Due to recent changes in social structure and way of thinking, single-person households are on the rise worldwide. The survey on single-person households in England and France showed that the increase in urban single-person households was striking and its major reasons were divorce and late marriage [1], and according to Mulder [2], it was reported that living arrangements of living alone or living together without marriage is on the rise in Netherland as well due to parents' demand for independence. According to Korea Statistics [3], single-person households are increasing from 6.3% in 1980 to 15.5% in 2000, to 19.9% in 2005, and the number of single-person households was 23.9% in 2010, exceeding, for the first time, the proportion of the traditional four-person households which was 22.5% [4]. Also in Japan, it shows steady increase from 19.8% in 1980, to 27.6% in 2000, and to 29.5% in 2005 [5] and in China, according to the 5th Census Report for People's Republic of China [6], the number of single-person households in Beijing in 2000 was 494,553 out of 28,273,35 single-person households in China, which was noticeably large compared to 598,327 four-person households. As such, the number of singles is on the rise in Korea, Japan, and China, three countries in Northeast Asia, and the importance of singles in the society is growing accordingly.

In the case of traditional or dual-income families, family members gather and have meals together, able to consume various and plentiful foods, and often have homemade meals together on the weekends or holidays; however, in the case of singles, many skip meals, consume instant foods, or a consume limited variety and insufficient amounts of food because they usually eat alone [7]. The reality is that singles encounter considerable difficulties in their dietary lifestyles.

Although a variety of factors including health, psychological state, and spirituality, social, mental and economic conditions may contribute to life satisfaction, the pleasure of eating can account for a large part of the quality of life as Lee [8] reported that the emotional stability related to meals and the pleasure of eating have a significant effect on the quality of life of the elderly staying home. Consequently, the interest in the quality of life of singles is increasing, but the research on the relationships related to their diet-related quality of life is scarce.

Therefore, the present study attempted to provide basic data to improve the quality of life of singles by analyzing dietary styles of Korean singles, along with the singles in Japan where the development of convenience food advanced earlier than Korea, and singles in china where rapid economic growth occur recently, and comparing the relationships between the current state of convenience food use and the factors that affect satisfaction and the quality of life.

The results of the comparative study on the convenience food satisfaction and quality of life depending on the dietary style of Korean, Japanese, and Chinese singles are as follows: As a result of testing Hypothesis 1, the convenience-oriented style had a positive effect on convenience food satisfaction among Korean and Japanese singles, but not among Chinese singles. In a number of earlier studies [15,19,20], the instant food-oriented and convenience-oriented lifestyles were generally associated with higher satisfaction with convenience food, such as instant food, processed food, and Home Meal Replacements (HMR). This is also in line with Chung [14] finding that convenience eating is related to meals and snacks that give the consumer more time to do other activities. Hence, convenience food satisfaction is inferred to be high among those with the convenience-oriented diet style. The health-oriented style among Japanese singles had a significantly positive effect on the overall convenience food satisfaction and among Korean singles, the health-oriented style was found to have a high level of satisfaction for HMR and processed food. Eco-friendly convenience food products with safety and sanitation are thought to be increasing along with the recent rise in the interest in health, and the singles' satisfaction are increasing accordingly. Japan's HMR industry is particularly well-developed, and cooking areas are openly visible within the establishments, leading customers to feel as if the food was freshly made and is safe [15]. Therefore, Japanese singles who are concerned with their health also displayed a high degree of satisfaction with convenience foods. However, Chinese singles showed the overall negative effect, indicating that singles with the health-oriented diet style in China are low in satisfaction for convenience food. In accordance with Chinese consumers' interest in healthy functional food increases [21], it speculated that their idea of convenience food showed negative. Chinese singles' economy-oriented style generally had higher fast food satisfaction than two other countries, and the economy-oriented Chinese singles who take price into consideration in maintaining their dietary style were particularly high in fast food satisfaction. The gourmet-oriented style among Korean singles were found to be low in satisfaction for processed food and fast food, and therefore, the development for taste improvement of convenience food is deemed essential.

As a result of testing Hypothesis 2, in terms of HMR satisfaction, out of three countries, Japanese singles had the lowest satisfaction for the price, indicating that the price of HMR somewhat influenced economy satisfaction in quality of life. Among Korean singles, processed food satisfaction had a significantly positive effect on the overall quality of life, which is thought to be the positive effect of singles' processed food satisfaction on quality of life. It is inferred that singles often want simple and easily prepared meals particularly due to their characteristics as singles, and processed food improves their quality of life due to being able to save time, efforts, and money invested in preparing a meal by using processed food.

Among Chinese singles in particular, the higher fast food satisfaction was associated with health satisfaction, indicating that they are currently focusing on the positive effect rather than negative effect of fast food. As seen in the case of Yonho-Doujian(永和豆漿), a Taiwan-based restaurant chain which developed Chinese breakfast foods as fast food and operates around the concept of "healthy food which can be eaten by the whole family for their entire lives" [22], cases in which so-called fast foods are being developed with the health of the consumer in mind are gradually increasing and this trend can have a notable influence on the health aspect of quality of life.

As a result of testing Hypothesis 3, the convenience-oriented style was found to have a significantly negative effect on overall quality of life among Korean singles. It is thought that Korean singles often do not feel the pleasure of eating which a large part of life, as they often take the simple meals, and are low in satisfaction for communication with others during a meal as they often eat alone and accordingly the psychological, economic and health satisfaction appeared to be low as well. Among Chinese singles, the convenience-oriented style was found to have a significantly negative effect on psychological satisfaction. Among the many factors which influence quality of life, the effect of loss of appetite on quality of life has been documented [23], and it may be argued that the relative importance of dietary lifestyle in quality of life is considerable. Therefore, convenience-oriented singles who are unable to prepare meals with other family members or do not have sufficient time to eat and thus often consume light meals, precooked foods, or processed foods often suffer from psychological disorders such as anxiety or depression.

However a significantly positive effect on overall quality of life among Japanese singles. In contrast to Korean singles, among Japanese singles, the more efficient use of time and simpler convenience-oriented style are thought to be associated with overall life satisfaction. The health-oriented style was found to have a significantly positive effect on overall quality of life among Japanese singles. Kim [24] set items such as regular check-ups or exercise, alcohol consumption, skipping breakfast, dietary fiber consumption, and a high-fat diet as health promotion behavioral levels and researched the correlation between these behavioral levels and quality of life. She found that the higher the health promotion behavior levels, the higher the quality of life, results which are similar to those of this study. In addition, according to the research of Kim [25], the more one's lifestyle actively responds to one's environment in order to elevate one's health, the stronger the correlation between all kinds of quality of life factors such as health accountability, exercise, interpersonal relationship management, and stress management. It was also found that the quality of life of middle-aged women increased the more immersed they were in a health promotion lifestyle. The results of this study are also related to such results.

The economy-oriented style was found to have a negative effect on economy satisfaction in quality of life among Japanese singles and Chinese singles. The costs of cooking at home or purchasing organic food products for singles is more burdensome than purchasing processed foods or precooked foods, and it appears that economic-oriented singles may have a low degree of economic satisfaction in their quality of life because they pursue inexpensive dietary lifestyles.

The number of singles in Korea, Japan, and China has been consistently increasing in recent years, and there is a need for continuous interest in their healthy dietary lifestyles in terms of convenience, economy, and taste. Furthermore, various social assistance programs and further research must be conducted in order to raise the quality of life of these singles.