Eating habits are influenced by many factors, including family, culture, availability, information, budget, and preferences. Although nutrition knowledge, including nutrition, nutrients, and food safety, are factors, there is a barrier to having it translate to actual behavior [12]. Nevertheless, it is recognized that nutrition knowledge has a weak but positive effect on healthy dietary habits [3456789]. Social cognitive theory [10] suggests that to change a specific behavior, a person needs to know what the required behavior is and how to perform it. Accurate knowledge about food and translating that into action are essential to a good diet. Eating habits are usually formed by adolescence. Hence, accurate knowledge and healthy habits will lead to favorable eating habits, which may prevent overweight or obesity over a lifetime [3].

The period from adolescence to adulthood, from ages 18–25 yrs, is also a period of independence from parents. During this time, adverse changes in diet and health, such as alcohol consumption, missing breakfast, and weight gain are often seen [11]. This is observed predominantly in students who leave their parents to attend university, who are adversely affected by the high cost of food and their own limited cooking experience [11].

In Japan, food and health were traditionally learned through home economics and health and physical education. These subjects are compulsory up to senior high school. Furthermore, since the Basic Law on Food Education was enacted in 2006, eating education (shoku-iku in Japanese) has become more common in schools and elsewhere. On the other hand, it is a science that deals with nutrients, such as proteins, carbohydrates, and fats, as well as metabolic processes in detail. In most high schools in Japan, the elective subjects of science differ greatly depending on the chosen career path, humanities/social studies courses, or science courses. This study examined the effects of high school elective science subject choice on nutrition knowledge and the effects on actual eating habits among college students in Japan.

Few studies have examined the relationship between nutrition knowledge and eating habits in the Japanese population. Nutrition knowledge was reported to have a positive effect on vegetable intake in children [7] and breakfast intake in adults [9]. To the best of the authors’ knowledge, this is the first study on this topic among college students in Japan. As in previous studies, nutrition knowledge appears to have a positive effect on actual eating behavior: a higher intake of fruits, vegetables, and breakfast was related to greater nutrition knowledge. In particular, the marked decrease in fast food consumption may be due to those students having greater nutrition knowledge and making decisions based on that knowledge.

Nutrition knowledge appears to reflect educational attainment indirectly. Bonaccio et al. [5] reported that a higher educational background indicates the following: greater nutrition knowledge in adults in Italy; greater intake of Mediterranean cuisine rich in fruits, vegetables, fish, and olive oil; decreased body mass index. In Japan, it was observed that the influence of education and economic background on food and health was smaller than that in Europe and the United States [15]. On the other hand, the gap between rich and poor has been widening since the beginning of 2000 in Japan, and the low-income group in Japan tends to have a higher intake of grains and a lower intake of vegetables, fruits, and fish [16]. In the future, Japan might follow the United States and Europe in having high socioeconomic health inequality.

The most significant differences between the sexes were generally observed in eating and exercise habits. This study found that female students consumed more vegetables, milk, and breakfast, suggesting that they often cook their own meals and are more careful about their diet. The main reason is that women were more concerned about their body shape [811]. On the other hand, girls consume many snacks and chocolate [11], while males have a higher consumption of soft drinks [17] and perform more exercise [8]. The intake of snacks and fast food was higher in female students living with their parents than in those living apart from their parents in this study. There may be economic reasons for this. The Tokyo Federation of Private University Faculty and Staff Unions reported that the allowance of college students today had dropped sharply in the last 20–30 yrs, from 124,900 yen in 1994 to 82,400 yen in 2021 [18]. Students might need to reduce the money they spend on food, particularly fast food, snacks, and sweets.

In this study, the food with the most different consumption patterns between those living with and apart from parents was fish, which was more commonly consumed by those students living with their parents. This is probably because cooking fish is difficult and malodourous, particularly in a typically small student apartment. In this study, 43.8% of males and 57.2% of females always ate breakfast, and the habit of skipping breakfast was more common among students living apart from their parents, especially males. According to the National Nutrition and Health Survey 2017 [19], 69.4% of males and 76.4% of females in their 20s always ate breakfast. The relatively higher incidence of skipping breakfast in these results was probably because of the students’ lack of time, poor cooking skills, and budget [11]. Many students are living alone for the first time, and they have to do everything, ranging from purchasing ingredients to cooking.

This study examined the effects of high school science subject choice on nutrition knowledge. Students who chose biology/chemistry, many of whom were students in the Faculty of Agriculture, had a significantly higher nutrition knowledge than the other groups. These students may also be more interested in food and health. On the other hand, the students who chose physics/chemistry, most of them majoring in mathematics, physics, or engineering, showed similar scores to those in the liberal arts and social sciences. The topic of nutrients and metabolism are included in the chapter on polymer substances in high school chemistry textbooks. This result is probably because engineering, mathematics, and physics students may have less interest in diet and nutrition. Teaching natural science, especially physics and chemistry, in relation to daily life can increase interest in students with low interest. Nutrition, health, and the environment are also useful for increasing literacy in the natural sciences because these topics interest certain scientists, engineers, and the general public.

The result of unclear responses to elective science subjects in 69 out of 587 (11.7%) students is probably because they enter college without having entrance examinations, such as English, mathematics, the national language, and science. Many colleges, including national universities, accept students without imposing entrance examinations for applicants. Therefore, they cannot recollect their high school science subjects.

In this study, the questions with correct answer rates of 90% or more were topics covered in elementary and junior high schools in Japan. On the other hand, there was a low understanding of the chemical structures of nutrients, recommended amounts, and types of food poisoning, at 20–30%. The energy metabolism, such as respiration and the chemical structure of nutrients, was not included in basic biology/chemistry classes in Japan. Without this knowledge, it would be difficult to understand the digestion and absorption of food and energy production. Furthermore, most students in Japan do not learn food safety and dietary intake standards at school. For the majority of the general public, even those without nutrition knowledge, it is possible to have a healthy diet to prevent lifestyle-related diseases, such as obesity, diabetes, and heart disease. Nevertheless, it is not enough to judge whether the nutrition information the media broadcasts can be trusted. A recent study reported that 66% of Norwegian college students and employees have difficulty understanding the nutrition information from the media [12].

This study had some limitations to this study. First, this study studied Japanese students. Hence, the findings may not apply to other countries with different cultures, diets, and education systems. In addition, the participants were college and vocational school students living in smaller regional cities in northern Japan. Therefore, the findings might differ. Second, the data could not be collected at once because of the coronavirus disease pandemic. The nutrition knowledge scores could be influenced by information from lectures and media after entering college. On the other hand, if the survey were conducted immediately after the students enter college, it would be impossible to investigate their lifestyle habits such as diet and exercise.

In conclusion, although the eating habits of college students are greatly affected by their living environment, greater nutrition knowledge appears to result in the higher consumption of vegetables, fruit, breakfast, and a lower consumption of fast food. The nutrition knowledge scores of those who took biology and chemistry in high school were relatively higher than those who did not choose these subjects. Most students appeared to have basic nutrition knowledge, but they had an insufficient understanding of the chemical structure of nutrients, types of food poisoning, and the recommended daily amounts of food. Although biology and chemistry classes in high school help give students some nutrition knowledge, specialized food education may be required to enable them to make good dietary lifestyle choices.