Easy metrics like 'it takes a gallon of gas to make a pound of beef' or 'it takes 140 liters of water to make a cup of coffee' get mainstream media because they are outrageous. They are outrageous because they are completely wrong.

What is the 'real' cost of eating beef? Are the other animal or animal-derived foods better or worse?

A new method attempts to compare the environmental costs of various foods and the authors believe they came up with some surprisingly clear results. The team looked at the five main sources of protein in the American diet: dairy, beef, poultry, pork and eggs. Their idea was to calculate the environmental inputs – the costs – per nutritional unit: a calorie or gram of protein. The main challenge the team faced was to devise accurate, faithful input values.

For example, cattle grazing on arid land in the western half of the US use enormous amounts of land, but relatively little irrigation water. Cattle in feedlots, on the other hand, eat mostly corn, which requires less land, but much more irrigation and nitrogen fertilizer. The researchers needed to account for these differences, but determine aggregate figures that reflect current practices and thus approximate the true environmental cost for each food item.  

The inputs the researchers employed came from the US Department of Agriculture databases, among other resources. Using the US for this study is ideal, says Milo, because much of the data quality is high, enabling them to include, for example, figures on import-export imbalances that add to the cost.

The environmental inputs the team considered included land use, irrigation water, greenhouse gas emissions, and nitrogen fertilizer use. Each of these costs is a complex environmental system. For example, land use, in addition to tying up this valuable resource in agriculture, is the main cause of biodiversity loss. Nitrogen fertilizer creates water pollution in natural waters.

When the numbers were in, including those for the environmental costs of different kinds of feed (pasture, roughage such as hay, and concentrates such as corn), the team developed equations that yielded values for the environmental cost – per calorie and then per unit of protein, for each food.

The calculations showed that the biggest culprit is beef. The surprise, and therefore the skepticism, comes from the size of the gap: In total, they found that eating beef is more costly by an order of magnitude – about ten times on average – to the environment than other animal-derived foods, including pork and poultry. Cattle require on average 28 times more land and 11 times more irrigation water, are responsible for releasing 5 times more greenhouse gases, and consume 6 times as much nitrogen, as eggs or poultry.

Poultry, pork, eggs and dairy all came out fairly similar. That was also surprising, because dairy production is often thought to be relatively environmentally benign. But the research shows that the price of irrigating and fertilizing the crops fed to milk cows – as well as the relative inefficiency of cows in comparison to other livestock – jacks up the cost significantly. 

Dr. Ron Milo of the Weizmann Institute of Science's Plant Sciences Department believes that this study could have a number of implications. In addition to helping individuals make better choices about their diet, it should hopefully help inform agricultural policy. And the tool the team has created for analyzing the environmental costs of agriculture can be expanded and refined to be applied, for example, to understanding the relative cost of plant-based diets, or those of other nations.

In addition to comparisons, it can point to areas that might be improved. Models based on this study can help policy makers decide how to better ensure food security through sustainable practices. 



Pubished in PNAS. Source: Weizmann Institute of Science