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Dietary Quality Comparison of the School and Home Lunches Consumed by Chinese School-Age Children and Adolescents: Analysis of the 2011 China Health and Nutrition Survey

Acknowledgments This research uses data from China Health and Nutrition Survey (CHNS). We are grateful to research grant funding from the National Institute for Health (NIH), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) for R01 HD30880, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) for R01DK104371 and R01HL108427, the NIH Fogarty grant D43 TW009077 for financial support for the CHNS data collection and analysis files since 1989, and the China-Japan Friendship Hospital, Ministry of Health for support for CHNS 2009, Chinese National Human Genome Center at Shanghai since 2009, and Beijing Municipal Center for Disease Prevention and Control since 2011. We thank the National Institute for Nutrition and Health, China Center for Disease Control and Prevention, Beijing Municipal Center for Disease Control and Prevention, and the Chinese National Human Genome Center at Shanghai.

In China, the school lunch service was first launched in a few coastal cities in the 1980s [3]. The school lunch service was expanded and covered 90% of large cities, 70% of middle and small-sized cities, and 20% of rural areas in 2010 [4]. Since 2011, the Chinese government has undertaken the Nutrition Improvement Program for Rural Compulsory Education Students, which focused on building new school cafeterias and providing school meal allowances in underdeveloped rural areas in China [5]. The aim of the Nutrition Improvement Program was to improve the nutritional status of rural students and to decrease the gap between urban and rural populations [6].
As the number of schools offering school lunches has increased in China, considerable attention has been paid to quality aspects such as menu composition and serving size.
Although school cafeterias provided seasonal menu items and periodically updated menus [7,8], unbalanced menu composition and a lack of food variety were revealed as the main problems [4]. The current nutrition guidelines of school lunches in China specified six food groups and their recommended amounts to be included in one meal for the respective age groups. The food groups are grains, fruits· vegetables, fish·meat·eggs, milk·soybeans·nuts, vegetable oil, and salt [9]. However, the majority of school lunches appeared to not having included recommended amount of foods. In general, school lunches in China offered too much meat [10][11][12], but not enough fruit, vegetables, or dairy products [11]. Among 9,346 elementary and middle schools in rural areas where the Nutrition Improvement Program was implemented, more than 70% of the schools offered vegetables and dairy products below the recommended amount [5].
Since the 1990s, the Chinese dietary pattern has experienced a drastic transformation from a traditional carbohydrate-rich diet into a westernized high-fat, low-carbohydrate diet [13]. The rate of obesity in Chinese students started to increase in the 1990s and has increased rapidly since the 2000s [14]. In 2010, approximately 10% of Chinese students were overweight, and 5% were obese, and the estimation represented 30 million in total [15]. At the same time, undernutrition among children and adolescents was another problem that China was facing.
The rates of stunting and wasting in China were approximately 3% and 9%, respectively. Moreover, the rates were as high as 25% (stunting) and 40% (wasting) in some poor areas in northwestern and southwestern China [16]. Therefore, the food environment needs to be changed to promote healthy food choices and prevent the further prevalence of youth obesity. Furthermore, it is equally important that sufficient nutrients be provided to children and adolescents in poor areas through healthy diets. showed that approximately 26% of 6~13-year-old students had lunches at home during the school year [17]. The 2015 National Report on Chinese Resident's Chronic Disease and Nutrition also showed that approximately 31% of 12~17year-old students had lunches at home [18]. In general, home food is relatively difficult to change in the short term because it reflects the food preference of the family and daily routine of family members. Therefore, improving the quality of school lunches can provide a more effective path to healthier dietary intake and dietary habits among students.
A recent study has shown that higher proportions of livestock and poultry meat and low intake of vegetables were integral problems in the school lunch programs in China [19]. In the study, the amount of livestock and poultry meat provided via school lunches was almost 5 to 8 times of the recommended amount. Another study reported that the average protein intake from school lunches by elementary school students reached 40% of estimated average requirement (EAR), while thiamine, riboflavin, vitamin C, calcium, selenium, and other nutrients were seriously inadequate [20].
Examining the quality of dietary intake from school

Data source and subjects
This study analyzed the data from the 2011 China Health and Nutrition Survey, which was conducted in nine provinces and three municipalities that varied substantially in geography, level of economic development, public resources, and health indicators. A multistage, random cluster process was used to draw the samples [21]. In the Survey, each participant has provided a written informed consent, and the study was approved by the institutional review boards at the University of North Carolina at Chapel Hill and the National Institute of Nutrition and Food Safety [21]. The current study used only the individual level dataset, and therefore was exempted for further IRB approval based on the guidelines for the data use of the China Health and Nutrition Survey [22].

Dietary quality measurements 1) Frequently consumed foods
Three hundred fifty-nine individual food codes were rearranged into 167 food codes by referring to the Chinese Food Composition Table 2002 and 2004 [23,24]. If one kind of food was reported in different food codes due to different cooking or processing methods, the food codes were combined into a single code. Four food codes (21199, 45419, 141999, and 152599) not existing in the Chinese Food Composition Table were excluded. The foods consumed frequently in lunches were ranked for the school lunches and the home lunches, respectively.

2) Amount of food group intake
All foods were classified into ten major food groups according to the Chinese Food Guide Pagoda in the 2016 Chinese Dietary Guidelines as follows [25]: grains/tubers/ legumes (excluding soybean), vegetables, fruits, meats, seafood, eggs, dairy products, soybean/nuts, salt, and oils.
Condiments such as sugar was not classified into any of these food groups. Soybean paste was the only sauce appeared in the 24 recall data of this study and classified into the soybean/nuts group. To determine if each food group intake was sufficient, the reported food group intakes except for salt and oils were compared with the reference values for school lunches (i.e., 40% of the recommended daily values for those whose energy requirement was 1600~2400 kcal) [26].

3) Food group intake pattern
Food group intake pattern was examined to evaluate the presence or absence of each food group at the lunch intakes. For the five food groups, including dairy products (excluding butter and cream products), meats (including meats, fish, eggs, legumes, and nuts and seeds), grains (excluding cake, cookies, pastries, and pies), fruits (including raw, dried, and canned fruits and fruit juices, but excluding fruit drinks), and vegetables (including raw, cooked, frozen, dried, and canned vegetables and vegetable juice) (DMGFV), number 0 and 1 indicated the absence and presence of the food group, respectively [27]. Soybean paste, the only sauce appeared in the data, was classified into meats.

477·Dietary quality of school and home lunches in China
The indicated number 1 means that a minimum amount or more of food belonging to the food group was consumed according to Kant' method [28]. To evaluate the presence or absence of each food group at the lunch intakes, onethird of the minimum amounts for each food group that was set in the Kant's study [28] were used. Therefore, in the meat, fruit, and vegetable groups, a minimum amount for indicating number 1 was 10 g for all solid foods with a single ingredient and 20 g for all liquids and mixed dishes.
In the dairy and grain groups, 5 g for all solid foods with a single ingredient and 10 g for all liquids and mixed dishes were set as the minimum amounts.

4) Dietary Diversity Score
Dietary Diversity Score (DDS) suggested by Kant [28] was calculated for the lunches consumed by students. For the same five food groups as used for the food group pattern analysis, one point was counted for each food group in which the consumption amount was at or more than the minimum amount. To calculate DDS for lunch intake, onethird of the minimum amounts for each food group that was set in the Kant's study [28] were used for point allocation.

5) Dietary Variety Score
The Dietary Variety Score (DVS) was calculated for the lunches consumed by students. The DVS indicated the number of food items consumed in a certain amount over a given period [29]. One additional point was added whenever a different food item was consumed.

Statistical Analysis
Statistical analysis was performed using the SAS (Ver. 9.4, SAS Institute Inc., Cary, NC, USA). The significance level was set to 0.05 for all analyses. The difference between the two lunch groups was analyzed by χ 2 test or ANCOVA using gender, household income, and residential area as covariates.

Sociodemographic characteristics of the study subjects
Among the 6~11-year-old students, 177 belonged to the school lunch group, and 457 belonged to the home lunch group. Among the 12~17-year-old students, 144 were classified into the school lunch group, and 306 were classified into the home lunch group. Approximately 27.9% of 6~11-year-old students and 32.0% of 12~17-year-old students ate school lunches. Table 1 lists the sociodemographic characteristics of the two lunch groups.
Significant differences were observed in the utilization of

Foods frequently consumed at lunches
Regardless of the age group, the most frequently consumed food in both the school lunch group and home lunch group was rice, followed by pork. Fruits and dairy products did not appear in the top 15 list of the frequently consumed foods in both lunch groups. The types of vegetables consumed in the school lunch group were less diverse than the ones consumed in the home lunch group in both age groups. In contrast, the types of meats consumed in the school lunch group were more diverse than those consumed in the school lunch group. Various kinds of meats, such as pork, chicken, and beef, appeared in school lunches, whereas pork appeared to be the only major type of meat in home lunches (Table 2). Table 3 shows the amount of lunch intakes for each food group. When 40% of the daily recommended intake in the Chinese Food Pagoda was taken as a reference, the over intake of meats and insufficient intake of seafood were observed in both lunch groups. The intakes of fruits and dairy products were almost zero. In terms of vegetable intake, both lunch groups among 6~11-year-old students consumed less than the recommended amount. However, the school lunch group (87.4 g) showed significantly lower consumption than the home lunch group (99.6 g) (P = 0.017). Among the 12~17-year-old students, the home lunch group (121.2 g) met the standard for vegetable intake, whereas the school lunch group (96.2 g) did not (P = 0.003). Table 4 shows the food group intake patterns of the school lunch and home lunch groups. The pattern found most frequently in both lunch groups was the one with meats, grains, and vegetables (DMGFV = 01101), which accounted for more than 70% in the school lunch group and more than 50% in the home lunch group in both age groups. Diets only composed of grains and vegetables (DMGFV = 00101) were 13.6% and 6.9% in the school

0.818
% or Mean ± SE 1) For meat, fruit, and vegetable groups, a minimum amount for allocating 1 point in Dietary Diversity Score is 10 g for all solid foods with a single ingredient and 20 g for all liquids and mixed dishes. For dairy and grain groups, 5 g for all solid foods with a single ingredient and 10 g for all liquids and mixed dishes are the minimum amounts. 2) By  2 test or ANCOVA with gender, household income and residential area as covariates 3) It is the value rounded to one decimal place. patterns showed significant differences in distribution between the school lunch and home lunch groups among 6~11 year-old students (P < 0.001) as well as 12~17 yearold students (P = 0.004). The results of Chinese students' overconsumption of meat and underconsumption of fruits and dairy products from school lunches seem to be due to the school lunch operations not following the nutritional guidelines of school meals. The overconsumption of meats from school lunches was because Chinese school lunches were generally composed of one meat dish and one meat-vegetable mixed dish [9]. According to an analysis of Chinese students' meat consumption during 1991~ 2011, the percentage of students who overconsumed meats increased from 32.9% in 1991 to 59.8% in 2011 [30]. Such a trend also reflects the increasing preference for low-carbohydrate, high-fat diets among students. As the proportion of students being either overweight or obese reached 15% in China [15], it is necessary to modify school lunch menus to decrease the amount of meats provided in school lunches.

Dietary diversity and variety of lunches
Since 2000, China has provided milk in elementary and middle schools [31]. Approximately 22.4 million students received milk at schools in 2014 [32], which accounted for about 10% of the total number of elementary and middle school students in China [33]. However, this number was not reflected in this study because the level of dairy product consumption was approximately zero. Milk might be provided at other times than lunch, but including milk in school lunches remains a high priority on the agenda for the school lunch program [34].
Adolescents' intake of fruits has increased continuously in China since 2010, but a study reported in 2016 showed that a half of the students still did not consume fruits daily [13].
Previous studies claimed that fruits were not provided as a part of school lunches in China [11,35], but the reason was not given. In China, meals are generally not accompanied by fruits, which may partially explain this problem.
Nevertheless, providing fruits at school lunches is needed to increase fruit consumption, as well as to raise awareness of the importance of eating fruits daily.  [45]. Japan also implemented a school-based nutrition education program and started the Nutrition Teacher System [46].
Compared to 6~11-year-old students, the advantage of home lunches was not observed in 12~17-year-old students.
The students at this age range developed personal preferences on taste. They tended to choose unhealthy foods due to a lack of nutrition knowledge [47]. Hence, improving nutrition knowledge could lead to a change in dietary behavior [48]. Nutrition education targeting students at this age range could play an important role in forming healthy dietary habits.
This study has several limitations. The data from the 2011 China Health and Nutrition Survey were collected mainly in fall and winter during a year. Therefore, the dietary intake data used in this study may be biased by seasonality and may not reflect the usual dietary intakes [30]. As this study only analyzed the food intakes rather than nutrient intakes, future research will be needed to analyze the nutrient intakes from both school lunches and home lunches.