Only one who can learn the process of nescience and that of transcendental knowledge side by side can transcend the influence of repeated birth and death and enjoy the full blessing of immortality.
Some neophytes on the spiritual path may fall into the illusion that taking care of the body is somehow evil, or a sign of spiritual backwardness. Not only may they neglect the needs of the body, but they may go out of their way to actually damage the body. Such people actually hate the body. They see it as a source of misery, and thus they take out their anger on it. This is certainly a mistake.
Masochism can never lead to spiritual perfection. The body is actually a most precious property of the self; it enables the self to engage in various devotional activities that can bring about a change in consciousness. A person's external activities affect his consciousness, and his consciousness affects his external activities. Knowing this, a bhakti yogi consciously chooses to engage in particular external activities in order to bring about the desired spiritual happiness and wisdom.
However, neither the Sri Ishopanishad nor any other Vedic literature recommends that we neglect bodily needs. The Bhagavad-gita states:
There is no possibility of one's becoming a yogi, O Arjuna, if one eats too much, or eats too little, sleeps too much or does not sleep enough.