From the website of the International Vegetarian Union
Interestingly, there are several Catholic Monastic orders (the Seventh Day Adventists being Protestant) that are vegetarian.
The vegetarianism of Francis of Assisi, of St. Martin de Porres, of St. John Chrysostom is written of by biographers. Vegetarian Catholic orders include the original Benedictines, Cistercians, Trappists, Carmelites and Franciscans, whose founder believed that plants too have feelings.
Amongst the Benedictine monks, Frenchman Father Henri Le Saux (1910-1973) and English Benedictine Dom Bede Griffiths (1906-1993) founded Benedictine monasteries in India. They were strict vegetarians absorbing into their order the concept of the ashram and sannyas. They both wore saffron and adopted Sanskrit names.
Osage Monastery, a foundation of the Benedictine Sisters of Perpetual Adoration are also vegetarian.
Notable amongst the Trappist Monks, Thomas Merton was outspoken in advocating vegetarainsm.
Trappist and Carmelite orders are particulary frugal with their diet (and speech) regarding any kind of rich food to be nonconducive to meditation. "the wisdom behind using vegetarian food is that it is not conducive to lust and not provocative to the flesh."
"The Essenes were one of the three main religious sects in first century Palestine and Jesus is believed to have been a member of the northern group, centred around Mount Carmel. The Essenes were also known as Nazarenes. Members of the sect wore white and followed a vegetarian diet, as do the Carmelite order of Christian (Roman Catholic) monastics, it is interesting to note that current members of that order based at Mount Carmel openly claim that Jesus was an Essene and was raised on Mount Carmel, even though the Essene scriptures are excluded from the Bible as generally promulgated by the Church.
The main Essene scripture is the Gospel of the Holy Twelve, rediscovered in 1888 and translated from the Aramaic by Rev. Gideon Jasper Ouseley. This version of the New Testament differs markedly from those generally accepted in that it portrays Jesus as a strict vegetarian:
"Before all things is love, love ye one another and all the creatures of God, and by this shall all men know that ye are my disciples."