Effects of eating dinner alone on overweight in Japanese adolescents: a cross-sectional survey

Childhood obesity is one of the most serious public health challenges of the twenty-first century [1], and the increase in obesity is possibly associated with inappropriate dietary habits [2]. Previously published studies report that eating family meals together is a potential factor that may protect against unhealthy eating and obesity during childhood and adolescence [3‐9]. Increasing the frequency of eating family meals together may decrease the risk of overweight or obese in children and adolescents [8]. A meta-analysis suggested that children and adolescents in families that share ≥3 family meals/week are 12% less likely to be overweight in comparison with those who share < 3 family meals/week [4]. A previous study reported that eating meals as a family every day is associated with a lower rate of obesity, as well as good lifestyle habits such as eating balanced meals [5]. Thus, the family meal is important for preventing overweight and obesity in children and adolescents.

However, a recent study showed a decrease in the frequency of family meals among Asian youth between 1999 and 2010 [10]. In Japan, Adachi reported that 12.6% of children eat their breakfast with all members of their family, and this is a 10% decrease compared with a similar study that was conducted approximately 20 years ago (in 1981) [11, 12]. In addition, Adachi reported that 26.4% of children eat breakfast alone, 24.5% eat with other children but no adults, and these two groups combined showed a 12% increase compared with results reported 20 years ago [11, 12]. Moreover, the increase in the proportion of children eating alone is often lamented in the popular media in Japan [13].

Previous studies reported that adolescents who eat breakfast alone tend to have a low intake of vegetables and fish in their daily diet, thereby suggesting unhealthy dietary habits [14, 15]. Therefore, adolescents who eat breakfast alone might have an unhealthy diet, which increases the risk of overweight or obese. However, to the best of our knowledge, there are few studies on the relationship between eating dinner alone and being overweight in Japanese adolescents [16, 17].

Accordingly, here we investigated if eating dinner alone is associated with being overweight in Japanese adolescents of each sex. Our hypothesis was that a high frequency of eating dinner alone would be associated with being overweight in adolescent boys and girls.

Among the 890 participants, 5 participants refused to participate in the program (participation rate = 99.4%) and 5 participants were excluded because of incomplete data. Therefore, a total of 880 participants (470 boys and 410 girls) were analyzed in the present study.

The characteristics of the study participants (boys and girls) are shown in Table 1. The proportion of overweight boys was significantly higher than among girls. Although the proportion of participants who ate dinner alone was 14.7% among boys (6.0% and 8.7% reported eating alone ≥3 times/week and 1–2 times/week, respectively) and 10.8% among girls (4.9% and 5.9% reported eating alone ≥3 times/week and 1–2 times/week, respectively), the difference in the proportions between boys and girls did not reach a significant level. Moreover, statistically significant differences between boys and girls were observed in terms of maternal employment, sports teams’ participation, dinner time, eating speed, and eating until full.

The characteristics of the overweight and the non-overweight participants by sex are shown in Table 2. Statistically significant differences between the overweight and the non-overweight participants were observed in terms of the eating speed for each sex. The proportion of participants who ate fast was higher in the overweight group than in the non-overweight group regardless of sex. Among boys, the proportion of participants who were only children was higher in the overweight group than in the non-overweight group. A statistically significant difference was not observed in terms of eating dinner alone between overweight and non-overweight boys. In contrast, a statistically significant difference between the overweight group and the non-overweight group was found among the female participants who ate dinner alone; the proportion of participants who ate dinner alone in the overweight group was higher than in the non-overweight group.

Next, the crude and adjusted ORs of eating dinner alone for the overweight participants were calculated for each sex, as shown in Table 3. When compared with girls who did not eat dinner alone, a significantly increased OR was observed among the girls who ate dinner alone ≥1 time/week (adjusted OR = 2.78; 95% CI = 1.21–6.38). In contrast, there was no statistically significant difference between eating dinner alone and being overweight among boys.

The present study shows that the proportions of children who eat dinner alone ≥3 times/week were 6.0% among boys and 4.9% among girls. According to a survey of schoolchildren in Japan (performed in 2010), 6.0% of junior high school children eat dinner alone ≥3 times/week, which is similar to the results of our study [24]. Eating alone is believed to lead to unhealthy dietary habits because such adolescents are not supervised by their guardians and consequently often eat only the foods they like [15]. Therefore, it is important to consider eating alone as a serious health problem among children and adolescents.

In this study, eating dinner alone was significantly associated with being overweight among girls. One explanation for this result is that eating dinner alone might lead to unhealthy dietary habits, thereby resulting in being overweight. Previous studies have reported that family meal times may act as a protective factor against many nutritional health-related problems encountered during childhood and adolescence, including issues related to being overweight, unhealthy eating, and disordered eating [4, 8]. In addition, Feldman et al. reported that families who choose to eat together might be more likely to try to prepare well-balanced, nutritious meals in comparison with adolescents who eat on their own and may rely on prepackaged convenience foods for meals, which often lack fruits and vegetables [25]. Therefore, our study findings suggest that eating dinner alone leads to adolescents being overweight.

Furthermore, in the present study, we report the sex differences among adolescents in terms of the association between eating dinner alone and being overweight: compared with girls who did not eat dinner alone, those who ate dinner alone ≥1 time/week were at a greater risk of being overweight, but there was no statistically significant relationship between eating dinner alone and being overweight among boys. These results remained even after propensity score adjustment. A previous study reported that, among girls, the intake of food items such as fish and vegetables significantly differed between those who always ate dinner with their family and those who rarely ate dinner with their family, but among boys there was no significant difference in food intake depending on family eating habits [26]. Neumark-Sztainer et al. suggested that regular family meals during adolescence plays a protective role against extreme weight control behaviors and disordered eating behaviors in adolescent girls, but not boys [27]. Moreover, boys’ mothers tend to prepare meals for their sons, and girls’ mothers usually encourage their daughters to cook for themselves [26]. Therefore, when adolescent boys and girls eat dinner alone, boys might eat meals prepared by their mothers, whereas girls might freely cook their favorite menu items, thereby resulting in an unhealthy diet and eating behaviors. In this study, the proportion of participants who eat until full, which has been reported to be associated with being overweight [28], was significantly higher among girls who eat dinner alone (50% and 55.0% of girls eat until full among girls who eat dinner alone 1–2 times/week and ≥3 times/week, respectively) than in girls who do not eat dinner alone (33.6% of girls who do not eat dinner alone also eat until they are full) (P = 0.048; data not shown). Therefore, it could be important to reduce the frequency of eating dinner alone in order to promote healthy eating behaviors and prevent overweight status among adolescents, especially girls.

The present study also has some limitations. First, the questionnaire used in our study was not validated. Therefore, to verify our study results, a validated questionnaire should be used in future research. Second, this study did not consider factors in the home environment such as watching television during meals [8, 25]. For example, watching television during family meals is associated with poorer dietary quality among adolescents [25]. Therefore, these factors could have affected our study findings. Third, the participants in this study were seventh graders (12–13 years of age) from a single town in Japan, which might limit generalizability to other countries. Finally, the present study could not determine a causal relationship between eating dinner alone and being overweight because it was a cross-sectional study. Therefore, the possibility of reverse causality cannot be denied.

The present study found that eating dinner alone is significantly associated with being overweight among adolescent girls, but there was no statistically significant relationship between eating dinner alone and being overweight among adolescent boys in this community in Japan. Therefore, reducing the frequency of eating dinner alone might contribute to decreasing the risk for being overweight or obese among adolescent girls.