Fruits and Vegetables Displace, But Do Not Decrease, Total Energy in School Lunches

Background: The high overweight and obesity prevalence among US children is a well-established public health concern. Diet is known to play a causal role in obesity. Increasing fruit and vegetable (FV) consumption to recommended levels is proposed to help reduce obesity, because their bulk and low energy density are believed to reduce energy-dense food consumption (volume displacement hypothesis). This study tests this hypothesis at the lunch meal among upper-elementary students participating in a Farm to School (F2S) program. Methods: Digital photographs of students' school lunch trays were visually analyzed to identify the food items and amounts that were present and consumed before and after the meal. Using the USDA Nutrient Database, total and FV-only energy were calculated for each tray. Analysis of total-and non-FV energy intake was performed according to (1) levels of FV energy intake, (2) FV energy density, and (3) previous years of Farm to School programming. Results: Higher intake of FV energy displaced non-FV energy, but total energy did not decrease across FV energy intake groups. High-FV-energy-density trays showed lower non-FV energy intake than low-FV-energy-density trays (470 +/- 179 vs. 534 +/- 219 kcal; p < 0.0001). Trays from schools with more previous years of F2S programming decreased total and non-FV energy intake from school lunches (p for trend < 0.0001, both). Conclusions: Increased FV consumption reduces non-FV energy intake, but does not reduce total energy intake. Therefore, this study does not support the volume displacement hypothesis and suggests calorie displacement instead.