HOW GREEN IS YOUR KOSHER CHICKEN?: Packages of organic kosher chicken at Brooklyn, N.Y.'s Pomegranate kosher supermarket
Emily Gertz

When food writer Lisë Stern needs fresh vegetables to roast with a chicken, she bicycles to the green market near her Cambridge, Mass., home where local farmers sell organically grown produce. Once back in her kitchen, she prepares the meal using knives, bowls, utensils, a cutting board and a roasting pan dedicated solely to cooking with meat, and serves it to her two teenage sons (her 11-year-old daughter is a vegetarian) on glass plates never touched by milk, cheese or other dairy foods.

Stern, the author of How to Keep Kosher: A Comprehensive Guide to Understanding Jewish Dietary Laws, is one of a million or so American Jews (out of around six million total) who keeps her kitchen year-round according to the laws of kashruth, or kosher. She's also interested in the environment. So how does keeping kosher contribute to—or undermine—her efforts to go a little lighter on the planet?

In 2007 kosher foods were worth $12.5 billion of the $500-billion retail food market, according to market research firm Mintel. It isn't only Jews: According to marketing company Lubicom, the 10.2 million Americans who eat kosher foods include around three million Muslims, whose halal dietary rules overlap with kosher ones.

Kosher rules state: those who keep kosher eat traditionally domestic fowl like chicken and turkey; most fish with fins and scales—that means no shrimp, crab or lobster; and mammals that both chew their cuds and have split hooves, which includes cows and sheep, but not pigs.

What would the environment look like if everyone kept kosher? Per capita, Americans consume about 63.5 pounds (29 kilograms) of beef, 48.2 pounds (22 kilograms) of pork and 59 pounds (27 kilograms) of chicken per year, according to the U.S. Department of Agriculture. They also down 54 pounds (25 kilograms) of fish and shellfish, including about four pounds (two kilograms) of shrimp (the U.S.'s most popular seafood), according to the National Oceanic and Atmospheric Administration's Marine Fisheries Service.

So how does a kosher diet fare as one that is ecofriendly? Time for some calculations: first, let's assume that kosher vegetarians would still steer clear of meat in any quantity, even if they did not keep kosher, meaning that observing the rules would have no impact. Let's also assume that kosher omnivores consume the same average weight of meat per capita as other Americans, but replace pork with either beef or chicken. That would have an impact. Solely in terms of how much grain livestock consume, producing a pound (0.45 kilogram) of beef releases 13.67 pounds (6.2 kilograms) of greenhouse gases, compared with around 6.75 pounds (3.1 kilograms) to produce a pound of pork, and 3.37 pounds (1.5 kilograms) for every pound of chicken—and this does not even take into account the other factors in meat's carbon footprint, from deforestation for pasturage to shipping it to market. Globally, meat production generates 18 percent of the world's man-made greenhouse gases, according to the United Nations Food and Agriculture Organization.

That means replacing nonkosher pork with an equivalent 48 pounds (22 kilograms) of beef releases about 1,504 pounds (682 kilograms) of greenhouse gases annually, compared with 1,378 pounds (625 kilograms) of carbon a year for the pork-friendly eater.