Abstract
In order to understand the daily dietary intake of students in their 20 s, we conducted a nutritional survey of homemade box lunches (Bentou) prepared by the students, and commercial box lunches, as box lunches are a frequent lifestyle choice in Japan. The amounts of vitamin A, C, folic acid, and iron were 1.5 to 5.7 times higher in homemade box lunches than commercial ones; however, the homemade box lunches contained under 80% of the energies of commercial ones. Furthermore, less than 5% of homemade box lunches satisfied students' estimated energy requirements, and energy deficiency was more pronounced in men than in women. In women, the ratio of fat in nutritional intake exceeded the recommended value. We used a regression tree analysis, setting the calorific value as the objective variable. The results showed that the greatest contributory factor was the amount of carbohydrates. Changing the white rice into seasoned rice such as Takikomi-meshi, the amount of rice contained in the lunch increased, resulting in an increase in the carbohydrate content of the box lunches. Because it was easy to understand the relationship between the objective variable and the divided explanatory variable, a regression tree analysis could be an effective tool for nutritional evaluation.
