School lunches play an essential role in improving the students' nutritional status, learning capacity, and school attendance [1]. As of 2012, school lunches were provided to approximately 368 million students on a typical school day worldwide, covering most countries around the world [2]. 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.

In China, home lunches have remained a big part of all lunches consumed by elementary and secondary school students. Students attending schools not serving school lunches return to schools after eating lunches at home. A survey conducted in six major cities in China in 2009 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 12~17-year-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 lunches has remained an understudied area in China. In particular, there are no reports on a comparison of the dietary quality between school lunches and home lunches in China. This study examined the dietary quality of school lunches in China using the 2011 China Health and Nutrition Survey, with a focus on comparing school lunches with home lunches.

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.

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.

Unbalanced meal composition may cause nutrition problems. Although there has been considerable improvement in the daily diets accompanied by China's significant economic development, the inadequate intake of several nutrients still remains as problems. According to several empirical studies in China, deficiency of several nutrients, such as calcium, iron, and vitamin D, was related to the inadequate intake of fruits, vegetables, and dairy products [36, 37]. The results of the present study revealed similar problems of an unbalanced food group intake from both school and home lunches.

In 1998, the Ministry of Health in China established a standard suggesting school lunches to provide 40% of the Dietary Reference Intakes (DRIs) and presented nutrient-based and food-group based amounts for school lunches [26]. On the other hand, these standards only served as guidelines for foodservice personnel rather than being compulsory and enforced by the government [38]. This may partially explain the inconsistency in the quality of school lunches in China. The standard was revised in 2017 and renamed as Nutrition Guidelines of School Meals [9].

Japan and South Korea, China's neighboring countries, enacted the School Meals Act and legislated nutritional standards [39]. Both countries implemented nutrient-based standards that were revised periodically to be consistent with the reference values of the DRIs. It seems to be essential for China to make the nutritional standards for school lunches compulsory in school lunch services to reduce the nutritional quality gap among them.

This study focused on the analysis of students' reported food intake from both school and home lunches. The actual food intake is generally influenced by the dietary guidance by parents or school food service personnel and provision of school lunches, as well as the students' personal preference. The results of this study showed that both school and home lunches lacked dietary diversity. On the other hand, some elementary school lunches provided foods from an even smaller number of food groups than home lunches. Several studies revealed similar problems [7, 11, 40], but an inferior quality of school lunches in some schools compared to home lunches was not reported before this study.

Previous studies showed that parents could positively influence children's food choices when dining together at home [41, 42]. The result of the current study showed students in the home lunch group consumed a wider variety of vegetables than those in the school lunch group, which may reflect the parents' positive influence at home [43]. Most schools in China currently do not have dietitians [44], which may have resulted in the absence of this kind of dietary guidance at schools. Countries, such as South Korea and Japan, have redefined the roles and responsibilities of school dietitians. For example, South Korea adopted the Nutrition Teacher System in 2006 and had nutrition teachers replace school dietitians. Nutrition teachers play dual roles as teachers on nutrition as well as managers of school food operations [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.

The dietary quality of Chinese students' lunch consumed at schools did not appear to be superior to that of the students' lunch consumed at home in general. To improve the quality of school lunches in China, the balance and diversity of the menu composition should be considered. In particular, school lunch menus should be planned to reduce the amount of meats, increase the amount of vegetables, and include dairy products and fruits. In addition, it would be helpful to consider adopting compulsory nutritional standards and employing dietitians, whose main roles are to manage school lunch services. The school lunch service in China has much room to improve compared to school lunches in other advanced countries. The efforts in revising school meals in China will become a driving force for improving the nutrition and health of children and adolescents in the future.