Beverage consumption and individual-level associations in South Korea

Obesity has emerged as a global public health concern due to an increase in obesity prevalence in both developing and developed countries [1]. The obesity rate has increased more than three-fold since 1980 worldwide [2]. In the United States, the problem of obesity has been considered epidemic with 72% and 64% of adult men and women estimated to be overweight (body mass index (BMI) ≥ 25 kg/m²) and approximately one-third of adults estimated to be obese (BMI ≥ 30 kg/m²) in 2008 [3, 4]. The obesity prevalence in Korea is not as dramatic as in the United States; however, the prevalence of those overweight reached 31.7% in 2007, an increase from 29.2% in 2005 and 26.0% in 1998. For children and adolescents less than 20 years of age, the prevalence of obesity in Korea doubled over the last decade from 5.8% in 1997 to 10.9% in 2007 [5].

Coincident with the increasing trend of obesity prevalence, previous studies have reported an upward trend in the prevalence of sugar-sweetened beverage (SSB) consumption and the percentage of total energy intake derived from SSBs, including soft drinks and fruit drinks [3, 6–9]. The caloric intake of SSBs increased by 135% between 1977 and 2001 in all age groups in the United States [10] although a recent study reported that energy intake from SSBs overall decreased between 1999-2000 and 2007-2008 [11]. SSB sales data also indicated a parallel increase of SSB consumption through to the mid 2000’s with over 14 billion gallons of SSBs being sold in 2008 in the United States [12]. The SSB market has also increased greatly in Korea with total sales of approximately 2.9 billion US dollars in 2008 up from 2.0 billion US dollars in 1999 [13]. SSB consumption has been associated with higher energy intake, reduced consumption of healthier beverages such as milk, reduced nutrient intake, and increased incidence of negative health outcomes such as obesity, type II diabetes [14–17], bone loss [18], heart disease [19], and dental caries [20]. Studies mainly in the U.S. also reported that being non-Hispanic Black [11, 21–24], low education [11, 25–27], and low income [11, 23, 24, 28] were positively associated with SSB consumption.

Dietary patterns in developing countries such as China and Mexico have experienced a partial transition toward more unhealthy food consumption such as high consumption of fast food and SSBs [29]. However, despite that SSB consumption has been one of the most targeted plausible sources of the obesity epidemic [6] which has been a global phenomenon [2], data for non-US countries are limited and only a few previous studies have explored the nature of SSB consumption outside the U.S. including in Australia and the United Kingdom [25, 26, 30]. A recent study by Lee and colleagues (2012) explored the consumption trends of food including SSBs between 1998 and 2009 in South Korea, reporting that daily caloric intake from SSBs statistically significantly increased particularly among adolescents aged 13 to 18 and adults aged 19 and 39 years old [31]. Our study builds on the previous literature and investigates the nature of SSB consumption in South Korea, one of the fastest growing developed economies in this millennium [32] with rapid westernization in overall dietary patterns [33]. Understanding the determinants of SSB consumption in a global perspective is important to coordinate global policy measures and to combat obesity. This study provides recent evidence on beverage consumption patterns from 2001 to 2009 for overall and subtypes of SSBs and for milk as a comparable healthy beverage in South Korea. In a multivariate regression framework, we also explore individual-level socioeconomic factors associated with SSB consumption in South Korea.

Changes in the prevalence of beverage consumption over time

Miscellaneous SSBs including sports/energy drinks, coffee/tea products, flavored milk and other SSBs were the most prevalent beverage type in both 2001 and 2009 in all age groups except for adolescents with statistically significant increases in prevalence among adults (from 62% to 69%) and the elderly (from 30% to 47%). Milk was the most prevalent beverage consumed for adolescents and the next most consumed in older age groups in both 2001 and 2009 of which the prevalence statistically significantly increased among young adults (from 24% to 32%) and adults (from 18% to 22%). Although the prevalence levels for fruit drinks were not as high as other beverage types, its prevalence increased the most between 2001 and 2009 in all age groups (adolescents 5% to 14%; young adults 7% to 15%; adults 4% to 8%; and the elderly 3% to 6%). The prevalence of soda consumption statistically significantly increased only among young adults (from 14% to 19%), whereas it statistically significantly decreased among adolescents (from 22% to 18%) between 2001 and 2009 (see Figure 1).

Changes in caloric intake from beverages among consumers over time

The amount of caloric intake conditional on consumption increased for all beverage types in all age groups with the extent of the increase overall being larger for SSBs than milk. Among young adults, adults, and the elderly, the amount of calories consumed from regular soda and fruit drinks were generally much larger than from miscellaneous SSBs despite that they were not as prevalent as miscellaneous SSBs. In contrast, adolescents obtained the most calories from miscellaneous SSB among all beverage types, although its prevalence was lower than regular soda and milk in both 2001 and 2009. Young adults consumed 141.9 kcal of regular soda in 2009, which statistically significantly increased from 117.7 kcal in 2001. The amount of calories from fruit drinks nearly doubled among adolescents (63.0 to 126.8 kcal), young adults (64.7 to 135.5 kcal), adults (66.2 to 121.5 kcal), and the elderly (from 79.1 to 137.3 kcal), surpassing caloric intake from regular soda in 2009 (except for adolescents). Consumers of miscellaneous SSBs doubled their energy intake from it in 2009 (249.0, 76.4, 71.8, and 55.4 kcal for adolescents, young adults, adults, and the elderly, respectively) as compared to 2001 (167.1, 34.4, 29.8, and 20.2 kcal for adolescents, young adults, adults, and the elderly, respectively). The calories consumed from milk were larger than SSBs in both 2001 and 2009 in all age groups and increased statistically significantly among adolescents (164.8 to 200.4 kcal) young adults (140.5 kcal to 182.7 kcal) and adults (127.9 kcal to 150.6 kcal) (see Figure 2).

Previous studies have documented that the nutrition patterns for major food groups in South Korea have been under a remarkable transition toward more westernized diets over the past few decades [31, 35–38]. Our study findings for SSBs based on nationally representative data in South Korea showed that the prevalence of SSB consumption statistically significantly increased among adolescents (31% to 38%), young adults (66% to 69%), adults (63% 70%) and the elderly (31% to 50%) between 2001 and 2009. Our results are comparable to the recent report that between 1998 and 2009 caloric intake from SSBs has increased among adolescents and young to middle-aged adults between 13 and 40 years old [30]. Given that such increases happened in less than a decade, the rate of increase was actually more rapid than that in the U.S. [11, 16, 39].

However, notably in South Korea, the prevalence of milk consumption also statistically significantly increased between 2001 and 2009 among young adults (24% to 32%) and adults (18% to 22%), although the amount of caloric intake from milk among consumers was less than SSBs. Among adolescents, milk remained the most prevalently consumed beverage in both 2001 and 2009 with no statically significant change between the two time points. Whereas soda has been the most prevalent SSB in the United States in general [11], in South Korea miscellaneous SSBs (sports/energy drinks, coffee/tea products, flavored milk, and others) were the most prevalently consumed and their prevalence statistically significantly increased among adults (62% to 69%) and the elderly (30% to 47%) between 2001 and 2009. Although recent evidence shows that from 1999 to 2008 SSB consumption overall has fallen in the U.S., the prevalence of sports drink consumption increased significantly across all age groups, particularly among adolescents [11]. Our findings are parallel to the recent report that miscellaneous SSBs were the largest source of sugars consumed from processed foods in 2008-2010 for adults in Korea [40], and caloric intake from coffee and tea products increased more than tripled among individuals aged 40-59 between 1998 and 2009 [31].

This present study also found that individuals with higher income (both women and men) and higher education (men only for the prevalence and women only for calorie amount) showed higher odds of SSB consumption and caloric intake from SSBs. However, SES associations with overall caloric intake were quite small. Women and men in the top-income group were more likely to consume SSBs (OR = 1.18 for women and 1.25 for men), although they consumed overall just 4.0 and 2.7 more kcal per day than their counterparts in the bottom-income group. Such findings differ from other studies particularly in the U.S. that have reported higher odds of consumption and higher caloric intake among people in low SES [23, 26, 27, 41]. Our findings imply that increased public health efforts to improve the awareness of the potential negative effects of SSB consumption would be needed in Asian countries including South Korea given the dietary transitions with increasing popularity of western-style meals, particularly among children and adolescents in many developing countries [29].

It is a strength of our study that we estimated individual-level associations for the overall amount of consumption, which accounted for distributional characteristics of the amount of caloric intake as a mix of discrete and continuous forms. Continuous utilization magnitudes were observed only when actual utilization occurred [42, 43], and our data showed a sizable segment of the population who actually did not consume the beverages examined in this study. Therefore, a differential consumption probability should be taken into consideration to estimate the overall amount of use in terms of calories.

At the same time, study limitations should be considered in the interpretation of our results. First, our data, KNHANES, had detailed dietary recall information for a 24-hour period similar to the NHANES data in the U.S. However, due to the Korean dining culture in which all main dishes at the same table are typically shared, accurate data on food consumption at the individual level are limited to some extent. KNHANES used individual conversion factors based on age and gender to provide food consumption information at an individual level [44]. The extent to which this conversion represented real individual-level food consumption is not known. At the same time, individually packaged drinks are less likely to be shared, although we could not identify the unit of sales of SSBs in our analyses. Second, we pooled five waves of the KNHANES data including 2001, 2005, 2007, 2008, and 2009, among which seasonally weighted data were not collected for the 2001 and 2005 waves [31]. Third, due to relatively small sample sizes in each survey round, we were unable to estimate differences in individual-level specific associations over time, although we controlled for overall time trends. Fourth, we used stacked cross-sectional data, and thus, we cannot assume causality in interpreting our results. Unobserved individual- or community-level variations such as the regional variation in prices of beverages might have affected the relationship of the individual-level associations with beverage consumption patterns.

SSBs have been reported as one of the key dietary contributors to increased obesity prevalence [45–47]. SSBs, particularly soda, have been at the center of the debate related to obesity control with recent efforts to enact fiscal pricing instruments such as excise taxes on SSBs in the United States and other developed countries [35–37]. South Korea has experienced rapid westernization in overall dietary patterns towards less plant food consumption, more animal food and dietary fat consumption [33, 38] despite that some of the traditional dietary patterns have also been retained [31, 35, 36]. SSBs have not yet been a focus in South Korea regarding obesity control unlike in the U.S. [6, 31]. However, this is likely to change given the rapid increase in the prevalence of overweight people in Korea, particularly among children and adolescents [48], and the extant literature reporting the potential negative impact of SSBs on body weight [45] and other related chronic diseases [14–17, 19].

Given the high attention to SSBs with regards to obesity control, it is important to assess the nature of SSB consumption in terms of not only time trends but also individual-level associations with the odds of consumption and caloric intake from SSBs in a global perspective. Building on the previous literature, this present study focused on beverage consumption and individual-level association patterns in South Korea. We provided important global evidence on the increase in SSB consumption, particularly for fruit drinks and miscellaneous SSBs. This suggests that South Korea is following the global nutritional transition toward greater consumption of sugars [30, 49]. In addition, although our results revealed that higher-SES individuals were more likely to consume SSBs, we found significant but small differences in the extent of caloric intake from SSBs across individual-level SES. Thus, our findings imply that there is a need for policies focusing on all segments of the population to support healthy beverage consumption in South Korea.

South Korea is following the global nutrition transition toward greater consumption of SSBs. However, the prevalence of SSB consumption was higher among high SES-people unlike other developed countries. Future studies should continue to explore broad international evidence for the determinants of SSB consumption to develop effective policy measures that can minimize any preventable societal costs stemming from the transition and consequential health impacts.