Although I have been prevented by outward circumstances from observing a strictly vegetarian diet, I have long been an adherent to the cause in principle. Besides agreeing with the aims of vegetarianism for aesthetic and moral reasons, it is my view that a vegetarian manner of living by its purely physical effect on the human temperament would most beneficially influence the lot of mankind.
Letter to to Hermann Huth, December 27, 1930. The Ultimate Quotable Einstein (ed. Princeton University Press, 2010), p. 453 - ISBN: 9781400835966