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Food price trends in South Korea through time series analysis
p u b l i c h e a l t h 1 6 5 ( 2 0 1 8 ) 6 7 e7 3
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Original Research
Food price trends in South Korea through time series analysis T.H. Kim a,1, Y. Park b,1, J. Myung b, E. Han b,* a b
Graduate School of Public Health and Institute of Health Services Research, Yonsei University, Seoul, South Korea College of Pharmacy, Yonsei Institute of Pharmaceutical Sciences, Yonsei University, Incheon, South Korea
article info
abstract
Article history:
Objectives: This study analyzed the relative time trends of prices of healthy versus un-
Received 16 April 2018
healthy foods in South Korea for the 20 years from 1995 to 2015.
Received in revised form
Study design: Time series analysis was used.
14 August 2018
Methods: We analyzed price trends of selected food items in the food groups of grains,
Accepted 7 September 2018
vegetables, meats, sweets, spices, fast foods, and non-alcoholic beverages. We obtained nominal prices from the monthly reports of the 2006 Consumer Price Survey for representative items in each food group.
Keywords:
Results: The real price of processed meat increased by 1.2 percentage points less than the
Time trend
overall Consumer Price Index (CPI) increase, whereas beef prices increased by 2.4 per-
Food price
centage points more than the CPI increase. The price of soda was cheaper than that of
South Korea
other non-alcoholic beverages, whereas the real prices of milk showed statistically
Healthy foods
significantly larger yearly increases (by 1.4 percentage points, respectively) than that of the
Unhealthy foods
CPI. The yearly increases in the real prices of pizza, hamburgers, and fried chickendthree representative fast-food items that were mostly consumed by eating out or through home deliverydwere statistically significantly less than those of the CPI (by 1.5, 1.4, and 0.3 percentage points, respectively). Conclusions: Our results show that relatively healthy foods showed higher real price increases than the CPI increase, whereas the opposite occurred for unhealthy foods. © 2018 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.
Introduction Obesity has been a major public health concern in developed countries because of its high prevalence. Its prevalence has risen to the extent that the World Health Organization (WHO)
declared obesity a global epidemic.1 Its prevalence among adults in the US was 30.5% in 1999e2000, jumped to 34.3% in 2005e2006, and peaked at 37.7% in 2013e2014, the level that was most recently announced.2 Obesity is a well-recognized risk factor for various chronic diseases, such as high blood pressure, diabetes, and cardiovascular disorders, and even for
* Corresponding author. College of Pharmacy, Yonsei Institute of Pharmaceutical Sciences, Yonsei University, 162-1 Songdo-Dong, Yeonsu-Gu, Incheon, South Korea. Tel.: þ82 10 9334 7870; þ82 32 749 4511; fax: þ82 32 749 4105. E-mail address: [email protected] (E. Han). 1 These authors equally contributed to the manuscript. https://doi.org/10.1016/j.puhe.2018.09.007 0033-3506/© 2018 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.
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death.3 It consequently causes not only direct costs related to treating diseases, such as medical expenses and nursing fees, but also opportunity costs related to the occurrence of disease, such as productivity losses.4,5 Obesity has also increasingly been the core public health concern in developing or newly developed countries.1,6e8 A rise in obesity prevalence has also been observed in Korea, where almost a quarter (25.7% of men and 25.9% of women) of adults aged 19 years or older were categorized as obese (body mass index [BMI] 25 kg/m2) in 1998 compared with 32.8% in 2012 and 31.5% (37.7% of men and 25.3% of women) in 2014.9 These Korean trends imply that obesity is a core public health interest that should be prevented and effectively managed. The ultimate reason that people become obese is that they take in more calories than they use. Although individuals choose their caloric intake and consumption, studies have shown that environmental factors are important modifiers for individual choices.10 People encounter a food environment where affordable, high-calorie but low-nutrition foods are easily available because of advancements in food technologies.11,12 Increased time constraints due to more labor market participation among women and improved affordability also lead to eating out more frequently, where people tend to consume more than they would if they had eaten at home.13 At the same time, preferences for white-collar jobs and the corresponding sedentary lifestyles result in less excretion of calories.14,15 A large number of previous studies have observed such obesogenic environmental factors, and the majority of such studies focus on Western countries.16,17 However, the food environment has rapidly become globalized, and the obesogenic environment is no longer a concern for some developed countries alone. The relevant global evidence in Asian countries is still sparse, restraining our understanding of the underlying reason for the rise in obesity prevalence and corresponding public interventions to improve the situation in the region. This study contributes to the global evidence on the implicit magnitude of the obesogenic environment by analyzing the relative time trends of prices of selected foods in South Korea for the 20 years from 1995 to 2015. The findings of this study would help to guide policy interventions for food environments to prompt changes in individual choices for calorie consumption.
Methods We selected foods to investigate price changes over time based on previous studies18e21 on the obesogenic environment, focusing on food price. For this purpose, the food groups to be included in this study were determined as the following: grains, vegetables, meats, sweets, spices, fast foods, and nonalcoholic beverages.22 We then determined specific food items to include in each food group, as shown in Table 1. We obtained nominal food prices from the monthly report of the 2006 Consumer Price Survey for representative items in each food group. A unit of each item was transformed into 100 mL for liquids and 100 g for solids. We transformed each nominal price to real price by applying the yearly Consumer Price Index
Table 1 e Specific food items and food groups for the analysis. Food group Grains Staples Processed staples Vegetables
Meats and dairy Beverages Spices Sweets Fast food a
Items Rice, barley, beans Noodles, ramen, bread, rice cakes Cabbage, lettuce, daikon, bean sprouts, squash, green onions, onions, garlic Beef, pork, chicken, eggs, convenience meat (ham and sausages)a Milk, fruit juice, soymilk, water, soda Sugar, vegetable oil Chocolate, candy, ice cream, biscuits Fried chicken, hamburgers, pizza
Real prices between 1995 and 2015 were investigated instead of 1995e2015 because of data restrictions.
(CPI) for each food item, which we obtained from the Korean Statistical Information Service for the 20 years from 1995 to 2015 (except for convenience meats, which were measured between 2005 and 2015 because of data constraints), with 2010 as the reference year. We also standardized the real price of each food item relative to CPI for all items to address the relative change in a specific food price compared with the average change for all items. To estimate the yearly average change in the real price of each food price, we performed a series of ordinary least square regressions (OLS) on a linear year measurement for the following dependent variables: (1) CPI for all items (general CPI) and (2) a series of the real prices of each food item. All dependent variables were log transformed, and thus, 100 times the coefficient estimates on the linear year measurement denote the yearly average movement in percent of the general CPI or the real food prices of each food item. To assess the difference in the extent of the yearly average movement of the real food price of a food item from that of the general CPI, we additionally ran OLS for log-transformed ratio of the real food price of the food item to the general CPI. Given that the dependent variable is a logged form, 100 times the coefficient estimates from the additional regression approximate the subtraction of the percent change in the general CPI from the percent change in the real price of the food item. NeweyeWest standard errors were estimated for the regression coefficient estimates to account for possible autocorrelation in the errors.23 All analyses were performed using STATA, 13.1 (StataCorp, College Station, TX, USA). This study was reviewed by the Review Board of the Yonsei Institute of Pharmaceutical Sciences (7001988-201704-HR-175-01E).
Results Fig. 1 shows the price trends of the selected food items. Despite the overall increasing trend across foods, there are several variations by food items. The time trends of basic staples, such as rice, barley, and noodles, show stationary patterns, with the cheapest prices over time among the food items in this group, whereas the bean price has fluctuated over time (Fig. 1a). Most vegetable prices have barely changed
p u b l i c h e a l t h 1 6 5 ( 2 0 1 8 ) 6 7 e7 3
69
Fig. 1 e Yearly trends in inflation-adjusted food prices by the groups and items: (a) grains; (b) vegetables; (c) meats and dairy; (d) beverages; (e) sweets; and (f) fast foods.
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over time, and the real price levels have been less than 200 Korean won (approximately 0.2 US dollars). However, the prices of garlic and lettuce have increased remarkably over time, unlike the other vegetable items investigated (Fig. 1b). Meat prices also show two different patterns: the prices of chicken and eggs have been relatively stable over time, whereas the prices of beef, pork, and other convenience meats have been increasing overall. Sausages were more expensive than pork until 2001, but they became cheaper since 2003 (Fig. 1c). The price of soda decreased after 2000. The price of soda has been cheaper than that of other non-alcoholic beverages investigated, and the price gaps have become larger over time (Fig. 1d). The price trends of sweets have been generally stable, but their prices are more expensive than those of other produce and staples. The sugar price in particular shows almost no changes over time, with the price level remaining almost less than 0.1 US dollars (Fig. 1e). The prices of fast foods have increased. The price of fried chicken is the cheapest in this group, and its value has remained the same over the years. The rate of increase for these prices is also small (Fig. 1f). Table 2 shows the extent of the yearly increase in the real prices of food items of interest, each of which was compared with the yearly increase in the CPI. To begin with, the CPI increased 4.0% on average per year in Korea over the 20 years between 1995 and 2015. The real price has increased during this period for all food items of interest, not surprisingly, but the extent of yearly price growth has varied, with a maximum four-fold difference between food items. Most items in the staples group showed statistically significantly larger increases in real price compared with the CPI, with a maximum real price increase of 7.8% on average per year for beans, a 3.8 percentage point higher than the general CPI movement. Rice was the only exception that experienced a statistically significantly smaller real price increase per year than the general CPI, with a 3.3% yearly increase in real price. All vegetable items showed a larger real price increase than the general CPI, and such differences were statistically significant for all items investigated (Table 2). For the meat group, the real price of convenience meat, including ham and sausages, increased by only 3.4% on average per year, which was statistically significantly less (by 1.2 percentage points) than the general CPI increase. At the same time, the yearly price increase for beef was 6.5% on average per year, which was statistically significantly higher (by 2.4 percentage points) than the general CPI increase. The real prices for water increased by 1.2% on average per year, which was statistically significantly less than the increase in the general CPI by 1.9 percentage points. On the contrary, the real prices of milk showed statistically significantly larger yearly increases (by 1.4 percentage points) than did the CPI (Table 2). The increases in the real prices of sugar and vegetable oil were 3.1% and 3.7% on average, respectively, both of which were statistically significantly less than those of the CPI (by 1.4 and 0.8 percentage points, respectively), even though all of the food items in the sweets group had statistically significantly larger increases in real prices over these years than did the CPI. Finally, the yearly increases in the real prices of fried chicken, hamburgers, and pizza, the three representative fast-
food items that were mostly consumed by eating out or through home delivery, were compared with the increase in the CPI. All three showed statistically significantly smaller yearly increases in the real price on average, with the biggest difference for pizza (by 1.5 percentage points), followed by hamburgers (by 1.4 percentage points) and fried chicken (by 0.3 percentage points) (Table 2).
Discussion Food prices have been examined as a potential food environment to determine the BMI and the related risk for lifestyle disease.19,24e28 Studies particularly have focused on differences in the price patterns of healthy and unhealthy foods. Healthy foods with low calories and a high nutritional value are usually more expensive than unhealthy foods with high calories and a low nutrition value.10,18,29,30 Such a price differential between healthy versus unhealthy foods has increased over time as the prices of vegetables and fruits have increased but that of junk food has decreased.19, 27, 31e33 Despite the vast interest in the previous literature, there are few studies exploring the food price trends in Asian countries. This study fills the gap in the previous literature. Our findings show that, compared with the overall increase in the CPI, the prices of healthy foods (such as beef or milk) have increased more, whereas the prices of unhealthy foods (such as processed meats or fast food) have increased less. Particularly, processed meats and fast foods had smaller price increases over time compared with the general consumer price, as has been reported for several developed countries including the US and the UK34 Examining the pattern of changes in food prices over time helps us to implicitly understand the reasons behind the increase in obesity prevalence. If the prices of unhealthy foods have increased more slowly than the prices of healthy foods, we can consider relative changes in food prices over time as a potential driver of the rise in the obesity prevalence. This result would also provide insights into the consideration of executing any excise tax or subsidy for specific healthy foods to influence the food choices of consumers.35 However, the evidence of the effect of food prices on food consumption is haphazard, despite an enormous interest in the food environment including food prices with regard to obesity containment.36e38 Regardless, food prices are considered as a necessary element in a system-oriented approach, emphasizing the all-around interventions in terms of individual, social, and physical environments to tackle obesity.37 The consumption of processed foods and sugar-sweetened beverages has increased in developing countries39e42 and newly developed countries such as Korea.41 Traditional Korean diets are characterized by substantial vegetable intake (particularly garlic) and low intake of fats.42 Koreans have been trying to keep their traditional diet culture even amid a swift change in the external food environment43 that has paralleled the rapid Westernization and economic success over the decades.44 However, the processed food industry has grown rapidly in Korea as well, to the extent that domestic food processing companies in Korea increased their production by 9% in 2014 compared with 2013,45 and sales of
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Table 2 e Time series analysis on the extent of the average yearly movement in the Consumer Price Index and real prices of food items. Food group and items
Consumer Price Index Staples grains Rice Barley Beans Process staples grains Noodles Ramen Bread Rice cakes Vegetables Cabbage Lettuce Daikon Bean sprouts Squash Green onions Onions Garlic Meat and dairy Beef Pork Chicken Eggs Ham and sausagesc Beverages Milk Fruit juice Soymilk Water Soda Spices Sugar Vegetable oil Sweets Chocolate Candy Ice cream Biscuits Fast food Fried chicken Hamburgers Pizza
Dependent variables Log-transformed real price
Log-transformed ratio of the real price of to the Consumer Price Indexb
Coefficient (SE)c
Coefficient (SE)c
0.040**
(0.002)
e
e
0.033** 0.043** 0.078**
(0.003) (0.003) (0.005)
0.007** 0.003 0.038**
(0.002) (0.004) (0.003)
0.061** 0.045** 0.047** 0.055**
(0.002) (0.002) (0.001) (0.006)
0.021** 0.005 0.007** 0.015**
(0.002) (0.003) (0.002) (0.004)
0.063** 0.073** 0.059** 0.047** 0.060** 0.065** 0.052** 0.050**
(0.006) (0.005) (0.008) (0.002) (0.006) (0.006) (0.004) (0.005)
0.023** 0.033** 0.019** 0.008** 0.020** 0.025** 0.013** 0.011*
(0.005) (0.003) (0.006) (0.001) (0.004) (0.004) (0.004) (0.005)
0.065** 0.045** 0.040** 0.047** 0.034**
(0.006) (0.003) (0.002) (0.002) (0.003)
0.024** 0.001 0.003 0.002 0.012**
(0.002) (0.004) (0.002) (0.003) (0.003)
0.054** 0.036** 0.047** 0.012** 0.041**
(0.001) (0.002) (0.002) (0.002) (0.002)
0.014** 0.001 0.007 0.019** 0.001
(0.002) (0.003) (0.003) (0.002) (0.004)
0.031** 0.037**
(0.004) (0.003)
0.014* 0.008*
(0.006) (0.005)
0.047** 0.054** 0.054** 0.077**
(0.002) (0.002) (0.002) (0.003)
0.002 0.007 0.014** 0.028**
(0.003) (0.004) (0.002) (0.005)
0.038** 0.026** 0.025**
(0.002) (0.002) (0.001)
0.003** 0.014** 0.015**
(0.001) (0.002) (0.002)
SE, standard error. a Coefficient in each row is from a regression of the log-transformed ratio of the real price of each food item to the CPI on the linear measurement of year with the NeweyeWest standard errors in parenthesis. Therefore, it denotes the absolute difference in the relative yearly average change in the real price of the corresponding food item from the relative yearly average change in the CPI. b Real price between 2005 and 2015 were investigated instead of 2005e2015 because of data restrictions. c *P < 0.05,** P < 0.01.
processed food in Korea comprised 54.6% of the total food market in 2014.46 A handful of previous studies have assessed the obesogenic food environment with aggregated food price data in a similar vein to this study. For example, Wendt and Todd (2011)19 used real food price data from the Bureau of Labor Statistics in the US between 1980 and 2010 and aggregated the food price as an annual average for urban consumers. Powell
et al. (2013)27 also used aggregated time trends of real food prices between 1980 and 2011, reporting a rise in real prices for fruits and vegetables and a fall for unhealthy foods such as carbonated drinks. Aggregated food price data were also used to assess their association with individual-level body weight outcomes in the previous literature. For example, Powell and Han (2011)48 reported a time series of real food price data that were aggregated at the zip code level and assessed whether
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food at home versus food away from home prices affect the adolescent's body weight status. Powell (2009)47 also used county-level aggregated fast-food price data to evaluate its association with adolescents' BMI. However, we acknowledge that the present study does not explicitly link food price changes to the obesity increase in Korea and uses highly aggregated data. Despite such a limitation, it is important to consider the relative paucity of previous studies on the relevant issue in the AsiaePacific region where parallel changes in obesity prevalence and the obesogenic food environment have been continuously observed. Our manuscript contributes to the previous literature by expanding the realm of the study and generating a potential reason to explain such trends in the region and thus, raises an interesting clue for future studies. Building on this study, the future studies need to investigate the extent to which such changes in the food environment have actually contributed to individual food consumption behaviors and consequent body mass changes.
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Author statements
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Ethical approval
12.
The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008.
14.
Funding
15.
Research support from the Korea National Research Foundation (2017R1A2B4003373) is gratefully acknowledged. The content is solely the responsibility of the authors and does not necessarily represent the official view of the Korea National Research Foundation. The Korea National Research Foundation had no involvement in preparation and submission of this manuscript.
Competing interests
13.
16.
17.
18.
None declared.
Author contributions E.H. formulated the research question, designed the study, oversighted the data analysis, and wrote the article. T.H.K. helped formulation of research question and wrote the article. Y.J.P. performed the data analysis and drafted the preliminary version of the article. J.E.M. performed the data analysis.
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20. 21.
22.
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25. Goldman D, Lakdawalla D, Zheng Y. Food prices and the dynamics of body weight. NBER Working Paper No. 15096. Cambridge, MA: National Bureau of Economic Research; 2009. 26. Powell LM, Auld MC, Chaloupka FJ, O'Malley PM, Johnston LD. Access to fast food and food prices: relationship with fruit and vegetable consumption and overweight among adolescents. In: Bolin Kristian, Cawley John, editors, editors. The economics of obesity. Emerald Group Publishing Limited; 2006. p. 23e48. 27. Powell LM, Chriqui JF, Khan T Wada R, Chaloupka FJ. Assessing the potential effectiveness of food and beverage taxes and subsidies for improving public health: a systematic review of prices, demand and body weight outcomes. Obes Rev 2013;14:110e28. 28. Powell LM, Zhao Z, Wang Y. Food prices and fruit and vegetable consumption among young American adults. Health Place 2009;15:1064e70. 29. Aggarwal A, Monsivais P, Drewnowski A. Nutrient intakes linked to better health outcomes are associated with higher diet costs in the US. PLoS One 2012;7:e37533. 30. Connell CL, Zoellner JM, Yadrick MK, Chekuri SC, Crook LB, Bogle ML. Energy density, nutrient adequacy, and cost per serving can provide insight into food choices in the lower Mississippi Delta. J Nutr Educ Behav 2012;44:148e53. 31. Capacci S, Mazzocchi M, Shankar B. The regional price of junk foods relative to healthy foods in the UK: indirect estimation of a time series, 1997-2009. In: 86th AES annual conference. UK: Warwick University; 2012. p. 16e8. 32. Gelbach JB, Klick J, Stratmann T. Cheap donuts and expensive broccoli: the effect of relative prices on obesity. December 15, 2009. Available at SSRN: https://ssrn.com/abstract=976484 or http:// dx.doi.org/10.2139/ssrn.976484. 33. Monsivais P, Drewnowski A. The rising cost of low-energydensity foods. J Am Diet Assoc 2007;107:2071e6. 34. Claro RM, Monteiro CA. Renda familiar, prec¸o de alimentos e ~ o domiciliar de frutas e hortalic¸as no Brasil. Rev Saude aquisic¸a Publica 2012;44:1014e20. 35. Briggs AD, Mytton OT, Kehlbacher A, Tiffin R, Rayner M, Scarborough P. Overall and income specific effect on prevalence of overweight and obesity of 20% sugar sweetened drink tax in UK: econometric and comparative risk assessment modelling study. BMJ 2013;347:f6189.
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36. Cobb L, Appel LJ, Franco M, Jones-Smith JC, Nur A, Anderson CA. The relationship of the local food environment with obesity: a systematic review of methods, study quality, and results. Obesity (Silver Spring) 2015;23(7):1331e44. 37. Finkelstein EA, Strombotne KL, Zhen C, Epstein LH. Food prices and obesity. Adv Nutr 2014;5:818e21. 38. Mattes R, Foster GD. Food environment and obesity. Obesity (Silver Spring) 2014;22(12):2459e61. 39. Barretto SAJ, Cyrillo DC. Analysis of household expenditures with food in the city of S. Paulo in the 1990's. Rev Saude Publica 2001;35:52e9. 40. Basu S, Yoffe P, Hills N Lustig RH. The relationship of sugar to population-level diabetes prevalence: an econometric analysis of repeated cross-sectional data. PLoS One 2013;8:e57873. 41. Han E, Kim TH, Powell LM. Beverage consumption and individual-level associations in South Korea. BMC Pub Health 2013;13:195. 42. Monteiro CA, Moubarac JC, Cannon G, Ng SW, Popkin B. Ultraprocessed products are becoming dominant in the global food system. Obes Rev 2013;14:21e8. 43. Lee HS, Duffey KJ, Popkin BM. South Korea's entry to the global food economy: shifts in consumption of food between 1998 and 2009. Asia Pac J Clin Nutr 2012;21:618e29. 44. Lee M-J, Popkin BM, Kim S. The unique aspects of the nutrition transition in South Korea: the retention of healthful elements in their traditional diet. Publ Health Nutr 2012;5:197e203. 45. Korea Health Industry Development Institute. Food industry analysis report in 2015. 2015. https://www.khidi.or.kr/ fileDownload?titleId¼138551&fileId¼1&fileDownType¼ C¶mMenuId¼MENU00085. [Accessed April 2017]. 46. Chio JH. Analysis of domestic and foreign food market and implications. 2016. https://rd.kdb.co.kr/er/wcms.do? actionId¼ADERERERWCE93&contentPage¼/er/er/er/ ERER27I00010_01RS_DWIFRAME.jsp&cid¼21019. [Accessed April 2017]. 47. Powell LM. Fast food costs and adolescent body mass index: evidence from panel data. J Health Econ 2009;28(5):963e70. 48. Powell LM, Han E. The costs of food at home and away from home and consumption patterns among U.S. adolescents. J Adolesc Health 2011;48(1):20e6.
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Public Health journal homepage: www.elsevier.com/puhe
Original Research
Food price trends in South Korea through time series analysis T.H. Kim a,1, Y. Park b,1, J. Myung b, E. Han b,* a b
Graduate School of Public Health and Institute of Health Services Research, Yonsei University, Seoul, South Korea College of Pharmacy, Yonsei Institute of Pharmaceutical Sciences, Yonsei University, Incheon, South Korea
article info
abstract
Article history:
Objectives: This study analyzed the relative time trends of prices of healthy versus un-
Received 16 April 2018
healthy foods in South Korea for the 20 years from 1995 to 2015.
Received in revised form
Study design: Time series analysis was used.
14 August 2018
Methods: We analyzed price trends of selected food items in the food groups of grains,
Accepted 7 September 2018
vegetables, meats, sweets, spices, fast foods, and non-alcoholic beverages. We obtained nominal prices from the monthly reports of the 2006 Consumer Price Survey for representative items in each food group.
Keywords:
Results: The real price of processed meat increased by 1.2 percentage points less than the
Time trend
overall Consumer Price Index (CPI) increase, whereas beef prices increased by 2.4 per-
Food price
centage points more than the CPI increase. The price of soda was cheaper than that of
South Korea
other non-alcoholic beverages, whereas the real prices of milk showed statistically
Healthy foods
significantly larger yearly increases (by 1.4 percentage points, respectively) than that of the
Unhealthy foods
CPI. The yearly increases in the real prices of pizza, hamburgers, and fried chickendthree representative fast-food items that were mostly consumed by eating out or through home deliverydwere statistically significantly less than those of the CPI (by 1.5, 1.4, and 0.3 percentage points, respectively). Conclusions: Our results show that relatively healthy foods showed higher real price increases than the CPI increase, whereas the opposite occurred for unhealthy foods. © 2018 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.
Introduction Obesity has been a major public health concern in developed countries because of its high prevalence. Its prevalence has risen to the extent that the World Health Organization (WHO)
declared obesity a global epidemic.1 Its prevalence among adults in the US was 30.5% in 1999e2000, jumped to 34.3% in 2005e2006, and peaked at 37.7% in 2013e2014, the level that was most recently announced.2 Obesity is a well-recognized risk factor for various chronic diseases, such as high blood pressure, diabetes, and cardiovascular disorders, and even for
* Corresponding author. College of Pharmacy, Yonsei Institute of Pharmaceutical Sciences, Yonsei University, 162-1 Songdo-Dong, Yeonsu-Gu, Incheon, South Korea. Tel.: þ82 10 9334 7870; þ82 32 749 4511; fax: þ82 32 749 4105. E-mail address: [email protected] (E. Han). 1 These authors equally contributed to the manuscript. https://doi.org/10.1016/j.puhe.2018.09.007 0033-3506/© 2018 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.
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death.3 It consequently causes not only direct costs related to treating diseases, such as medical expenses and nursing fees, but also opportunity costs related to the occurrence of disease, such as productivity losses.4,5 Obesity has also increasingly been the core public health concern in developing or newly developed countries.1,6e8 A rise in obesity prevalence has also been observed in Korea, where almost a quarter (25.7% of men and 25.9% of women) of adults aged 19 years or older were categorized as obese (body mass index [BMI] 25 kg/m2) in 1998 compared with 32.8% in 2012 and 31.5% (37.7% of men and 25.3% of women) in 2014.9 These Korean trends imply that obesity is a core public health interest that should be prevented and effectively managed. The ultimate reason that people become obese is that they take in more calories than they use. Although individuals choose their caloric intake and consumption, studies have shown that environmental factors are important modifiers for individual choices.10 People encounter a food environment where affordable, high-calorie but low-nutrition foods are easily available because of advancements in food technologies.11,12 Increased time constraints due to more labor market participation among women and improved affordability also lead to eating out more frequently, where people tend to consume more than they would if they had eaten at home.13 At the same time, preferences for white-collar jobs and the corresponding sedentary lifestyles result in less excretion of calories.14,15 A large number of previous studies have observed such obesogenic environmental factors, and the majority of such studies focus on Western countries.16,17 However, the food environment has rapidly become globalized, and the obesogenic environment is no longer a concern for some developed countries alone. The relevant global evidence in Asian countries is still sparse, restraining our understanding of the underlying reason for the rise in obesity prevalence and corresponding public interventions to improve the situation in the region. This study contributes to the global evidence on the implicit magnitude of the obesogenic environment by analyzing the relative time trends of prices of selected foods in South Korea for the 20 years from 1995 to 2015. The findings of this study would help to guide policy interventions for food environments to prompt changes in individual choices for calorie consumption.
Methods We selected foods to investigate price changes over time based on previous studies18e21 on the obesogenic environment, focusing on food price. For this purpose, the food groups to be included in this study were determined as the following: grains, vegetables, meats, sweets, spices, fast foods, and nonalcoholic beverages.22 We then determined specific food items to include in each food group, as shown in Table 1. We obtained nominal food prices from the monthly report of the 2006 Consumer Price Survey for representative items in each food group. A unit of each item was transformed into 100 mL for liquids and 100 g for solids. We transformed each nominal price to real price by applying the yearly Consumer Price Index
Table 1 e Specific food items and food groups for the analysis. Food group Grains Staples Processed staples Vegetables
Meats and dairy Beverages Spices Sweets Fast food a
Items Rice, barley, beans Noodles, ramen, bread, rice cakes Cabbage, lettuce, daikon, bean sprouts, squash, green onions, onions, garlic Beef, pork, chicken, eggs, convenience meat (ham and sausages)a Milk, fruit juice, soymilk, water, soda Sugar, vegetable oil Chocolate, candy, ice cream, biscuits Fried chicken, hamburgers, pizza
Real prices between 1995 and 2015 were investigated instead of 1995e2015 because of data restrictions.
(CPI) for each food item, which we obtained from the Korean Statistical Information Service for the 20 years from 1995 to 2015 (except for convenience meats, which were measured between 2005 and 2015 because of data constraints), with 2010 as the reference year. We also standardized the real price of each food item relative to CPI for all items to address the relative change in a specific food price compared with the average change for all items. To estimate the yearly average change in the real price of each food price, we performed a series of ordinary least square regressions (OLS) on a linear year measurement for the following dependent variables: (1) CPI for all items (general CPI) and (2) a series of the real prices of each food item. All dependent variables were log transformed, and thus, 100 times the coefficient estimates on the linear year measurement denote the yearly average movement in percent of the general CPI or the real food prices of each food item. To assess the difference in the extent of the yearly average movement of the real food price of a food item from that of the general CPI, we additionally ran OLS for log-transformed ratio of the real food price of the food item to the general CPI. Given that the dependent variable is a logged form, 100 times the coefficient estimates from the additional regression approximate the subtraction of the percent change in the general CPI from the percent change in the real price of the food item. NeweyeWest standard errors were estimated for the regression coefficient estimates to account for possible autocorrelation in the errors.23 All analyses were performed using STATA, 13.1 (StataCorp, College Station, TX, USA). This study was reviewed by the Review Board of the Yonsei Institute of Pharmaceutical Sciences (7001988-201704-HR-175-01E).
Results Fig. 1 shows the price trends of the selected food items. Despite the overall increasing trend across foods, there are several variations by food items. The time trends of basic staples, such as rice, barley, and noodles, show stationary patterns, with the cheapest prices over time among the food items in this group, whereas the bean price has fluctuated over time (Fig. 1a). Most vegetable prices have barely changed
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Fig. 1 e Yearly trends in inflation-adjusted food prices by the groups and items: (a) grains; (b) vegetables; (c) meats and dairy; (d) beverages; (e) sweets; and (f) fast foods.
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over time, and the real price levels have been less than 200 Korean won (approximately 0.2 US dollars). However, the prices of garlic and lettuce have increased remarkably over time, unlike the other vegetable items investigated (Fig. 1b). Meat prices also show two different patterns: the prices of chicken and eggs have been relatively stable over time, whereas the prices of beef, pork, and other convenience meats have been increasing overall. Sausages were more expensive than pork until 2001, but they became cheaper since 2003 (Fig. 1c). The price of soda decreased after 2000. The price of soda has been cheaper than that of other non-alcoholic beverages investigated, and the price gaps have become larger over time (Fig. 1d). The price trends of sweets have been generally stable, but their prices are more expensive than those of other produce and staples. The sugar price in particular shows almost no changes over time, with the price level remaining almost less than 0.1 US dollars (Fig. 1e). The prices of fast foods have increased. The price of fried chicken is the cheapest in this group, and its value has remained the same over the years. The rate of increase for these prices is also small (Fig. 1f). Table 2 shows the extent of the yearly increase in the real prices of food items of interest, each of which was compared with the yearly increase in the CPI. To begin with, the CPI increased 4.0% on average per year in Korea over the 20 years between 1995 and 2015. The real price has increased during this period for all food items of interest, not surprisingly, but the extent of yearly price growth has varied, with a maximum four-fold difference between food items. Most items in the staples group showed statistically significantly larger increases in real price compared with the CPI, with a maximum real price increase of 7.8% on average per year for beans, a 3.8 percentage point higher than the general CPI movement. Rice was the only exception that experienced a statistically significantly smaller real price increase per year than the general CPI, with a 3.3% yearly increase in real price. All vegetable items showed a larger real price increase than the general CPI, and such differences were statistically significant for all items investigated (Table 2). For the meat group, the real price of convenience meat, including ham and sausages, increased by only 3.4% on average per year, which was statistically significantly less (by 1.2 percentage points) than the general CPI increase. At the same time, the yearly price increase for beef was 6.5% on average per year, which was statistically significantly higher (by 2.4 percentage points) than the general CPI increase. The real prices for water increased by 1.2% on average per year, which was statistically significantly less than the increase in the general CPI by 1.9 percentage points. On the contrary, the real prices of milk showed statistically significantly larger yearly increases (by 1.4 percentage points) than did the CPI (Table 2). The increases in the real prices of sugar and vegetable oil were 3.1% and 3.7% on average, respectively, both of which were statistically significantly less than those of the CPI (by 1.4 and 0.8 percentage points, respectively), even though all of the food items in the sweets group had statistically significantly larger increases in real prices over these years than did the CPI. Finally, the yearly increases in the real prices of fried chicken, hamburgers, and pizza, the three representative fast-
food items that were mostly consumed by eating out or through home delivery, were compared with the increase in the CPI. All three showed statistically significantly smaller yearly increases in the real price on average, with the biggest difference for pizza (by 1.5 percentage points), followed by hamburgers (by 1.4 percentage points) and fried chicken (by 0.3 percentage points) (Table 2).
Discussion Food prices have been examined as a potential food environment to determine the BMI and the related risk for lifestyle disease.19,24e28 Studies particularly have focused on differences in the price patterns of healthy and unhealthy foods. Healthy foods with low calories and a high nutritional value are usually more expensive than unhealthy foods with high calories and a low nutrition value.10,18,29,30 Such a price differential between healthy versus unhealthy foods has increased over time as the prices of vegetables and fruits have increased but that of junk food has decreased.19, 27, 31e33 Despite the vast interest in the previous literature, there are few studies exploring the food price trends in Asian countries. This study fills the gap in the previous literature. Our findings show that, compared with the overall increase in the CPI, the prices of healthy foods (such as beef or milk) have increased more, whereas the prices of unhealthy foods (such as processed meats or fast food) have increased less. Particularly, processed meats and fast foods had smaller price increases over time compared with the general consumer price, as has been reported for several developed countries including the US and the UK34 Examining the pattern of changes in food prices over time helps us to implicitly understand the reasons behind the increase in obesity prevalence. If the prices of unhealthy foods have increased more slowly than the prices of healthy foods, we can consider relative changes in food prices over time as a potential driver of the rise in the obesity prevalence. This result would also provide insights into the consideration of executing any excise tax or subsidy for specific healthy foods to influence the food choices of consumers.35 However, the evidence of the effect of food prices on food consumption is haphazard, despite an enormous interest in the food environment including food prices with regard to obesity containment.36e38 Regardless, food prices are considered as a necessary element in a system-oriented approach, emphasizing the all-around interventions in terms of individual, social, and physical environments to tackle obesity.37 The consumption of processed foods and sugar-sweetened beverages has increased in developing countries39e42 and newly developed countries such as Korea.41 Traditional Korean diets are characterized by substantial vegetable intake (particularly garlic) and low intake of fats.42 Koreans have been trying to keep their traditional diet culture even amid a swift change in the external food environment43 that has paralleled the rapid Westernization and economic success over the decades.44 However, the processed food industry has grown rapidly in Korea as well, to the extent that domestic food processing companies in Korea increased their production by 9% in 2014 compared with 2013,45 and sales of
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Table 2 e Time series analysis on the extent of the average yearly movement in the Consumer Price Index and real prices of food items. Food group and items
Consumer Price Index Staples grains Rice Barley Beans Process staples grains Noodles Ramen Bread Rice cakes Vegetables Cabbage Lettuce Daikon Bean sprouts Squash Green onions Onions Garlic Meat and dairy Beef Pork Chicken Eggs Ham and sausagesc Beverages Milk Fruit juice Soymilk Water Soda Spices Sugar Vegetable oil Sweets Chocolate Candy Ice cream Biscuits Fast food Fried chicken Hamburgers Pizza
Dependent variables Log-transformed real price
Log-transformed ratio of the real price of to the Consumer Price Indexb
Coefficient (SE)c
Coefficient (SE)c
0.040**
(0.002)
e
e
0.033** 0.043** 0.078**
(0.003) (0.003) (0.005)
0.007** 0.003 0.038**
(0.002) (0.004) (0.003)
0.061** 0.045** 0.047** 0.055**
(0.002) (0.002) (0.001) (0.006)
0.021** 0.005 0.007** 0.015**
(0.002) (0.003) (0.002) (0.004)
0.063** 0.073** 0.059** 0.047** 0.060** 0.065** 0.052** 0.050**
(0.006) (0.005) (0.008) (0.002) (0.006) (0.006) (0.004) (0.005)
0.023** 0.033** 0.019** 0.008** 0.020** 0.025** 0.013** 0.011*
(0.005) (0.003) (0.006) (0.001) (0.004) (0.004) (0.004) (0.005)
0.065** 0.045** 0.040** 0.047** 0.034**
(0.006) (0.003) (0.002) (0.002) (0.003)
0.024** 0.001 0.003 0.002 0.012**
(0.002) (0.004) (0.002) (0.003) (0.003)
0.054** 0.036** 0.047** 0.012** 0.041**
(0.001) (0.002) (0.002) (0.002) (0.002)
0.014** 0.001 0.007 0.019** 0.001
(0.002) (0.003) (0.003) (0.002) (0.004)
0.031** 0.037**
(0.004) (0.003)
0.014* 0.008*
(0.006) (0.005)
0.047** 0.054** 0.054** 0.077**
(0.002) (0.002) (0.002) (0.003)
0.002 0.007 0.014** 0.028**
(0.003) (0.004) (0.002) (0.005)
0.038** 0.026** 0.025**
(0.002) (0.002) (0.001)
0.003** 0.014** 0.015**
(0.001) (0.002) (0.002)
SE, standard error. a Coefficient in each row is from a regression of the log-transformed ratio of the real price of each food item to the CPI on the linear measurement of year with the NeweyeWest standard errors in parenthesis. Therefore, it denotes the absolute difference in the relative yearly average change in the real price of the corresponding food item from the relative yearly average change in the CPI. b Real price between 2005 and 2015 were investigated instead of 2005e2015 because of data restrictions. c *P < 0.05,** P < 0.01.
processed food in Korea comprised 54.6% of the total food market in 2014.46 A handful of previous studies have assessed the obesogenic food environment with aggregated food price data in a similar vein to this study. For example, Wendt and Todd (2011)19 used real food price data from the Bureau of Labor Statistics in the US between 1980 and 2010 and aggregated the food price as an annual average for urban consumers. Powell
et al. (2013)27 also used aggregated time trends of real food prices between 1980 and 2011, reporting a rise in real prices for fruits and vegetables and a fall for unhealthy foods such as carbonated drinks. Aggregated food price data were also used to assess their association with individual-level body weight outcomes in the previous literature. For example, Powell and Han (2011)48 reported a time series of real food price data that were aggregated at the zip code level and assessed whether
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food at home versus food away from home prices affect the adolescent's body weight status. Powell (2009)47 also used county-level aggregated fast-food price data to evaluate its association with adolescents' BMI. However, we acknowledge that the present study does not explicitly link food price changes to the obesity increase in Korea and uses highly aggregated data. Despite such a limitation, it is important to consider the relative paucity of previous studies on the relevant issue in the AsiaePacific region where parallel changes in obesity prevalence and the obesogenic food environment have been continuously observed. Our manuscript contributes to the previous literature by expanding the realm of the study and generating a potential reason to explain such trends in the region and thus, raises an interesting clue for future studies. Building on this study, the future studies need to investigate the extent to which such changes in the food environment have actually contributed to individual food consumption behaviors and consequent body mass changes.
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8. 9. 10.
Author statements
11.
Ethical approval
12.
The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008.
14.
Funding
15.
Research support from the Korea National Research Foundation (2017R1A2B4003373) is gratefully acknowledged. The content is solely the responsibility of the authors and does not necessarily represent the official view of the Korea National Research Foundation. The Korea National Research Foundation had no involvement in preparation and submission of this manuscript.
Competing interests
13.
16.
17.
18.
None declared.
Author contributions E.H. formulated the research question, designed the study, oversighted the data analysis, and wrote the article. T.H.K. helped formulation of research question and wrote the article. Y.J.P. performed the data analysis and drafted the preliminary version of the article. J.E.M. performed the data analysis.
19.
20. 21.
22.
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