Towards efficient use of resources in food systems : Exploring circular principles and strategies

Summary

Natural resources for food production, such as land, phosphate rock and fossil energy, are scarce. Despite their scarcity, these resources are currently inefficiently used in the food system. The objective of this thesis was to understand the combined effects of technical and consumption strategies, to reduce the use of natural resources in a food system. To this end, we first reviewed 12 life cycle assessments studies that explored various diets. We concluded that the ‘daily’ or ‘yearly’ diets instead of meals should be used to compare environmental impacts of diets. We also found that accounting for nutritional quality of the diets hardly affected our comparison of environmental impacts of diets varying in % of animal-source food. We then explored the minimum requirements of land, phosphorus (P) and energy independently to feed a human population with diets varying from 0% protein from animals (PA) (i.e. a vegan diet) to diets containing 80% PA, using an integrated food systems approach. Our material and nutrient flow model was a conceptual representation of a food system that was parameterised with crop and animal production data from the Netherlands. We assumed that there was no import and export of food and feed. While the Dutch food system is not representative of all food systems in the world, sensitivity analyses demonstrated that the principles deduced from our model results also hold for other food systems. Results indicated that land is used most efficiently if people consume ca. 12% of PA, especially from milk. The role of animals in such a land-based diet is to convert co-products from crop production and the human food industry, otherwise not used within the food system, into milk and meat. The optimal %PA in the human diet depends on population size and the relative share of land unsuitable for crop production. Recycling of human excreta showed most potential in reducing P waste, followed by prevention and finally recycling of agricultural waste. Fully recycling P reduces mineral P input by 90%. The optimal amount of animal protein in the diet depended on whether or not P waste from animal products was fully prevented or recycled: if it was fully prevented or recycled, then a small amount of animal protein in the human diet resulted in the most sustainable use of P, but if it was not fully prevented or recycled, then the most sustainable use of P results from a complete absence of animal protein in the human diet. In situations with anaerobic digestion and/or waste prevention, energy input continuously increased with increasing %PA, whereas if none of these strategies were applied, energy input was minimised at about 15% PA. Account must be taken of combined effects of technical and consumption strategies to reduce the use of natural resources in food systems. It requires efforts from all actors to develop a food system that is able to supply the global population with safe and healthy food within environmental limits.