Americans define a vegetarian diet in several ways. Some vegetarians do not eat any meat products or any food made from animal labor, including milk products, eggs and honey. But most vegetarians include dairy products in their diet and many vegetarians eat eggs. Some people consider themselves partial vegetarians, because they do not eat meat or farm birds, but they do eat fish. There are many reasons people choose to be vegetarian. Some religions observe vegetarianism as part of an effort of nonviolence towards animals. Many other people have non-religious moral reasons for not eating meat. They believe that killing farm animals for food is immoral and cruel. Other vegetarians believe it is more healthful to eat a plant-based diet. And some vegetarians reject eating meat for environmental reasons. Some studies show that the industry of raising large farm animals leads to water and air pollution, land damage and climate change.