In today's society, the aesthetic trend of thinness is also popular all over the world, and weight loss had become a more popular topic. The method of losing weight by controlling food intake was also relatively common in China (Lou, 2015). Restricted eating refers to individuals who strictly control food intake over a long period of time in order to lose weight or maintain body shape (Heman, 1975). Restricted eating has the following characteristics: (1) Long-term restrictive food intake with the goal of weight control or weight loss (Van strien, 1997; Papies, Stroebe et al, 2008; Johnson, Pratt, & Wardle, 2011); (2) Long-term and sustained efforts to limit eating urges and eating behaviors (Kong et al., 2011); (3) Eating behavior is easily influenced by external cognitive cues and information, while internal physiological signals (such as hunger or satiety) are relatively ignored (Hibscher & Herman, 1977; Polivy, 1985); (4) Young women are high-risk groups (Kong et al., 2011). During the development of diet-related mental illnesses, restricted eating greatly increased the probability of binge eating disorder, bulimia, and obesity in the future, which was the key point for shifting from unhealthy eating psychology to unhealthy eating behaviors (Schaumberg et al., 2016). In recent years, the population of eating disorders in China had grown rapidly in recent years, and the high incidence of restricted eating has became younger and younger, among which female college students were the most prominent (Kong et al., 2011). Therefore, research on restricted eating in college students not only helps to explore the influencing foctors of eating disorders, but also further enlightening us on how to prevent and treat eating disorders.
1.1. Social networking sites use and restricted eating
Social networking sites are social networking platforms based on the network. Users can set up their own home pages on the platform, browse and release information, and communicate with other users (Boyd & Ellison, 2007). In China, the most popular social networking sites are WeChat, QQ, Weibo, etc, they could be called China's Facebook, Twitter, instagram. Using social networking sites are becoming part of one's life, and contemporary social networking sites are filled with images, videos and texts about ideal bodies and perfect appearance. For example, a content analysis of advertisements on teen websites found that the majority of characters in the advertisements were female, young, and thin (Grabe et al., 2008).
According to sociocultural theory, social culture greatly affect individuals' self-perception and evaluation. Internalization is the main way for individuals to respond to social culture, which mean that individuals take the requirements and concept in social culture as their own behavior standards. In addition, according to social comparison theory (SCT) (Festinger, 1954), individuals often know themselves by comparing with others in the society, which plays an important role in the formation and development of individual self-concept. Social networking sites as one of the most important places for individual social comparison (Perloff, 2014; Lee, 2014) also served as mass media to produced and spreaded social culture (Yi & Wang, 2017). However, the image of ideal body and perfect appearance was wildly created and promoted on contemporary social networking sites (Holland & Tiggemann, 2016). This allowed individuals to spontaneously internalize their aesthetic standards of being thin as beauty, and compared them with the ideal image on social networking sites, which in turn led to dissatisfaction with the individual's body (Fioravanti, 2022), wanted to be "thinner" and "beautiful", resulted in restrictive eating behaviors (Holland & Tiggemann, 2016; Tiggemann & Slater, 2014). Therefore, this study proposed hypothesis 1: Social networking sites use could positively predict restricted eating.
1.2. The mediating role of appearance perfectionism
Appearance perfectionism means that individuals set unrealistic high requirements on the appearance of themselves or others, insist on this standard and measure their value on whether they achieve the perfect appearance (Yang, 2007). It was generally divided into two dimensions: hope for perfect appearance and worry about appearance imperfection.
According to sociocultural theory, the ideal image promote by social networking sites would cause individuals to internalize an unrealistic perfect image and pursued an appearance that is respected and praised by a social culture in order to gain social recognition, while appearance perfectionism produce or aggravate. According to social comparison theory, social networking sites are filled with a large number of ideal images, which will lead individual to make upward social comparison in appearances, deepen the appearance pressure and physical dissatisfaction they felt, pursued appearance perfection, and adopt restrictive eating behaviors. Viewed ideal images on social networking sites triggered individual appearance-based social comparisons, and the direction of this social comparison was largely upward (Holland & Tiggemann, 2016), which would have a negative impact on individual psychology, such as worse Body image, anxiety, appearance stress, over-internalization, etc. (Fardouly & Vartanian, 2015). Meanwhile, some studies had directly confirmed that exposured to ideal images on social networking sites increased body dissatisfaction in young women (Fardouly & Holland, 2018). Body dissatisfaction and appearance stress were highly correlated with appearance perfectionism (Wade & Tiggemann, 2013; Leng et al., 2020). According to the above theory and research, it could be concluded that the use of social networking sites would affect the degree of individual's appearance perfectionism.
According to transdiagnostic theory of eating disorders (Fairburn et al., 2003), appearance perfectionists set a extremely strict expectations for their own appearance, and these expectations were accompanied by harsh self-evaluation, which could lead to restricted eating and other weight-control behaviors. Some studies confirmed that restrictive eaters were accustomed to all-or-nothing thinking (MacNeil & Leung, 2022; Schmidt & Treasure, 2006; Shafran et al., 2002), that was also characteristic of perfectionists (Pacht, 1984). Young women with neurotic eating disorder had higher tendency to perfectionism (Chen ,Wen, & Chen, 2012; Wade, Gillespie, & Martin, 2007). Stoeber and Yang (2015) found that appearance perfectionism could explain 9–17% of the variation in eating disorders. Appearance perfectionism could worsen an individual's negative body image (Yang et al., 2017), the constant monitoring and dissatisfaction with appearance made individuals paid more attention to and worried about their body shape and appearance, which may induce more unhealthy eating behaviors, such as restricted eating (Brechan & Kvalem, 2015). Therefore, we proposed hypothesis 2: Appearance perfectionism mediates the relationship between social networking sites use and restricted eating.
1.3. The moderating effect of self-focus
Self-focus referred to individuals pay more attention to various aspects of themselves than to the external environment and things (Green et al., 2003), it contained four dimensions: social physiological perception, individual physiological perception, individual psychological perception, social psychological perception (Kiropoulos & Klimidis, 2006).
According to the cognitive resource theory (Kahneman, 1973), individual cognitive resources were limited. If an appearance perfectionist increased his attention to his own physical activities and body movements, he would decrease his attention to his external environment, thereby reduced the internalization of social idealization standards, improved the sensitivity and accuracy of their own physiological signal awareness, and reduced restrictive eating behaviors. According to the self-focus model proposed by Carver and Scheier (1981), when an individual perceived that the possibility of his own success was low, he was more likely to stop his efforts and given up his goal than low degree of self-focus, because high levels of self-focus also increased the individual's focus on potential personal failure. This suggested that a high level of self-focus might make individuals more likely to perceive that the goal of perfect appearance was unattainable in the pursuit of unrealistic perfection, thereby made it easier to abandon the pursuit of ideal appearance, reduced restricted eating behavior. Therefore, we proposed hypothesis 3: Self-focus moderates between appearance perfectionism and restricted eating.
To sum up, based on sociocultural theory and social comparison theory, this study proposed a model including four variables: Social networking sites use, restricted eating, appearance perfectionism, and self-focus. The purpose of this study was to studied the relationship between social networking sites use and restricted eating, and the mediating role of appearance perfectionism and the moderating role of self-focus (as shown in Figure l).