The bulk of this pleasant if disjointed book is a medical explanation of fasting, offered with a studied prudence which contrasts oddly with the interspersed testimonials by veteran and novice fasters. Ross, whose own ignorant enthusiasm resulted in one youthful brush with disaster, is extremely conscientious about recognizing the dangers of fasting. Food deprivation for more than three days causes a massive somatic readjustment designed to conserve the body's remaining resources by a switch from ordinary glucose metabolism to ""catabolism"" of its own stored fat and protein reserves. According to Ross, some of the functions of glucose are taken over by ketone bodies, which keep most vital processes running at a slower pace but have two important side effects: build-up of acid in the body resulting in electrolyte imbalance and a reduction in the level of oxygen available for brain functions. Unlike diabetic acidosis, fasting acidosis can be maintained with relative stability over a long period of time, but Ross emphasizes that it should be risked only by healthy adults under a doctor's care and with a clear idea of what they're getting into. The first-person accounts tend toward euphoria (""There are times when you are fasting, if you stand up quickly, it's absolutely a space."") The virtues most frequently celebrated are the rapid weight loss, the drugless high (probably caused by lowered brain oxygen), and--most interestingly--the greater awareness of food as a chemical and sensory experience. On the whole, a modest, responsible treatment.