Performing full life cycle assessment on foods and diets is a data- and resource-intensive undertaking and as a result many studies tend to adopt a simplified approach, for example by limiting the number of food studied (in the case of diets), using proxy data, or limiting the system boundaries (cradle to farm gate; cradle to retailer – ie. not the full cradle to the consumer’s mouth).
The aim of this study was to investigate how simplifications in LCAs of foods and diets affect the accuracy of impact results. The LCA study compared three diets (average, healthy and vegetarian) using six methods with different system boundaries; three of these methods are simplified methods which the study authors have themselves developed. The reference ‘gold standard’ approach used in the paper is entitled Fc-m (ie. a full LCA, from cradle to mouth) - see table, copied, which summarises the different approaches. The goal of this paper was to establish recommendations on which methods to use, depending on study goals, to obtain the best trade-off between result accuracy and available resources.
The analyses were made using ISO-compliant LCA data for 105 foods, using the same data for each of the six methods above.
The study found that using cradle-to-retailer and cradle-to-farm-gate system boundaries instead of cradle-to-mouth boundaries resulted in underestimates of impact of approximately 30% and 70%, respectively. See figure, copied.
It also found that depending on the purpose of the study (whether a food or a whole diet was being assessed) simplified approaches worked quite well, although there was variation depending on the environmental impact being assessed.
The study concluded with a flow chart (see figure) intended to aid decision making as to which method to use so as to obtain the best trade-off between available resources and the robustness of LCA results.
The number of Life Cycle Assessment (LCA) studies on foods and diets steadily increases. However, due to lack of data on food products as well as time and resource constraints, many of these studies ignore part of the system (e.g. cooking and waste in the household), which may lead to underestimating impacts greatly. This LCA study compared diets using six methods with different system boundaries; three of these are simplified methods we developed. The aim was to identify which method best optimizes data collection for life cycle inventories from cradle to human mouth of food products and diets. The principle behind the three simplified methods was that, for many foods and impact categories, the farm (or fishery) is the life cycle stage that contributes most to impacts. One average, one healthy and one vegetarian diet, each composed of up to 105 foods, were assessed. Climate change, cumulative energy demand, eutrophication, acidification and land occupation impacts were estimated. Recommendations are given on which methods, depending on study goals, offer the best trade-off among available resources (time, money, and knowledge), while providing the required robustness of results. Compared to a full LCA, simplified LCA methods can yield more accurate results at a lower cost of data collection.
Pernollet, F, Coelho CRV, van der Werf HMG (2016). Methods to simplify diet and food life cycle inventories: Accuracy versus data-collection resources, Journal of Cleaner Production
Read the full article here (paywall).
For more studies on LCAs, please look in our research library and the category Life Cycle Analysis.