Spiritual seekers have tried many different approaches to deal with the issues of the physical body. As a result, there is an extensive body of experience from which to draw conclusions. Western anatomy and physiology, studies in the field of biology also have approached the issues of the physical body and can provide relevant further details.
Fasting is a part of many disciplines and those who practice it have found an increased sense of mental clarity and a heightened vital energy at various times. When taken to extremes, however, the body tends to waste away and becomes less able to carry the practice forward. There is an interesting anecdote about Tibet’s great yogi, Milarepa. Generally, it goes as follows: After a lengthy period of preparation, Milarepa was eventually given his spiritual initiation and asked to meditate. He was so engrossed in this work that he gave up eating a nutritious diet and survived on nettles for a time. At a certain point he saw his spiritual progress come to a halt and he referred to a note provided by his Guru to be read in an extreme emergency. The Guru advised that in order to go further, he would need to reinvigorate the body with nourishment! He followed his Guru’s advice and achieved the realization he sought.
We know now what the physical body requires, for the most part, in the way of nourishment in order to maintain its substance and provide a sound foundation for the intellectual, emotional and spiritual practices that human beings undertake to develop. Thus, we can work to provide this basis without falling into the extremes of either neglect or indulgence of the body. Long term, we can expect that the supramental consciousness will bring with it potentially new ways of responding to the universal energy and potentially new ways of receiving physical sustenance. We know already that plants build material substance through the conversion of the sun’s energy and the use of minerals, soil nutrients, air and water. So we know that such things are possible. Only time will tell what the solution or solutions turn out to be to liberate those undertaking spiritual development from the bondage to the body’s need for food and all that is thereby entailed.
Sri Aurobindo writes: “It is indeed possible even while fasting for very long periods to maintain the full energies and activities of the soul and mind and life, even those of the body, to remain wakeful but concentrated in Yoga all the time, or to think deeply and write day and night, to dispense with sleep, to walk eight hours a day, maintaining all these activities separately or together, and not feel any loss of strength, any fatigue, any kind of failure or decadence. At the end of the fast one can even resume at once taking the normal or even a greater than the normal amount of nourishment without any transition or precaution such as medical science enjoins, as if both the complete fasting and the feasting were natural conditions, alternating by an immediate and easy passage from one to the other, of a body already trained by a sort of initial transformation to be an instrument of the powers and activities of Yoga. But one thing one does not escape and that is the wasting of the material tissues of the body, its flesh and substance. Conceivably, if a practicable way and means could only be found, this last invincible obstacle too might be overcome and the body maintained by an interchange of its forces with the forces of material Nature, giving to her her need from the individual and taking from her directly the sustaining energies of her universal existence. Conceivably, one might rediscover and re-establish at the summit of the evolution of life the phenomenon we see at its base, the power to draw from all around it the means of sustenance and self-renewal. Or else the evolved being might acquire the greater power to draw down those means from above rather than draw them up or pull them in from the environment around, all about it and below it. But until something like this is achieved or made possible we have to go back to food and the established material forces of Nature.”
Sri Aurobindo, The Mind of Light, The Divine Body, pg. 51