Food loss and waste in the environmental assessment of diets

The impact of a diet can be calculated using a Life Cycle Assessment (LCA) approach. Food loss and waste (FLW) contribute significantly to the environmental impact of food products, yet this is not always adequately addressed in dietary impact studies. This paper presents a structured scenario analysis that examines how commonly used dietary data sources, system boundaries, and FLW assumptions interact and affect the calculated dietary impacts. Specifically, we examine scenarios formed by combining three methodological dimensions: (i) the dietary data used to define the diet (food intake, food expenditure, or food availability quantities), (ii) the system boundaries chosen for the environmental assessment (cradle-to-farm, cradle-to-retail, or cradle-to-consumer/farm-to-fork), and (iii) the inclusion or exclusion of FLW in the impact assessment, distinguishing between supply chain and consumer waste. To facilitate the analysis, we broke down the LCA calculations into simplified analytical formulae and investigated how the different combinations of these three dimensions (resulting in 21 possible scenarios) affected the LCA calculations. A case study on potato wedges is used as an illustrative example to demonstrate the practical implications of the different scenarios. We found that only one scenario could accurately calculate dietary impacts. For twelve scenarios, it is clear that the impacts would be under- or overestimated. For the remaining eight scenarios, it is less straightforward; we can only conclude that there is likely to be an under- or overestimation of the impacts without being able to say which. For the case study, the impacts ranged between an overestimation of 14% and an underestimation of 88%. The recommended approach for calculating dietary impacts is to use data representing food intake quantities (thus excluding any FLW quantities) and apply a farm-to-fork system boundary that considers FLW along the supply chain and at the consumer. If only food availability or expenditure data is available, the data must be converted to reflect food intake quantities. This paper highlights the importance of methodological choices related to dietary data and environmental assessments, and provides clear guidance to scientists in making transparent and consistent methodological decisions.