From a Traditional Chinese Medicine perspective:
Brahmins, who did not engage in battle, but focused on study and spiritual development, were forbidden use of meat. This brings up the next point on meat eating, and how it effects us spiritually. This view is both disturbing and confusing. For, what these authors seem to be saying is that for ideal spiritual development one should eat as a vegetarian , but for most of us with little hope anyway, this is not appropriate. Perhaps this is a bit facetious, but in examining the energetic qualities in meat, it is not held in high regard by Taoists, and it would seem something of a necessary evil for those of us living in modern culture.
There is the psychological energetic aspect to this subject which follows that eating meat creates many disturbing desires. Those who consume meat are filling themselves with low energy foods producing a gross spirit producing animalistic tendencies and belligerent mentalities. On the other hand those who eat more vegetables will supposedly have a more harmonious spirit. As Hua Ching Ni recommends:
"The highest beings absorb pure energy...People trying to spiritualize their life eat only light subtle foods such as herbs and vegetables."
Pitchford notes that just as certain animals have certain attributes which may be beneficial to health, they also have negative attributes which are transmitted to the eater. The shyness of the rabbit or the desires of the pig are examples of this. He further argues that perhaps much of the stress that is attributed to a modern lifestyle may be the result of eating too much meat and its toxic by-products, obstructing the body's physical and therefore mental well being.
Though most caution against the practice of a strict vegetarian lifestyle, the practice of including meat in the diet is approached with caution among modern Taoist authors. Meat should represent only a fraction of the total diet. Eating too much meat in the diet creates a condition of Yin blood, or an acidic imbalance leading a person to become prone to illness. On the other hand a strict vegetarian diet may cause one to become too alkaline. A harmonious balance should be sought for. Maoshing Ni in The Tao of Nutrition recommends gradually moving to a mostly vegetarian diet, including meat as no more than 1/10 of all food consumed.
As practitioners of Oriental Medicine it behooves us to remember that we are instruments of influencing body, mind and spirit. In our Western materialistic society it is often easy for us to focus on ailments of the body, ignoring the rest. We need to be sensitive and understanding of others who are seeking a more spiritual existence, and be prepared to work with them within the parameters of the lifestyle choices of others. In our own tradition there are precedents for including at least a little meat in the diet. There is also a tradition for forgoing this for spiritual purposes. If a patient who has chosen a vegetarian lifestyle is having health difficulties, assessment of their particular regime, and alterations to the diet can be made. This should be attempted and encourage first, before insisting that meat should be eaten. According to our own tradition meat should only be a very small part of the diet anyway. If it appears that meat is, in our opinion, absolutely necessary, we must be prepared to counsel patients and provide them with a very clear understanding of their health and allow them to make an informed decision. This strategy should be approached with knowledge and compassion for our vegetarian patients.
http://acupuncture.com/nutrition/vegdiet.htm