetary diet cost was associated with not only favorable aspects of diet such as a higher intake of dietary fiber, key vitamins and minerals, and fruits and vegetables and lower dietary energy density, but also unfavorable aspects of diet such as a higher intake of fat and sodium and lower intake of carbohydrate and rice in a group of pregnant Japanese women. These findings somewhat conflict with those of previous Western studies, in which monetary diet cost has been consistently associated with healthier diets, including higher intake of key micronutrients, fruits, and vegetables, lower intake of fats and sweets, and lower dietary energy density.49

For Japanese people, rice is a staple food which is consumed at almost every meal, accompanied by a main and several side dishes consisting mainly of fish and shellfish, meat, egg, vegetables, and pulses. Rice is relatively inexpensive compared with the component foods of such main and side dishes in Japan.19 We previously speculated that persons with a limited budget for foods would mainly consume rice, with a relatively restricted amount or variety of main and side dishes, while those with a larger food budget would have an increased amount or variety of main and side dishes and decreased consumption of rice.19 This hypothesis may be supported by the decreasing consumption of rice and increasing consumption of other foods such as meat, vegetables, fish and shellfish, and pulses32 seen with the increase in the Gross National Product of Japan33 from 1955 to 2000.19

With regard to the unfavorable aspects of diet at the nutrient level, the higher intake of total fat, saturated fatty acids, and cholesterol and lower intake of carbohydrate seen with increasing monetary diet cost appeared to be due to lower rice consumption (and dietary intake patterns associated with lower rice intake) with increasing monetary diet cost; in apparent support of this, rice intake was in fact negatively associated with the intake of total fat (Pearson correlation coefficient: −0.52), saturated fatty acids (−0.48), and cholesterol (−0.19) and positively with carbohydrate intake (0.44). The higher intake of sodium seen with increasing monetary diet cost may be due to higher intake of vegetables, meat, fish and shellfish, and pulses and nuts, because in Japan these foods are usually accompanied by seasonings with a salty taste, such as salt, soy sauce, miso (fermented soybean paste), and dressings. Intake of these foods was in fact positively associated with sodium intake in the present study (Pearson correlation coefficients: 0.33, 0.12, 0.30, and 0.35, respectively).

Several limitations of the study warrant mention. First, the study subjects were selected pregnant Japanese housewives. Additionally, response rate for the 627 women living in Neyagawa City was only 17.2%, and could not be calculated for the remaining 375 women living in other areas because the exact number of eligible subjects among the sources from which they recruited was not available. Thus, the present results could not be extrapolated to other populations.

Although the validity of the DHQ appears reasonable with regard to commonly studied nutritional factors,2225 it was not specifically designed to measure monetary diet cost. This limitation is common to other studies on this topic.49,19 Additionally, food prices were derived from the National Retail Price Survey and websites of nationally distributed supermarket and fast food restaurant chains. As this procedure gives only an approximation of actual diet costs, the results of the present study should be interpreted with caution, although a similar methodology has been used in all previous observational studies.49,19 Nevertheless, the satisfactory validity of this DHQ regarding monetary diet cost against 16-day weighed dietary records as described above may provide some reassurance.27

In conclusion, monetary diet cost was associated with not only favorable but unfavorable aspects of diet in a group of pregnant Japanese women. Because the relation between monetary diet cost and diet quality is an important public health topic, further research is needed to investigate whether the association found in this specific group of subjects would also be observed in other Japanese populations.

Acknowledgments

We thank the Neyagawa City Government, Hirakata City Government, Katano City Government, Shijonawate City Government, Kaizuka City Government, Takaishi City Government, Hannan City Government, Neyagawa City Medical Association, Hirakata City Medical Association, and Kadoma City Medical Association for their valuable support; and Tomoko Shibazaki, Nahoko Nishimura, and Naomi Takaoka for their assistance.

Other members of the Osaka Maternal and Child Health Study Group are as follows: Shoichi Miyamoto (Department of Public Health, Osaka City University Graduate School of Medicine); Ichiro Matsunaga, Toshiaki Yoshida, and Hajime Oda (Osaka Prefectural Institute of Public Health); Hideharu Kanzaki and Mitsuyoshi Kitada (Department of Obstetrics and Gynecology, Kansai Medical University); Yorihiko Horikoshi (Department of Obstetrics and Gynecology, Kansai Medical University Kori); Osamu Ishiko, Yuichiro Nakai, Junko Nishio, and Seiichi Yamamasu (Department of Obstetrics and Gynecology, Osaka City University Graduate School of Medicine); Jinsuke Yasuda (Department of Obstetrics and Gynecology, Matsushita Memorial Hospital); Seigo Kawai (Department of Obstetrics and Gynecology, Hoshigaoka Koseinenkin Hospital); Kazumi Yanagihara (Yanagihara Clinic); Koji Wakuda (Department of Obstetrics and Gynecology, Jujimoto Hospital); Tokio Kawashima (Kyoritsu Women’s Clinic); Katsuhiko Narimoto (Ishida Hospital Obstetrics, Gynecology); Yoshihiko Iwasa (Iwasa Women’s Clinic); Katsuhiko Orino (Orino Lady’s Clinic); Itsuo Tsunetoh (Tsunetoh Obstetrics and Gynecology); Junichi Yoshida (Yoshida Clinic); Junichi Iito, (Iito Obstetrics and Gynecology Clinic); Takuzi Kaneko (Kaneko Sanfujinka); Takao Kamiya (Kamiya Ladies Clinic); Hiroyuki Kuribayashi (Kuribayashi Clinic); Takeshi Taniguchi (Taniguchi Hospital); Hideo Takemura (Kosaka Women’s Hospital); and Yasuhiko Morimoto (Aizenbashi Hospital).

Footnotes

Sources of Support

This study was supported by a Grant-in-Aid (13770206, 16790351) for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology and Health and Labour Sciences Research Grants, Research on Allergic Disease and Immunology from the Ministry of Health, Labour, and Welfare.

Disclosure

The authors report no conflicts of interest.

References

1. Shepherd R. Resistance to changes in diet. Proc Nutr Soc. 2002;61:267–72. [PubMed]
2. Lennernas M, Fjellstrom C, Becker W, Giachetti I, Schmitt A, Remaut de Winter A, et al. Influences on food choice perceived to be important by nationally-representative samples of adults in the European Union. Eur J Clin Nutr. 1997;51:S8–15. [PubMed]
3. Glanz K, Basil M, Maibach E, Goldberg J, Snyder D. Why Americans eat what they do: taste, nutrition, cost, convenience, and weight control concerns as influences on food consumption. J Am Diet Assoc. 1998;98:1118–26. [PubMed]
4. Cade J, Upmeier H, Calvert C, Greenwood D. Costs of a healthy diet: analysis from the UK Women’s Cohort Study. Public Health Nutr. 1999;2:505–12. [PubMed]
5. Drewnowski A, Darmon N, Briend A. Replacing fats and sweets with vegetables and fruits—a question of cost. Am J Public Health. 2004;94:1555–9. [PubMed]
6. Drewnowski A, Monsivais P, Maillot M, Darmon N. Low-energy-density diets are associated with higher diet quality and higher diet costs in French adults. J Am Diet Assoc. 2007;107:1028–32. [PubMed]
7. Andrieu E, Darmon N, Drewnowski A. Low-cost diets: more energy, fewer nutrients. Eur J Clin Nutr. 2006;60:434–6. [PubMed]
8. Schroder H, Marrugat J, Covas MI. High monetary costs of dietary patterns associated with lower body mass index: a population-based study. Int J Obes. 2006;30:1574–9. [PubMed]
9. Maillot M, Darmon N, Vieux F, Drewnowski A. Low energy density and high nutritional quality are each associated with higher diet costs in French adults. Am J Clin Nutr. 2007;86:690–6. [PubMed]
10. Drewnowski A, Darmon N. The economics of obesity: dietary energy density and energy cost. Am J Clin Nutr. 2005;82:265S–73S. [PubMed]
11. Smith GD, Brunner E. Socio-economic differentials in health: the role of nutrition. Proc Nutr Soc. 1997;56:75–90. [PubMed]
12. Darmon N, Drewnowski A. Does social class predict diet quality? Am J Clin Nutr. 2008;87:1107–17. [PubMed]
13. Winkleby MA, Jatulis DE, Frank E, Fortmann SP. Socioeconomic status and health: how education, income, and occupation contribute to risk factors for cardiovascular disease. Am J Public Health. 1992;82:816–20. [PubMed]
14. Lantz PM, House JS, Lepkowski JM, Williams DR, Mero RP, Chen J. Socioeconomic factors, health behaviors, and mortality: results from a nationally representative prospective study of U.S. adults. JAMA. 1998;279:1703–8. [PubMed]
15. Lahelma E, Martikainen P, Laaksonen M, Aittomaaki A. Pathways between socioeconomic determinants of health. J Epidemiol Community Health. 2004;58:327–32. [PMC free article] [PubMed]
16. Martikainen P, Ishizaki M, Marmot MG, Nakagawa H, Kagamimori S. Socioeconomic differences in behavioural and biological risk factors: a comparison of a Japanese and an English cohort of employed men. Int J Epidemiol. 2001;30:833–8. [PubMed]
17. Nishi N, Makino K, Fukuda H, Tatara K. Effects of socioeconomic indicators on coronary risk factors, self-rated health and psychological well-being among urban Japanese civil servants. Soc Sci Med. 2004;58:1159–70. [PubMed]
18. Hirokawa K, Tsutusmi A, Kayaba K. Impacts of educational level and employment status on mortality for Japanese women and men: the Jichi Medical School cohort study. Eur J Epidemiol. 2006;21:641–51. [PubMed]
19. Murakami K, Sasaki S, Okubo H, Takahashi Y, Hosoi Y, Itabashi M. Monetary costs of dietary energy reported by young Japanese women: association with food and nutrient intake and body mass index. Public Health Nutr. 2007;10:1430–9. [PubMed]
20. Miyake Y, Miyamoto S, Ohya Y, Sasaki S, Matsunaga I, Yoshida T, et al. Relationship between active and passive smoking and total serum IgE levels in Japanese women: baseline data from the Osaka Maternal and Child Health Study. Int Arch Allergy Immunol. 2004;135:221–8. [PubMed]
21. Miyake Y, Sasaki S, Ohya Y, Miyamoto S, Matsunaga I, Yoshida T, et al. Soy, isoflavones, and prevalence of allergic rhinitis in Japanese women: the Osaka Maternal and Child Health Study. J Allergy Clin Immunol. 2005;115:1176–83. [PubMed]
22. Sasaki S, Yanagibori R, Amano K. Self-administered diet history questionnaire developed for health education: a relative validation of the test-version by comparison with 3-day diet record in women. J Epidemiol. 1998;8:203–15. [PubMed]
23. Sasaki S, Yanagibori R, Amano K. Validity of a self-administered diet history questionnaire for assessment of sodium and potassium: comparison with single 24-hour urinary excretion. Jpn Circ J. 1998;62:431–5. [PubMed]
24. Sasaki S, Ushio F, Amano K, Morihara M, Todoriki T, Uehara Y, et al. Serum biomarker-based validation of a self-administered diet history questionnaire for Japanese subjects. J Nutr Sci Vitaminol. 2000;46:285–96. [PubMed]
25. Murakami K, Sasaki S, Takahashi Y, Okubo H, Hirota N, Notsu A, et al. Reproducibility and relative validity of dietary glycaemic index and load assessed with a self-administered diet-history questionnaire in Japanese adults. Br J Nutr. 2008;99:639–48. [PubMed]
26. Science and Technology Agency . Standard Tables of Food Composition in Japan, Fifth Revised and Enlarged Edition. Tokyo, Japan: Printing Bureau of the Ministry of Finance; 2005. (in Japanese)
27. Murakami K, Sasaki S, Takahashi Y, Okubo H, Hirota N, Notsu A, et al. Comparability of weighed dietary records and a self-administered diet history questionnaire for estimating monetary cost of dietary energy. Environmental Health Insights. 2008;1:35–43. http://www.la-press.com/article.php?article_id=1016 [PMC free article] [PubMed]
28. Price Statistics Office, Statistics Bureau National Retail Price Survey in JapanAvailable at: http://www.stat.go.jp/data/kouri/index.htm Accessed June 26, 2008 (in Japanese).
29. Murakami K, Sasaki S, Takahashi Y, Uenishi K, Yamasaki M, Hayabuchi H, et al. Misreporting of dietary energy, protein, potassium and sodium in relation to body mass index in young Japanese women. Eur J Clin Nutr. 2008;62:111–8. [PubMed]
30. Murakami K, Sasaki S, Takahashi Y, Uenishi K, for the Japan Dietetic Students’ Study for Nutrition and Biomarkers Group Dietary energy density is associated with body mass index and waist circumference, but not with other metabolic risk factors, in free-living young Japanese women. Nutrition. 2007;23:798–806. [PubMed]
31. Laaksonen M, Rahkonen O, Martikainen P, Lahelma E. Socioeconomic position and self-rated health: the contribution of childhood socioeconomic circumferences, adult socioeconomic status, and material resources. Am J Public Health. 2005;95:1403–9. [PubMed]
32. Ministry of Health, Labour, and Welfare of Japan . The National Nutrition Survey in Japan, 1955–2000. Tokyo, Japan: Ministry of Health and Welfare; 1957–2002. (in Japanese).
33. Ministry of Health, Labour, and Welfare Statistical tables: trend of medical expenditure, Gross National Product, and Net National Income in JapanAvailable at: http://www1.mhlw.go.jp/toukei/k-iryohi/hyo1.html Accessed June 26, 2008 (in Japanese).

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