A dietary change toward veganism is one of the most powerful, tangible ways to reduce one’s individual, household, or community ecological footprint. According to Environmental Working Group data, if a four-person family stops eating meat and cheese for one week, they benefit the environment as much as if they stopped driving their car for 35 weeks.

Carnivores eat flesh from domesticated or wild animals, including birds and fish. Vegetarians refrain from all animal flesh. Ovo vegetarians include eggs but not dairy in their diets. Lacto vegetarians eat dairy but not eggs. Lacto-ovo vegetarians eat both. Along with animal flesh, vegans avoid dairy, eggs and often honey.

According to the Global Footprint Network, the ecological footprint “measures how fast we consume resources and generate waste, compared to how fast nature can absorb our waste and generate new resources.” The cycle of food consumption and production is a critical footprint component, measured as the number of hectares of biologically productive land and sea needed to support an individual’s or a community’s food consumption.

According to a 2006 report from the U.N. Food and Agriculture Organization, livestock cultivation, chiefly for meat production, accounts for nearly one-fifth of total worldwide greenhouse gases, the main drivers of global warming. The global meat industry pollutes more than the transportation sector, especially factory farms, often criticized also for their animal welfare violations and poor labor conditions.

According to FAO, about 2.7 percent of total worldwide greenhouse gases come from milk production. EWG identifies dairy products, except cheese, and eggs as eco-friendlier protein sources than meat. A carnivorous diet requires "2.9 times more water, 2.5 times more primary energy, 13 times more fertilizer, and 1.4 times more pesticides” than a lacto-ovo vegetarian one, according to a May 2009 study by U.S. scientists in the American Journal of Clinical Nutrition.

A May 2009 American Journal of Clinical Nutrition paper from Sweden emphasizes: “”Plant foods based on vegetables, cereals, and legumes present the lowest GHG emissions with the exception of those transported by airplanes ... Changes toward a more plant-based diet could help substantially in mitigating emissions of GHGs.” An entirely plant-based or vegan diet, especially if locally or regionally grown, thus represents the most environmentally friendly cuisine.

If you calculate your eco-impact at MyFootprint.org, your diet’s precise contribution to your result might vary, for example, with your country and your level of local, unprocessed food consumption. However, you can try a small experiment that brings home the scientific evidence regarding veganism as the most eco-friendly diet. Take the MyFootprint.org quiz several times, using all the same answers except to the question “What best describes your diet?” Each time, try a different answer choice, starting with “vegan” and ending with “top of the food chain,” Your total footprint will probably enlarge as you move down the list.

Plenty of online resources can help you reduce or eliminate meat, dairy and eggs in your diet and eat more local and organic foods. They include EWG’s Meat Eater’s Guide to Climate Change and Health, Vegetarian Times magazine, Vegetarian Resource Group, the Physicians Committee for Responsible Medicine's vegan Power Plate, and Ecology Action’s guide to high-yield organic gardening.