The present study was conducted to examine the relationship between the bone mass of students of junior high schools that serve/do not serve school lunches and their dietary/lifestyle habits. The subjects were 428 third-year students of three junior high schools: A in Saitama Prefecture and B in Tokyo Prefecture that serve school lunches, and C in Kanagawa Prefecture that does not. A survey to measure the mass of the calcaneus using ultrasonic waves and a self-completed questionnaire survey were conducted to examine their dietary/lifestyle habits and awareness of physique.

A low body weight, a cause of a low bone mass, is one of the risk factors for osteoporosis. Among students of the three schools, 86.7％ of females and 63.8％ of males with a “normal” physique stated that they were fat. It is necessary to help students understand the importance of maintaining a healthy weight.

The rates of students whose Z score (a type of bone mass index, or deviation, calculated by comparing the bone mass with a standard value for people of the same age and sex) was lower than 90％ were 19.1 (A), 23.7 (B), and 33.7％ (C) ; there were significant differences among the three schools, with the rate in school C being the highest. There were also significant differences in the frequencies of eating or drinking milk, yogurt, and green and yellow vegetables among the schools; the frequencies in School C were the lowest. Among the three schools, the rate of students who had developed exercise habits in the high bone mass group was higher than that of students in the low bone mass group.

The results of the study suggested that the rate of students with a low bone mass was higher in junior high schools that do not serve school lunches, compared with schools that had introduced a school lunch system. It is necessary to provide junior high schools that do not serve school lunches with appropriate support to encourage students to consume milk and dairy products, which are rich in calcium, and green/yellow vegetables, and develop healthy exercise, dietary, and lifestyle habits for the prevention of osteoporosis.