Commensality, eating together, is a fundamental social activity of human beings throughout time and in every culture [1]. However, rapid social changes have significantly modified societal environments around eating together, and a decline in commensality has become a significant concern in modern societies. In conjunction with social changes in Korea, the dietary behavior of Koreans has also rapidly changed. The number of Korean people who eat alone has been increasing, and new terms related to eating alone have been coined, such as ‘honbabjok’ and ‘honbab’ [2].

Eating alone is a social concern that has emerged during a period of increased aging of the Korean population and increasing numbers of one-person households. The population of South Korea became an ‘aged society’ in 2018 and is expected to become a ‘super-aged society’ in 2026 [3]. The number of one-person households increased from 2.22 million (15.5% of the Korean population) in 2000 to 5.62 million (28.6% of the population) in 2017 [4]. One of 4 elderly Koreans aged 65 years old or above were reported to have eaten alone during the last year [5]; moreover, one-person households were more likely than multi-person households to eat alone [67]. Consequently, the number of ‘solo eaters’ is expected to increase in concert with the demographic changes.

Some previous studies reported associations of eating alone with various health problems. The effect of eating alone on depression or mental illness, especially in older adults, has been widely reported [78910], and eating alone is a direct risk factor for metabolic syndrome in middle-aged Koreans [1112]. Unhealthy dietary behaviors of solo eaters have also been reported. Eating alone has been correlated with a lowering of food intake [131415] and a high frequency of meal skipping [1617]. Significant close associations between eating alone and an insufficient nutrient intake or a low level of food diversity in different age groups have also been reported [8916171819].

Other studies have shown gender differences in eating alone behaviors. In one study, Korean women had lunch alone more often than men did, while men ate dinner alone more often than women did [20]. It was also reported that women ate significantly more and a greater variety of foods when eating together than when eating alone; however, men did not show such differences [21]. Moreover, Tani et al. [22] revealed that eating alone and living alone may be jointly associated with a higher prevalence of unhealthy eating behaviors in men but not in women. In middle-aged Korean adults, eating alone was associated significantly with a lower intake of potassium and calories from protein in men but not in women. In women, meal nutrient densities are reported to be higher when eating alone than when eating with others [19]. Dietary behaviors related to eating alone also differ by age, with young adults eating alone tending to consume simpler meals compared to those consumed by middle-aged adults when eating alone [23]. In addition, there are gender- and age-related differences in perceptions about eating alone. In men, eating alone was associated with negative perceptions such as loneliness or boredom. Conversely, eating alone in women was perceived as positive and associated with key words such as ‘free’, ‘joy’, and ‘my own time’ [20]. Also, compared to older adults, young adults reported feeling a greater level of convenience related to eating alone [23]. These various studies indicate there are gender and age differences in the nutritional intake of people who eat alone.

However, many previous studies have focused on nutrition intake and dietary quality differences between people who eat alone and those who eat together. There is an absence of detailed comparisons of dietary characteristics among the different types of solo eaters, and few studies have focused on gender- and age-related differences. Eating alone is not a phenomenon confined to a particular demographic group, such as one-person households. Since eating alone has become a typical diet pattern in busy modern societies, more in-depth studies are necessary. Accordingly, this study investigated gender and age group differences in dietary characteristics of solo eaters in order to obtain baseline data that will be useful in future research into improving the diet of solo eaters.

This study evaluated nutrient intake and dietary quality of people who eat alone and investigated the differences in those factors by gender and age. It has been shown that older adults and one-person households tend to eat alone [56], and the rate of eating alone in women is about twice that of men [5]. The same demographic characteristics of solo eaters were observed in our study. The energy intake of people eating alone was insufficient regardless of gender and age group, indicating that solo eaters do not consume as much as they need. Several other studies have also revealed that people eat less when they eat alone [131415]. A quantitatively deficient intake of energy could result in deficient intakes of nutrients, and our results showed low NARs for all nutrients in all of our subject groups. In particular, an excessively low intake of calcium and low calcium density of meals were common among people eating alone.

Besides the common dietary problems of solo eaters, peculiar differences by gender and age group were detected. Men consumed significantly higher amounts of energy and nutrients; consequently, their NARs were higher than women, except for vitamin C. However, the INQ of as many as 4 (calcium, vitamin A, vitamin C, and riboflavin) nutrients were below 1.0 in men, but only calcium was below 1.0 in women. This result suggested that men's diet was qualitatively poorer than that of women, which was also identified in their dietary patterns. Although men ate more menu items than women, their dietary diversity was quite the opposite. The food group intake pattern was relatively less ideal for men, and about 40% of men consumed neither fruit nor dairy products, resulting in a lower nutrient density of their meals. A previous study reported an association between eating alone and the risk of metabolic syndrome in middle-aged Korean men; however, no association was detected in women [19]. The nutrient density of women's meals was higher even when they ate alone [19]. Therefore, the qualitatively poor diet of men eating alone could be a risk factor for developing metabolic diseases.

Among the different age groups assessed, the middle-aged group showed relatively better nutrient intake and dietary quality compared to the other age groups. The middle-aged group intakes of calcium, iron, vitamin A, and vitamin C were the highest among the age groups, and their NARs were also higher than those of the other groups, resulting in the highest MAR and generally higher INQs. The relatively better diet quality of the middle-aged group was verified by the group having the highest DVS. This result could be explained by results in a previous study showing that adults in their fifties consumed relatively better prepared meals when eating alone compared to adults in their twenties or thirties, who usually consumed instant or fast food [23].

Young- and old-aged people eating alone need to be assigned a high priority for nutrition education and policy. Deficient intakes of calcium, vitamin A, and vitamin C and the low densities of those nutrients were the most critical dietary issues in the young-aged group. The young-aged group consumed a very simple diet with limited menu items, including fewer food ingredients. In particular, their INQs of vitamin A (0.89) and C (0.82) were the lowest among the groups, suggesting that they need to consume more vegetables and fruits. In a study about dietary behavior of Korean adults who eat alone in single households, young adults in their twenties and thirties consumed simpler meals, such as those comprised of single dishes or fast foods, compared to those consumed by people in their forties and fifties. Ramen was the most frequently consumed food when young adults eat alone [23]. In the old-aged group, intake levels of calcium, riboflavin, and niacin, as well, the nutrient densities of their meals were particularly low. The old-aged group ate relatively more menu items, but their DVS and DDS were low, and the percentage energy contribution of carbohydrates was high (70.2%), indicating their meals were not diverse and included ingredient repetition. Aging can be a risk factor for poor dietary quality, due to energy intake reduction and appetite loss with older adults who eat alone having a high risk of malnutrition [29]; therefore, education to improve dietary habits and intake of a quantitatively sufficient diet with more diverse ingredients, as well as support the provision of nutrient-balanced meals for elders who eat alone, is necessary.

The relatively lower quality of diet in men and the young-aged group could be explained by their frequent meal skipping and eating out as well as by their consumption of simple meals, as was identified in our study. The frequent meal skipping and eating out of men [30] and young adults [3132] was also reported in previous studies. Meal skipping [33] and frequent eating out [34] were associated with low intake of micronutrients, such as calcium, iron, and vitamin C, and frequent eating out can result in an elevated sodium intake [35]. The sodium intake of men (3,877 mg) was much higher than that of women (2,816 mg) in our study, and the young-aged group consumed the largest amount of sodium among the tested age groups. Interestingly, the high intake of sodium of young-aged group may be characteristic of solo eaters, because sodium intake of Korean adults is reported to be higher in adults aged 40–49 years, followed by older adults [30].

As dietary habits formed in the early adult period have influences on heath and nutritional status in old age, nutrition education for the young-aged group on the importance of regular and nutritionally balanced meals is essential. However, considering that the main reason for eating alone in young adults was reported to be a lack of time [1836], and young adults eating alone pursue convenience and cost-effectiveness and prefer to eat simple meals [37], a practical approach, such as educating young adults about dietary choice strategies for consuming more healthful convenience store food items, would be more effective. Convenience stores were one of the major eating places, and convenience store lunch boxes are frequently consumed when young adults eat alone [23]. However, it was reported that the nutritional quality of lunch boxes sold in Korean convenience stores were poor as a single meal [38]. Therefore, voluntary efforts by the food industry to develop healthy convenience meals, including small packages of fruits or vegetables customized for solo eaters, are essential, and related government policies are also necessary. In addition, such strategies could be effective if applied to men who eat alone and are not usually familiar with cooking, thus tending to eat simple meals. On the other hand, a policy-based approach may be more effective for older adults eating alone. Policies that encourage them to consume meals provided by senior welfare centers or expansion of meals-on-wheels programs could improve the nutritional intake of older adults who eat alone. In parallel, community-based nutrition education should be provided to encourage elderly solo eaters to maintain healthy meal consumption patterns.

In conclusion, deficiencies in the intake of energy and nutrients were common dietary issues for the subjects eating alone in this study. There were excessively low intakes of calcium, and intakes of energy and nutrients by men were higher than those for women, but men's dietary quality was poorer, showing a lack of food diversity as well as frequent meal skipping and eating out. The young-aged group showed similar dietary problems with vitamins A and C being the most deficient nutrients in their diet. The overall lower intake of food, the higher energy contribution from carbohydrates, and the low nutrient density of meals were the main dietary problems in old-aged subjects who ate alone. Their intakes of calcium, riboflavin, and niacin were notably low. The results of our study suggest that health-promotion campaigns and policies aimed at promoting healthy eating behaviors by solo eaters need to take into account gender and age differences when designing dietary strategies. In addition, young-aged adults and old-aged men need to be assigned a high priority within any nutritional policies developed for people who eat alone.

There are some limitations in our study. First, caution should be taken when interpreting and generalizing the results as typical energy and nutrient intakes of solo eaters, as the results were obtained by analyzing 24-hour recall data. Additionally, the meal partner variable in the 24-hour recall survey was included in the 2016 KNHANES; thus, we could not divide meals consumed alone from meals consumed with others. Second, it was impossible to determine the specific conditions associated with the subjects' usual consumption as a solo eater, such as duration and place of meals, snacking habits, etc. Despite the limitations, the results of this study could be used as a basis for strategies to improve the dietary life of people who eat alone. As the number of solo eaters will keep increasing in step with other social changes, further in-depth studies about gender and age distinct dietary behaviors should be undertaken. Studies into relevant differences in various sociodemographic characteristics, such as residence area, income level, household type, or job status, are also needed.