School beverage environment and children's energy expenditure associated with physical education class: an agent-based model simulation

Background: Physical activity contributes to children's energy expenditure and prevents excess weight gain, but fluid replacement with sugar-sweetened beverages (SSBs) may diminish this benefit. Objective: The aim of this study was to explore the net energy expenditure (EE) after physical education (PE) class given the competition between water and SSB consumption for rehydration and explore environmental factors that may influence the net EE, e.g. PE duration, affordability of SSB and students' SSB preference. Methods: We built an agent-based model that simulates the behaviour of 13-year-old children in a PE class with nearby water fountains and SSB vending machines available. Results: A longer PE class contributed to greater prevalence of dehydration and required more time for rehydration. The energy cost of a PE class with activity intensity equivalent to 45 min of jogging is about 300 kcal on average, i.e. 10-15% of average 13-year-old children's total daily EE. Adding an SSB vending machine could offset PE energy expenditure by as much as 90 kcal per child, which was associated with PE duration, students' pocket money and SSB preference. Conclusions: Sugar-sweetened beverage vending machines in school may offset some of the EE in PE classes. This could be avoided if water is the only readily available source for children's fluid replacement after class.