Christians are becoming vegetarian for several inter-related reasons:

Vegetarian diets are excellent for health.
Many Christians choose vegetarianism for its health benefits, which have been recognized by various dietetic and other medical organizations. Vegetarians have reduced rates of heart disease, obesity, diabetes, and certain kinds of cancer.

For a review of the health advantages of a meat-free diet, see Vegetarian Diets -- Position of the ADA [American Dietetic Association]

The Physicians Committee for Responsible Medicine publishes useful resources, as does Hallelujah Acres, a Christian health ministry founded by George Malkmus.

In addition, numerous respected physicians, such as Drs. Charles Atwood, John McDougall, and Dean Ornish, and dieticians such as Mark and Virginia Messina, Brenda Davis, and Vesanto Melina, have advocated the diet.

Vegetarian diets are better for the environment.
Plant-based diets generally consume far less resources.

Christians who care about Creation will consider eating lower on the food chain, since raising animals for food contributes substantially to rainforest depletion and greenhouse gas emissions that cause global warming. Intensive animal agriculture causes water pollution, topsoil depletion, and soil degradation, while plant-based diets generally require far less resources. For more details, see GoVeg.com (see "Think You Can Be a Meat-Eating Environmentalist?), EarthSave.org, and E Magazine's cover story "So You're an Environmentalist? Why aren't you a vegetarian?" Worldwatch editor Ed Ayers' article in Time Magazine argued that environmental concerns will encourage vegetarianism in the 22nd Century.

Vegetarian diets help feed the world's hungry.
While many millions die of hunger annually and many more suffer malnutrition, worldwide one-third of all grain is fed to animals being raised for slaughter; in the U.S., the proportion is nearly three-fourths. Converting grains to meat wastes about 90% of grains' proteins, 96% of their calories, and 100% of their carbohydrates and fiber (Keith Akers, A Vegetarian Sourcebook).

Vegetarian diets spare animals from misery on today's factory farms.
Modern intensive animal agriculture commits animals to repeated and prolonged pain and suffering. Animals suffer greatly from stressful crowding, barren environments that frustrate their instinctive drives, and manipulations without anesthesia, such as debeaking chicks, cutting off pigs' tails, and castrating and branding cattle (Erik Marcus, Vegan: The New Ethics of Eating - now available as a free download in PDF format).

Farmers routinely use antibiotics to prevent infections in crowded, stressed animals, and this promotes dangerous antibiotic-resistance among bacteria. You can prevent infections by cooking meat, but this generates cancer-causing heterocyclic amines. Farmers also add hormones, harmful to human health, to stimulate excessive muscle development in animals, causing painful lameness. Slaughter typically involves terror and, often, great pain (Gail Eisnitz, Slaughterhouse).

Vegetarian diets typically feel excellent,
enhancing one's sense of well being and increasing one's exposure to a wide range of healthy, great-tasting food.

Vegetarians generally relate that they feel better. They often lose weight, and they frequently feel lighter, healthier, and sexier. Many report that their menu has broadened in new and interesting directions.

Vegetarian diets express a faith in the reconciliation of all Creation to God's original intentions.
Scripture foresees that the vegetarian diet of the Garden of Eden (Gen 1:29-30) will be restored with the coming of the Peaceable Kingdom (Isa 11:6-9; 65:17-25).

taken from christianveg.com

For more information see :

• Richard Alan Young. Is God a Vegetarian? Christianity, Vegetarianism, and Animal Rights. Chicago, Open Court, 2000. Prof. Young makes a compelling case that vegetarianism accords with God's highest ideals.
• Andrew Linzey. Animal Gospel. Louisville, Westminster John Knox, 1999. Prof. Linzey argues that reverence for God and respect for God's creation mandates respectful treatment of animals.
• Stephen H. Webb. On God and Dogs: A Christian Theology of Compassion for Animals. New York, Oxford University Press, 1998. Prof. Webb's scholarly study suggests that grace and redemption often involve loving and compassionate relationships with towards animals.
  

You can find more information on Christianity and vegetarianism at the Christian Vegetarian Association