Nowadays, fitness, i.e. having an ideal weight and appearance, seems to be very important among young adults (
1). Fitness is considered an important part of one’s identity, which immediately appears in social situations when one is in the presence of others (
2). Fitness and beauty are representative of many things, such as social base, especially for women; people use positive features to describe attractive persons, while this is not the case with regard to unappealing persons (
3). Conceptual belief of weight and fitness has become one of the major criteria of beauty, especially among females (
4). It seems more important to teenagers, who face a set of behavioral changes due to their biological, social, and mental growth, including a tendency towards independence, searching for patterns out of family, and their need to be approved by others (
5). Therefore, a young woman may create a sense of displeasure with her body if she is not satisfied with her fitness, which results in nutrition disorder patterns (
6-
8). It could eventually lead to physical problems (like malnutrition, obesity, overweight, osteoporosis, and a higher rate of mortality) and mental consequences (like lower self-esteem, depression, and anxiety) (
9,
10). An eating disorder is a syndrome where one’s perception of food, body weight, and nutrition patterns leads to potentially life-threatening nutritional and medical complications (
11). Eating disorders are the most common type of disorders among teenagers after obesity and asthma (
4). Studies in the field in other countries have reported the prevalence of eating disorders to be 1% to 10.9% (
12); in the Islamic Republic of Iran, it has been reported to be from 6.3% to 9% (
13,
14). Eating disorders can start as mild forms of disorders in nutrition attitudes and abnormal attitudes to eating, including abnormal attitudes to current and ideal weight, conception of body and eating behavior, and preoccupations with food, its metabolism in the body, and its excretion (
15). But later, they can turn into severe clinical and almost irreversible forms like nervous anorexia and overeating, therefore identifying those at risk in this age group is important (
16). The prevalence of abnormal eating attitudes in the Islamic Republic of Iran is 16.7% overall (
16), while among people with normal weight 11.1%, the obese 16.7%, and the very obese 31.8% (
17). Considering the importance of the issue, it seems necessary to conduct preventive interventions. Studies have shown that a focus on mediator and predictive behaviors is essential in comprehensive health education and promotion programs (
18-
22). In this regard, the theory of planned behavior (TPB) is one of the most theories; it has been applied for prediction of behavior. TPB was offered by Icek Ajzen. According to TPB, the primary determinant of behavior is one’s intention to engage in a certain type of behavior. In addition, intention is predicted by three constructs: (a) attitudes, (b) subjective norms (SN), and (c) perceived behavioral control (PBC). TPB has been applied in studies to link beliefs and behavior in several fields including health-related behavior (
23). Fitness and its relationship with eating disorders among young adults, many studies have mentioned the role of considered factors in TPB (
24-
27). Furthermore, several studies have shown the usefulness of TPB in predicting health behaviors (
28-
31).