The International Journal of Life Cycle Assessment

, Volume 15, Issue 8, pp 794-805

First online:

Life cycle assessment of the average Spanish diet including human excretion

  • Ivan MuñozAffiliated withDepartment of Hydrogeology and Analytical Chemistry, University of AlmeríaUnilever, Safety & Environmental Assurance Centre Email author 
  • , Llorenç Milà i CanalsAffiliated withUnilever, Safety & Environmental Assurance Centre
  • , Amadeo R. Fernández-AlbaAffiliated withDepartment of Hydrogeology and Analytical Chemistry, University of AlmeríaInstituto Madrileño de Estudios Avanzados, IMDEA Agua, Parque Científico Tecnológico de la Universidad de Alcalá, Edificio ZYE

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Background, aim and scope

The aim of this work is to find out to what extent human excretion is relevant in the context of a Spaniard’s overall food intake. A case study dealing with the average Spanish diet is carried out, including the whole life cycle of food: agricultural and animal production, industrial processing, distribution and retail, home storage and cooking, solid waste management and human excretion.


An extensive literature review was carried out to obtain life cycle assessment (LCA) data for Spanish food products. Also, the Danish LCA Food database and other European literature sources were used, along with ecoinvent background data. Human excretion and wastewater treatment were accounted for with a specific model recently developed, which required calculating the average nutritional composition of the Spanish diet. Concerning life cycle impact assessment, only three impact categories, namely global warming potential (GWP), acidification potential (AP) and eutrophication potential (EP), were assessed, along with primary energy use (PEU) as environmental indicator.


Food production clearly appears as the main hotspot in the Spanish diet. Human excretion, along with further wastewater treatment, is not a negligible process in EP and GWP, where it is the second most important source of emissions, with 17% of the overall emissions. However, if biogenic CO2 emissions are not taken into account, the contribution of human excretion to GWP becomes very small (3%). The contributions to AP (2%) and PEU (3%) are also very small.


The main limitation of this study is the lack of representative data to cover food production in Spain. Nevertheless, our total estimates for GWP and PEU per person per year are in accordance with previous studies, as well as the identification of animal food as a main source of environmental impacts. These studies achieve similar results without including human excretion, but concerning EP, there are no previous studies focusing on this impact category at the diet level.


Food production is the most important life cycle stage in the Spanish diet, especially meat and dairy products. Nevertheless, human excretion as a life cycle stage has been found to be important in EP due to the emissions of nutrients in treated sewage.

Recommendations and perspectives

These results show that excretion should not be overlooked in LCA studies dealing with diet shifts and studies aimed at identifying the life cycle hotspots of food products.


Carbon cycle Food Human excretion Life cycle assessment Nutrient cycle Wastewater treatment