They have to simply take only the necessities. Some of the yogis, I have seen, there was one yogi in Calcutta... Of course, in a temple, in a sanctified place. He was taking once only a little quantity of rice boiled with water, at three o'clock in the afternoon he was taking. That was his food and nothing more. Nothing more.
So nātyaśnatas tu yogo 'sti na caikāntam anaśnataḥ na cāti svapna-śīlasya. "If anyone dreams very much, he cannot also execute." Now, here Śrī Kṛṣṇa does not say that there is dreamless sleep. Dreamless sleep cannot be possible. It is not possible. If somebody says, "dreamless sleep," it is also another lunacy. No. Dream there must be, more or less. As soon as you go asleep, oh, dream there must be. That may be good dream, bad dream, or for long time or for little time. But dream there must be. Now, Kṛṣṇa says that na ca ati svapna-śīlasya. That means "One who dreams very much while sleeping, he cannot execute yoga."