High-income countries, including the United States, need to shift dietary patterns to lessen the environmental burden of their food systems. Government programs, particularly large-scale initiatives like the National School Lunch Program (NSLP), offer significant opportunities to influence dietary habits and promote sustainability. The NSLP, with its substantial budget and reach, provides meals to nearly 40% of U.S. children daily. While the program is regularly evaluated for cost and nutritional quality, a comprehensive understanding of its aggregate environmental impact remains lacking. This study addresses this gap by providing baseline estimates of the environmental impacts of NSLP lunches, aiming to inform policy recommendations for creating more sustainable menus and fostering environmentally conscious food choices among students. Previous research on the environmental impacts of school lunches has primarily focused on European systems and global warming potential. While studies exist on the environmental impact of diets recommended by the U.S. Dietary Guidelines and of adult diets in the US, these lack the specificity needed to assess the impact of large-scale programs like the NSLP, especially considering the specific meal composition and nutritional standards designed for children and adolescents. Therefore, this research uses life cycle assessment (LCA) data tailored to the American food system, with a focus on domestically sourced products and incorporating multiple environmental impact categories (global warming potential, land use, water consumption, and eutrophication potential).

Existing literature extensively documents the environmental impacts of various diets, consistently showing that diets lower in animal products and higher in plant-based options generally result in reduced environmental burdens. Studies examining the environmental impacts of the U.S. Dietary Guidelines and American adult diets indicate that animal products, especially beef, are major contributors to greenhouse gas emissions, land use, and water consumption. However, these studies lack the granularity needed to assess the specific environmental impacts of the NSLP. Prior research on European school lunch programs offer valuable insights on this topic; however these studies are typically culture specific and focus primarily on global warming potential, making direct comparison with the U.S. context difficult. This study bridges this research gap by providing a comprehensive analysis of the NSLP, considering multiple environmental impact categories and the unique characteristics of school meals in the U.S.

This study utilized data from the School Nutrition and Meal Cost Study (SNMCS), a nationally representative survey of over 2.2 million lunches served in 1207 schools during the 2014-2015 school year. The SNMCS data included detailed information on the types and quantities of food served, allowing for a comprehensive assessment of lunch composition. Environmental impact data was sourced from the ecoinvent 3.6 database and an external study. Because ecoinvent 3.6 primarily contains LCIs for individual agricultural commodities rather than prepared foods, this study employed a robust method of linking commodity-level environmental impacts to the prepared foods and mixed dishes served in the NSLP. This process used recipes from the Food Commodities Intake Database (FCID) to translate the impacts from commodities to the final school lunches. A hierarchical decision tree was used to select the most appropriate LCIs, prioritizing U.S.-sourced commodities whenever possible. When direct matches between FCID commodities and ecoinvent LCIs were unavailable, proxy LCIs representing similar products were used. The researchers also modified existing LCIs to account for processing steps such as milling or oil extraction, reflecting the U.S. energy mix and agricultural inputs. Life cycle impact assessment (LCIA) calculations were conducted using the ReCiPe 2016 Midpoint Hierarchical method in openLCA software. The five most relevant impact categories for agricultural production were analyzed: global warming potential (GWP), land use, water consumption, freshwater eutrophication, and marine eutrophication. To account for variations in lunch size, all impacts and composition data were standardized to 1000 kcal. Lunch impacts were categorized into quintiles to understand the disproportionate contribution of high-impact meals, and statistical analyses were performed to identify differences in the composition of low-impact and high-impact lunches.

The average environmental impact per lunch was 1.5 kg CO2 eq. for climate change, 1.8 m²a crop eq. for land use, 0.055 m³ for water consumption, 0.24 g phosphorus eq. for freshwater eutrophication, and 3.1 g nitrogen eq. for marine eutrophication. Meat products were the dominant contributors to all impact categories (28-67%), with beef being particularly impactful despite accounting for only a small portion of the overall lunch mass. Dairy products were the second-largest contributors (17-29%), except for water consumption (7%). The top quintile of lunches (representing 20% of total lunches) accounted for approximately 40% of the total environmental impact across most impact categories, highlighting the potential for targeted interventions. High-impact lunches were characterized by greater servings of meat (especially beef), fruit juice, starchy vegetables, and protein foods, while low-impact lunches contained more dairy, whole grains, seafood, and nuts and seeds. Specifically, low-impact lunches had significantly more cheese and seafood, along with substantially greater amounts of whole grains, and markedly lower levels of animal protein compared to high-impact lunches. Meat accounted for 8% of total lunch mass, but contributed the most to all impact categories, emphasizing the significant influence of meat consumption on environmental outcomes. Poultry, due to its high frequency in school lunches and reliance on irrigated feed, was a major contributor to water consumption. Fruits and vegetables, while comprising a substantial portion of lunch mass, also contributed significantly to water consumption primarily from irrigation. Nuts and seeds, although having relatively low overall impacts, exhibited variability in water consumption across different types of nuts and seeds. The uncertainty analysis, comparing the results with different methods, showed that the ranking of commodities impact was consistent across all methods used. Proxy LCIs, representing a small percentage of the total environmental impact, provided a minimal effect on overall results.

This study's findings align with previous research emphasizing the significant contribution of animal products, particularly beef, to dietary environmental impacts. The substantial contribution of the top quintile of high-impact lunches underscores the potential efficiency gains from focusing policy changes on these meals. The observed higher proportion of whole grains, lower animal protein, and more seafood and nuts in low-impact lunches supports recommendations for dietary shifts to promote environmental sustainability. The considerable water consumption associated with fruits and vegetables, along with the significant impact of meat, especially beef, highlights the complexities of balancing environmental concerns with nutritional needs. The large proportion of water consumption attributable to fruits and vegetables underscores the need for a holistic approach, including considering water-efficient agricultural practices and sourcing strategies. The results emphasize the need for a multi-pronged approach to promoting sustainable school lunches, balancing environmental impacts with nutritional considerations and the practical realities of school food service.

This research offers the first comprehensive assessment of the environmental impacts of the U.S. National School Lunch Program. The findings demonstrate that a relatively small percentage of high-impact lunches are responsible for a disproportionate share of the overall environmental burden. The study strongly suggests that limiting beef servings and increasing whole grain requirements could effectively reduce the program's environmental footprint. Future research should explore cost-effectiveness, student acceptance, and logistical considerations for implementing these changes, including exploring alternative protein sources and innovative recipes. Further investigations into the optimization of food sourcing and agricultural practices to reduce water consumption, particularly for fruits and vegetables, are also warranted.

While this study used a nationally representative sample and employed a robust methodology, certain limitations exist. The use of water consumption data rather than a water scarcity metric might underestimate the true impact in water-stressed regions. The farm-gate or processor-gate system boundary for LCIs excludes post-production impacts. Data limitations prevented a full accounting of beef sourced from dairy systems, which could potentially lower the estimated impact of beef. Finally, the study did not explicitly account for food waste, which could add to the overall environmental burden.