Accuracy of portion size estimation by canteen and school staff on school meals

Abstract

Abstract Background A correct estimation of food portions is essential for canteen and school staff involved on school meals, affecting children's nutritional status. Thus, it is essential evaluate food portions perception, aiming to improve benefits provided by school meals. Methods This study focused on 35 Portuguese public schools of the city of Porto, that daily offer 6500 lunches to children aged 3 to 10 years old. At each school, the food handler responsible for platting at canteen and a school staff member responsible for the daily supervising of school meals was included. In line service, a meal composed by protein component, side dish, vegetables, bread and fruit was randomly selected. Participants estimated food portion sizes in grams by observing portions of each meal component, posteriorly weighed using a digital scale. Estimation and real values were compared for both participants. Results A total of 175 meal components were evaluated by 70 observers. Canteen staff underestimated, on average, 36.9g of side dish (p = 0.010), 63.7g of fruit (p < 0.001) and 16.2g of bread (p < 0.001). School staff underestimated, on average, 42.1g of side dish (p = 0.043), 70.7g of fruit (p < 0.001) and 24.1 of bread (p < 0.001). Dish type influenced the portion estimation by school staff with regard to the side dish (p = 0.026), being visual estimate of composed dishes closer to real values compared to non-composed dishes. Canteen staff attend to in-situ kitchen better estimated the portions of fruit and bread. Conclusions Food portions of side dish, bread and fruit were underestimated, so it can be concluded that the visual perception of canteen and school staff on school lunch is not accurate. It is essential training to ensure adequate portions serving in school meals and promoting actions for school staff to avoid the encouragement of overconsumption by children. These actions could have a great public health impact either on nutritional status adequacy and on food waste reduction. Key messages Food portions estimation of canteen staff was closer to real portion compared with school staff. It is huge the difficulty in visually estimation of food portions on school meals.