A vegetarian diet is often praised for its health benefits. Studies have shown that vegetarians usually have lower levels of heart disease and a risk of diabetes（糖尿病）than people who eat meat. What most people are less aware of, however, are the effects that a vegetarian diet can have on the environment.

Researchers from the Union of Concerned Scientists in the US recently studied how consumer behavior affects the environment. The study showed that meat consumption is one of the main ways that humans can damage the environment, second only to the use of motor vehicle.

Then, how can eating meat have a negative effect on the environment? For a start, all farm animals such as cows, pigs, and sheep give off methane gas（沼气）by expelling（排出）wind from their bodies. One cow can produce up to 60 liters of methane each day. Methane gas is the second most common greenhouse gas after carbon dioxide. Many environmental experts now believe that it is more responsible for global warming than carbon dioxide. It is estimated that 25% of all methane released into the atmosphere comes from farm animals.

Another way that meat production affects the environment is through the use of water and land. 2,500 gallons of water are needed to produce one pound of beef, whereas 20 gallons of water are needed to produce one pound of wheat. One acre of farmland used for crop production can produce 40,000 pounds of potatoes, 30,000 pounds of carrots, or 50,000 pounds of tomatoes.

Many people now see the benefits of switching to a vegetarian diet, not just for health reasons, but also because it plays a vital role in protecting the environment. However, some nutritionists advise against switching to a totally strict vegetarian, or vegan diet. They believe a vegan diet,   which excludes（拒绝）all products from animal sources,   such as cheese, eggs, and milk. can be short of many necessary vitamins and minerals our bodies need.