**5. Conclusions**

Food systems are heavily reliant on energy resources, especially non-renewable resources. This causes significant amounts of GHG emissions. In this study, the efficiency of the Spanish agri-food system was addressed from an energy and environmental perspective. Firstly, an LCA was performed to determine the PED and GWP impact results of the food basket with the representative food products consumed in and out of home by a Spanish adult in a year. Thereafter, the EROI indicator was used to perform an energy-based efficiency assessment. Finally, DEA was coupled with LCA to include environmental aspects in the efficiency assessment. Both approaches provided similar results, suggesting a high correlation between PED and CO2 eq. emissions. Best results were obtained for the categories of sweets and vegetable oils ( φ = 1), while vegetables, fish, eggs, and meat exhibited the lowest efficiency, below 0.1. As expected, animal-based products required more energy resources in their production than vegetable-based products. However, it is important to mention that these types of food (i.e., sweets and vegetable oils) are considered "empty kcals", and their nutritional value is very low, whereas eggs, meat, and fish are most valuable in terms of nutritional value. Therefore, it would be interesting to considering other nutrients, such as proteins, in future assessments. On the other hand, the unexpected results for vegetables are due to the inclusion of processed products in this category. On average, approximately 70% energy-saving potential is estimated for the Spanish agri-food system if it were to be efficient, with a similar reduction in related GHG emissions. These results sugges<sup>t</sup> the need for improving the efficiency of the FSC by introducing circular economy strategies, such as establishing appropriate food waste managemen<sup>t</sup> measures and the consequent reduction of FLW. Therefore, the methodology proposed is a useful tool for promoting the circular economy of food. The introduction of nutritional- and energy-based criteria, in addition to the environmental pillar, provides an integrated framework for proposing integrated reduction targets. However, as ongoing research, other criteria, such as economic and social aspects, could be considered. From the DEA results, it is possible to define specific strategies for the categories revealing larger inefficiency scores, such as meat, eggs, fish, and vegetables. In terms of the life-cycle processes, the primary production phases were the major contributors to PED for eggs (85%), meat (65%), and fish and seafood (59%), due to the production of feed (corn, soybean, and wheat) in the case of eggs and meat, and the use of diesel and electricity in the fishery and cultivation stages, respectively. On the other hand, the household stage was the main contributor for vegetables (52%) due to the use of electricity for cooking and cooling.

Finally, we can establish that DEA is a useful tool for energy optimization, identifying efficient and inefficient food systems. This approach may be adopted by institutions, policy-makers, and producers as a helpful instrument to support decision-making and improve the sustainability of agri-food systems.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1073/11/12/ 3395/s1. Section S1: Food Balance Sheet Construction; Section S2: Avoidable and Unavoidable Food Loss Calculation; Section S3: Nutritional Food Loss Calculation; Section S4: Example of Calculations According to the Methodologies Presented in Section 2.

**Author Contributions:** Conceptualization, R.A.; investigation, I.G.-H., J.L., and D.H.; methodology, L.B.-B., and I.V.-R.; formal and technical analysis, I.V.-R., J.L., P.F., A.B., A.I., L.B.-B., and R.A.; supervision, M.M., J.L., and R.A.; writing and editing of manuscript, I.G.-H. and J.L.

**Funding:** This work was carried out under the financial support of the Project Ceres-Procom: food production and consumption strategies for climate change mitigation (CTM2016-76176-C2-1-R) (AEI/FEDER, UE) financed by the Ministry of Economy and Competitiveness of the Government of Spain.

**Acknowledgments:** The authors want to acknowledge the Industrial PhD Program 2017 (BOC Nº200 18/10/2017) and to the UNESCO Chair in Life Cycle and Climate Change.

**Conflicts of Interest:** The authors declare no conflict of interest.
