Our food system is unsustainable. Animal farming and fishing accounts for 86% of global farmland, but contributes only 18% of our calorific intake . Feeding crops to animals introduces an unnecessary step into the food system. Instead of eating plants directly, we feed them to animals and then eat the animals. The calorie output of such a system will always be less than the input because energy is lost when animals respire and we do not eat all of their body parts. Including animals in our food system is not just inefficient, but also massively environmentally damaging. Animal products use more water, land and plant calories, and emit more greenhouse gases per calories produced (see Figure 1).
Figure 1: Environmental footprint of different foods, per 100 calories produced. Beef, pork, chicken, eggs, cow’s milk and soy beans      
- Poore, J. & Nemecek, T., 2018. Reducing food’s environmental impacts through producers and consumers. Science, 360 (6392), 987-992. – https://science.sciencemag.org/content/360/6392/987
- Cassidy, E.S., West, P.C., Gerber, J.S. and Foley, J.A., 2013. Redefining agricultural yields: from tonnes to people nourished per hectare. Environmental Research Letters, 8(3), p.034015. – https://iopscience.iop.org/article/10.1088/1748-9326/8/3/034015
- De Vries, M. and de Boer, I.J., 2010. Comparing environmental impacts for livestock products: A review of life cycle assessments. Livestock science, 128(1-3), pp.1-11. – https://www.sciencedirect.com/science/article/abs/pii/S1871141309003692
- Mekonnen, M.M. and Hoekstra, A.Y., 2012. A global assessment of the water footprint of farm animal products. Ecosystems, 15(3), pp.401-415. – https://link.springer.com/article/10.1007/s10021-011-9517-8
- Ercin, A.E., Aldaya, M.M. and Hoekstra, A.Y., 2012. The water footprint of soy milk and soy burger and equivalent animal products. Ecological indicators, 18, pp.392-402. – https://www.sciencedirect.com/science/article/abs/pii/S1470160X11004110
- Mohammadi, A., Rafiee, S., Jafari, A., Dalgaard, T., Knudsen, M.T., Keyhani, A., Mousavi-Avval, S.H. and Hermansen, J.E., 2013. Potential greenhouse gas emission reductions in soybean farming: a combined use of life cycle assessment and data envelopment analysis. Journal of Cleaner Production, 54, pp.89-100. – https://doi.org/10.1016/j.jclepro.2013.05.019
- U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. – https://fdc.nal.usda.gov.