In the religious and medical traditions of Asia, the human person was said to have three sources of energy: sexual, breath, and spirit. Sexual energy is what you spend during sexual intercourse. Breath energy is the kind of energy you spend when you talk too much and breathe too little. Spirit energy is energy that you spend when you worry too much, and do not sleep well. If you spend these three sources of energy, your body is not strong enough for the realization of the Way and a deep penetration into reality. Buddhist monks observe celibacy, not because of moral admonition, but for conservation of energy.
(Thich Nhat Hanh, ‘Being Peace’, Parallax Press, Berkeley, CA, 1987, p.100-101)