Environmental impacts of food (Poore & Nemecek, 2018)

Data is based on the largest meta-analysis of food system impact studies to date, from Poore & Nemecek's 2018 study.

The authors note the following about the scope of the studies included in this meta-analysis: "We derived data from a comprehensive meta-analysis, identifying 1530 studies for potential inclusion, which were supplemented with additional data received from 139 authors. Studies were assessed against 11 criteria designed to standardize methodology, resulting in 570 suitable studies with a median reference year of 2010. The data set covers ~38,700 commercially viable farms in 119 countries and 40 products representing ~90% of global protein and calorie consumption'.

Environmental impacts are compared across several metrics: land use (m2), greenhouse gas emissions (tonnes of CO2-equivalents), eutrophying emissions (grams of PO4-equivalents), freshwater withdrawals (liters), and scarcity-weighted water (liters) which are freshwater withdrawals weighted for local water scarcity.

All comparisons here are based on the global mean value per food product across all studies.

Comparisons can be made in functional units: here all comparisons are made as impacts per kilogram of product.

Comparisons are also made on the basis of nutritional units in two categories: per 100 grams of protein and per 1000 kilocalories.

Poore & Nemecek (2018) quantified a range of footprints in nutritional units: (1) protein products, which are compared per 100 grams of protein. Protein products include all meats, seafood, dairy, nuts, tofu and pulses. Grains are also compared here – despite being a low-quality source of protein – since a large share of global protein is derived from cereals.

(2) grains and staples, which are compared per 1000 kilocalories.

Poore & Nemecek (2018) do not provide data per 100g protein for food products which are not protein-rich, or kilocalorie measures for non-stale crops. To provide footprints for all products Our World in Data have filled these gaps by calculating footprints per nutritional unit using food composition factors from the FAO INFOODS International Database and Food Balance Sheets: http://www.fao.org/3/X9892E/X9892e05.htm#P8217_125315 http://www.fao.org/infoods/infoods/tables-and-databases/international-databases/en/

Footprints expressed per kilogram of food product can be converted to per unit protein or kilocalorie using data on the nutrient density of food products.

Where nutritional footprints are available from Poore & Nemecek (2018), this data has been used. Where there were gaps, this data has been calculated by Our World in Data. Poore, J., & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science, 360(6392), 987-992.