By Virginia Messina, RDN
While cost, taste and nutrition are all factors that drive food purchases, consumers are increasingly concerned about the carbon footprint of their dietary choices. Nearly 50 years ago, the book Diet for a Small Planet by Frances Moore Lappé emphasized the impact of food choices on water and land usage.1 More recently, researchers have also focused on how different diets impact greenhouse gas emissions (GHGE).
A number of studies suggest that production of protein from legumes requires less land, water, fuel and fertilizer than production of equivalent amounts of protein from meat.9,10 Although many factors affect these comparisons, soybeans appear to be a particularly efficient means of providing dietary protein. Estimates are that it takes 6-17 times less land, 4-26 times less water, and 6-20 times less fossil fuel to produce an equivalent amount of soy protein as it does from animal protein.
In looking at the impact of different protein-rich foods on the environment, it is important to consider protein quality. While legumes in general represent a useful strategy for planning healthful diets with a small carbon footprint, soybeans are particularly high in protein (even compared to other beans) and they also provide higher quality protein.3,4 As a result, growing an amount of rice required to meet dietary requirements for essential amino acids results in 20 times more GHGEs than growing the quantity of soybeans sufficient to meet these requirements. Likewise, production of either soybeans or corn results in similar levels of GHGEs on a per kg basis, but soybeans provide much greater amounts of protein. A recent study published in the journal Food Policy found that among all of the plant foods studied, soybeans produced the least GHGE per unit of protein provided.5
Although data are limited, individual soyfoods also take a smaller toll on environmental resources. Both soymilk6 and soy-based burgers7 have a smaller water footprint than cow’s milk and hamburgers and produce fewer GHGEs. Recent data also show tofu is a sustainable source of protein.8
As consumers shift toward more plant-based diets for environmental concerns, it is clear that soyfoods, because of the amounts of high-quality protein they provide, can play an important role in these diets.
References
1. Lappe FM. Diet for a Small Planet. New York, NY: Ballantine; 1971.
2. Scarborough P, Appleby PN, Mizdrak A, et al. Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK. Clim Change. 2014;125:179-92.
3. Messina MJ. Legumes and soybeans: overview of their nutritional profiles and health effects. Am J Clin Nutr. 1999;70:439S-50S.
4. Hughes GJ, Ryan DJ, Mukherjea R, Schasteen CS. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. J Agric Food Chem. 2011;59:12707-12.
5. González AD, Frostell B, Carlsson-Kanyama A. Protein efficiency per unit energy and per unit greenhouse gas emissions: Potential contribution of diet choices to climate change mitigation. Food Policy. 2011;36:562-70.
6. Product Carbon Footprint Summary. Tesco. Issued August 2012.
7. Hoekstra AY. The water footprint of animal products. In: D’Silva J, Webster J, eds. The Meat Crisis: Developing more Sustainable Production and Consumption. London, UK: Earthscan; 2010:22-33.
8. Mejia A, Harwatt H, Jaceldo-Siegl K, Sranacharoenpong K, Soret S, Sabaté J. Greenhouse gas emissions generated by tofu production: A case study. J Hunger Environmental Nutr. 2017.