It is not enough to eat sparingly: he must also eat consistently, if he would keep well. He should not eat rightly for several months or years and then suddenly plunge into wrong eating for a while. For then he may lose in a few days or weeks the good health he has gained, so powerful may the reaction be. To stay faithful to his regular regime in diet is one of the basic rules he must follow. Yet friends and relatives may insist on such a departure from what experience has taught him is best for his own body and mind, and he will need much strength of will to resist them. It will require from him an obstinate adherence to his initial resolve that nothing and no one may be allowed to make him break it.
-- Perspectives > Chapter 5: The Body > # 14