Does Jewish law discourage a vegetarian lifestyle? One might assume so from the fact that the Talmud states that "When the Temple was in existence, there could be no rejoicing save with meat" (Talmud Pesachim 109a) and some of the most famous Jewish culinary dishes are chicken soup, brisket and chopped liver.
The basic response to the question of vegetarianism is that, without the Temple (when there was a sacrificial service), there is no requirement for anyone to eat meat. The references to meat being essential to one's rejoicing can be understood to mean that one should serve a more exalted fare on the holidays and on Shabbat.
The question of the Jewish view on vegetarianism is not new. One can find discussions of the benefits of a vegetarian lifestyle even in Medieval scholarly works. Many Jewish scholars who advocate for vegetarianism point out that Adam and Eve were vegetarians. When God placed Adam in the Garden of Eden, the Torah tells us that God said: "Of every tree of the garden you may freely eat..." (Genesis 2:16). While God had granted Adam dominion over all creatures, only the plants were marked for human consumption.
On the other hand, advocates for the consumption of meat point out that after the Great Flood, God told Noah and his family that "Every creature that lives shall be yours to eat; like the green herb, I have given you everything. Only flesh with the life thereof, which is the blood thereof, you shall not eat" (Genesis 9:3-4).
Vegetarians most often choose to abstain from meat because (1) they do not enjoy eating meat, (2) they belief in the health benefits of a meat-free diet or (3) they feel that eating meat is cruel to animals.
For those who do not enjoy eating meat, the only challenge in Jewish life is ignoring peer pressure from those who are of the opinion that one must eat meat on Shabbat and Yom Tov. Food is meant to not only sustain us, but to be enjoyable as well, and one need not eat a food they dislike.
Those who are focused on the health benefits of eating a vegetarian diet are, in effect, following the important mitzvah of taking care of one's health. This is a mitzvah that Rabbi Moses ben Maimon (Maimonides, 12th century Spain), who was also a physician, place great importance on. It is interesting to note that The Life Transforming Diet, by David J Zulberg, a 2007 book that outlines a diet-plan based on Maimonides' principles of health, promotes a diet high in fruits, vegetables, legumes and whole grains and, therefore, low in meat.
Choosing a vegetarian diet out of concern for the pain suffered by animals also aligns with Jewish law. The Torah laws dictating the treatment of animals are known as the prohibitions of tza'ar baalei chayim - causing undo suffering to living creatures. This is why Jewish law prohibits hunting for pleasure and why the Jewish act of shechita (kosher slaughter) is meant to cause the least amount of pain to an animal.
The philosophical conflict between vegetarianism and Jewish thought occurs when the fear of hurting an animal becomes the equating of humans and animals. Traditional Jewish teachings make it clear that humans and beasts are not the same. Based on the text of Genesis, Adam (and all humans thereafter) are separated from the animals as the only creation to receive the breath of life from God. Humans are the only creatures who are expected to live according to a moral ethic. Being kind and caring to animals is important - indeed, God instructed humankind to take care of the animals and the world, but equating humans and animals lowers our expectations of ourselves.
So what about the meat eaters? It is pretty clear from the story of Noah that God gave humankind permission to be carnivores (well, omnivores, really). There are some opinions that this permission was granted because pre-flood humanity had been so strongly overwhelmed by their basest character traits that they were now so much more physical that they needed the extra nourishment provided by meat. It is interesting to note that the Malbim (Rabbi Meir Leibush, Eastern Europe, 1809-1879) suggests that the physical nature of both humankind and the world in general was altered after the flood. Not only did produce no longer supply the same level of nutrients, humans themselves were now weaker physically.
On the other hand, when God singled out the Children of Israel and assigned them the unique role of becoming a "Holy Nation," He limited their omnivorism. The types of meat/poultry/fish that they were permitted to consume was limited to the animals we now label kosher, which were deemed spiritually beneficial, or at least not spiritually polluting. Additionally, the Jewish people were taught the laws of shechita (kosher slaughter), which was considered the most merciful means of slaughter (a discussion for another piece altogether).
Whether one chooses to become a vegetarian or to eat a more omnivorous diet is an individual choice. However, Jews are food people, and there are many laws that dictate how and what we eat. Not only are there the rules of kashrut (from shechita to the separation of meat and milk and the checking of vegetables for insects), but blessings on the food both before and after one eats. In all of these laws, however, the benefits and negatives of the foods. From this it is understood that no matter what one chooses to eat, the goal should always be to nourish oneself on both physically and spiritually.