Associations between dietary patterns and screen time among Korean adolescents

Rapid economic growth of Korea has changed people's lifestyle; in particular, the diet has become westernized [1] and sedentary time has increased [2]. Currently, a common sedentary behavior among children and adolescents is partaking in screen time, which includes time spent watching TV, using a computer, or playing DVD/video games. The American Academy of Pediatrics recommends that children and adolescents should limit the time for watching TV to 2 hours per day [3], but only 27% of them meet this recommendation [4]. Screen time is reportedly associated with dietary habits. In children and adolescents, longer screen time is positively associated with a higher intake of energy-dense foods such as high-fat foods, sugary snacks, or soft drinks [5-7] and inversely associated with the consumption of healthy foods such as vegetables and fruits [6]. Previous studies have reported data on the association between screen time and dietary patterns. A study including a French population showed that time spent watching TV is inversely associated with an unhealthy dietary pattern, which reflects a high consumption of alcohol and meat or convenience foods [8]. Another study among Spanish children and adolescents showed that more than 2 hours of TV-watching is likely to be associated with the dietary pattern of a high consumption of sweets, salted snacks, bakery products, and soft drinks [9]. On the contrary, a healthy dietary pattern such as the Mediterranean dietary pattern was found to be inversely associated with screen time among European children [10]. However, there is limited information on the association between dietary patterns and screen time in Asian populations.

It was reported that the penetration rate of internet access in the South Korea population has reached almost 100%, which is the highest level worldwide [11]. Thus, we propose our hypothesis on the association between diet and screen time: more Korean adolescents are exposed to high screen time compared with those in other countries and they have thus developed unhealthy dietary patterns. To our knowledge, no study has been conducted on the association between dietary patterns and screen time among Korean adolescents; thus, the present study was aimed to derive dietary patterns and analyze such association using data from the Korean National Health and Nutrition Examination Survey (KNHANES).

Using the 2005 KNHANES data, we identified 2 major dietary patterns Korean healthy dietary pattern and the Western diet and fast foods pattern among Korean adolescents aged 13-18 years. Furthermore, we observed that the Korean healthy dietary pattern was inversely associated and the Western diet and fast foods pattern was positively associated with screen time.

The Western diet and fast foods pattern determined in this study is similar to those reported in previous studies [1, 15]. Kim et al. [1] identified 3 types of dietary patterns among Korean adolescents aged 10-19 years: the Korean traditional pattern characterized by a high consumption of rice, kimchi, legumes, fish, and seaweed; the Western pattern characterized by a high consumption of flour, bread, hamburgers, pizza, cereals, snacks, sweets, sugar, meats, and beverages, and the modified pattern characterized by a high consumption of noodles, dumplings, rice, and kimchi. Song Y et al. [15] also identified 3 types of dietary patterns: the traditional pattern, which is contributed to by rice, kimchi, fish and vegetables, the Western pattern, which is contributed to by flour, bread, hamburgers, pizza, meat, meat products, dairy products and soft drinks, and the traditional dietary pattern, which is contributed to by noodles and dumplings. Some data are also available on the dietary patterns in adolescents with different ethnicities. The Western style diet and the healthy dietary pattern were identified among Australian adolescents, and the healthy dietary pattern was characterized by a high consumption of whole grains, fruit, vegetables, fish and legumes [16]. Among Brazilian adolescents, the Western style dietary pattern, the traditional dietary pattern, and the mixed dietary pattern were prevalent, and their traditional dietary pattern was shown to be high in the consumption of rice, bread, milk, and beans [17]. Among Spanish adolescents, the Western style dietary pattern and the Mediterranean dietary pattern were identified, and the Mediterranean diet was characterized by the high consumption of dairy products, fish and seafood, eggs, legumes, fruit and vegetables, and olive oil [10]. In comparison to these patterns, the Western style dietary pattern was similar to that observed among Korean adolescents although their traditional diet or healthy dietary patterns were unique. In Korea, a typical Western style diet has become one of the most common dietary patterns among adolescents as well as among adults, and Western foods are more widely available now than they were 30 years ago. Because it is known that the Western style diet is related to an increased risk of coronary heart disease, type 2 diabetes mellitus, colon cancer, obesity, hypertension, and autoimmune disease [18, 19, 20], Koreans are more likely to be at risk of these chronic diseases. Among adolescents in particular, the Western dietary pattern is reportedly associated with attention-deficit hyperactivity disorder [21] and metabolic syndrome [22]. Since diets in childhood and adolescence affect health as well as eating habits in adulthood, the establishment of a healthy dietary pattern in the early stage of life is critical for the prevention of chronic diseases.

Several studies have examined the association between dietary patterns and screen time. Among French adults, an unhealthy dietary pattern, which reflects a high consumption of alcohol and meat or convenience foods, was inversely associated with time spent watching TV [8]. Among Spanish children and adolescents who spend more than 2 hours a day watching TV, a high consumption of salted snacks, sweets, bakery products, and soft drinks was observed [9]. On the contrary, a healthy dietary pattern such as the Mediterranean dietary pattern was found to be inversely associated with screen time [10]. However, data on the association between dietary patterns and screen time have not been reported for Koreans or other Asian populations. In present study, we observed a significant association between the Western diet and fast foods pattern and screen time. In particular, handheld foods, such as convenience foods, fast foods, and bakery products or snacks, appeared to contribute to the Western diet and fast foods pattern that we identified. On the basis of these findings, we postulate that Korean adolescents with excessive screen time consume increased amounts of handheld foods, with which a person is able to continuously watch TV or view computer screen. A typical Korean meal includes more than 3 dishes (rice, soup, and side dishes) and all dishes are served on a table at the same time; thus, a person should have a formal table setting for a typical Korean meal. This may support our finding that adolescents with excessive screen time were less likely to have the Korean healthy dietary pattern.

The strengths of our study include the use of national data and the analysis of dietary patterns; importantly, this is the first report on the association between diet and screen time among Korean adolescents. In particular, the analysis of dietary patterns provides information of overall dietary habits in real life, whereas that of nutrients or specific food items does not provide any such information. The present study had a few limitations too. First, because of a cross-sectional design, a causal relation between dietary patterns and screen time was undetermined. Thus, a prospective study is warranted to clarify this relation. Second, we were unable to estimate actual amounts of food items consumed because we used the dietary information from the FFQ, which includes only the consumption frequencies of food items. We performed a factor analysis using 24-hour dietary recall data, but we were unable to identify notable dietary patterns using only 1 day's diet information.

On the basis of our findings, we conclude that excessive screen time may affect not only dietary habits but also nutritional status, growth, and health in Korean adolescents. We suggest that a guideline specifying an acceptable screen time for Korean adolescents is needed, and nutritional education for those spending excessive screen time should be emphasized in schools.