This study analyzed the secondary data of 3,641 adults aged 19 or older in data from the 2018 National Health and Nutrition Examination Survey in Korea and investigated the effect of eating alone on depression in each group classified by income level.
Among the subjects in this study, 28.3% did not eat with others, which was higher than 14.6% in the study by Takako in Japan [28]. This might be due to different definitions of eating alone. In this study, eating with others more than twice a day was defined as a companion meal, and in Takako 's study, eating with others more than two days a week was defined as a companion meal. There are many studies on companion meals, but there is no generalized companion meal evaluation method yet, and direct comparison is difficult because it is measured heterogeneously. However, unlike in the West where individualism is prevalent, it is very meaningful to continue research on groups that eat alone in the East where collectivism is a custom.
Eating alone is reflected in undernourished meals, short mealtimes, and social isolation and is likely to lead to unbalanced nutrition, as well as adverse mental health effects. Also, if you don't have social interaction, you feel depressed [35]. However, it is unreasonable to regard a companion meal as an unconditional "good deed" if one feels pressured and affected by the mood of the companion they are eating with [36].
The depression rate of the Korean adult subjects in this study was 15.6%. In Son's study [21], the Korean adult depression rate was 12.6%, and in Takako's study in Japan [28], the Japanese adult depression rate was 32.8%, which was different from the results of this study. A direct comparison of the rates is difficult because the tools for screening for depression were different. There are various tools for screening depression, such as the Beck Depression Inventory (BDI) and Center for Epidemiological Studies-Depression Scale (CES-D), and prevalence is widely reported according to the diagnostic tool used.
In the case of the Korea National Health and Nutrition Examination Survey, the tool for screening depression was PHQ-9, and out of a total of 27 points, the cutoff point for depression was 5 points. However, various results have been reported depending on whether or not the cutoff point was 10 points [34]. Depression has gradually increased with time, indicating that the problem of depression is becoming more serious.
This study investigated whether or not eating with others was related to depression in the low-income group. Depression was significantly higher in the group that did not eat with others. Previous studies reported that the more people did not eat with others, the higher the perception of depression, suicidal thoughts, and stress [16]. Wang's study also confirmed that eating alone affected depression [26]. It is difficult to compare the results directly to those of Kim and Son because the tools for screening for depression were different [16, 21], but the relationship between eating alone and depression was the same.
It is believed that spending time with family, friends, and colleagues while eating relieves depressed moods and has social support effects, which helps to reduce depression. Companion meals and the income levels of the subjects in this study were significantly correlated, and the proportion of companion meals in the high-income group was higher than that of companion meals in the low-income group. In Park's study [22], the proportion of people in the low-income group who did not eat with others accounted for the highest at 31%, and the scope review study confirmed that socioeconomic levels were related to companion meals [37]. It is thought that the higher the income level, the more social and economic resources are available, so there is no burden on establishing social relationships at a meal table and there is time to do so. In contrast, in the low-income group, the rate of eating with others or conducting social exchanges was low because there were no economic resources or time available. In addition, as shown in Jo's study that the low-income ratio of single-person households was about four times higher than the low-income ratio of multi-person households [38], this study also estimated that people in single-person households did not eat with their families.
Lifestyle and health levels vary depending on the income level, and income levels are known to be major factors that affect mental health and chronic diseases such as high blood pressure, diabetes, depression, and suicidal thoughts. Previous studies reported that income levels affected depression [6]. Thus, based on the hypothesis that income levels regulate the influence of whether eating or not eating with others affects depression, this study used income levels as a moderating variable. This is also meaningful in the direction of expanding the review of companion meals in the future.
When the control variable was viewed as the income level and the group was divided, there was also a difference in the effect of eating alone on depression. Regression analysis performed after controlling for general characteristics, health behavior characteristics, and health-related characteristics showed that depression was 1.4-times higher in those eating alone compared to those eating with others. The effect of low-income levels on depression was considered to be associated with low-priced convenience foods or lunch boxes at convenience stores, or involuntary motives for not eating with others rather than voluntary reasons. In addition, eating alone may be inevitable due to poverty’s effects on social relationships.
In contrast, in the high-income group, whether or not people ate with others did not significantly affect depression. It is assumed that when the income level is high, people eat regularly and eat high-quality healthy food, and the motivation for eating alone tends to be spontaneous. And the motivation or purpose of eating alone is clear and the satisfaction with eating alone is high, so eating alone did not affect depression.
As a limitation of this study, since there were no items to evaluate social relationships or social support in the raw data, not all of the various factors affecting depression were identified. Therefore, it is necessary to clearly understand differences according to each situation through additional research and accurately understand the factors affecting depression.
Nevertheless, the strength of this study was that most of the studies related to eating alone were analyzed for different age groups. This study is meaningful in that it is the result of stratifying and analyzing adult subjects according to income levels. In addition, it is meaningful that the association between eating alone and depression was not simply generalized, but other indicators affecting depression by income level were presented.
From the results of this study, since eating alone affected depression in the low-income group, policy alternatives such as cultural education on eating habits and securing public spaces are needed to prevent depression in the low-income group. Furthermore, payments for projects or vouchers that provide high-quality food for low-income families can also be a basis for preventing depression. In the low-income group, where eating alone affected depression, when assessing or intervening, it is necessary to identify companion meals and improve the dietary environment, and in the high-income group, where eating alone did not affect depression, other factors should be considered. In other words, it is meaningful that risk factors were identified according to income level and can be used as a reference in depression assessment and intervention.