Objectives: This study first aimed to clarify the relationship between menus, nutrition quantity, and room temperature and leftover amounts of boiled rice, bread, and milk in school lunches. This study then aimed to provide a general linear model for predicting amounts of leftovers from these causal factors.
Methods: We surveyed records from school lunches (for 593 days in 2013–2016) from 12 elementary schools (approximately 7,000 children and teachers in total) in Takarazuka City, Hyogo Prefecture (cross-sectional survey). The survey focused on the following targets: amounts of leftovers, menu contents, nutrition quantity, and room temperature. Using the stepwise method multiple regression analysis was conducted for correlation estimation. We selected the amounts of leftover per portion of boiled rice, bread, and milk as dependent variables, and the kind of the menu converted to a dummy variable, room temperature, elapsed days from April 1, meal quantity, and nutrition quantity as independent variables.
Results: The analysis of leftovers of boiled rice indicated that there were high standardization coefficients β with room temperature (β=.56), boiled rice seasoned and mixed with ingredients (β=.40), curry (β=.39), and so on, with an adjusted coefficient of determination of R2=.62. Leftover bread was highly related to fried bread (β=.55), sandwiches (β=.36), room temperature (β=.34), bread seasoned and mixed with ingredients (β=.33), and so on, with R2=.53. Leftovers of milk had a unique relationship to room temperature (β=.63), with R2=.39.
Conclusions: The leftover amounts of staple food were related to room temperature, seasoning, and cooking methods. The leftover amounts of milk had a unique relationship to room temperature. A general linear model for estimating amounts of leftovers was obtained with an explanatory power of about 60%, 50%, and 40% for boiled rice, bread, and milk, respectively.
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