Prolonged very low calorie diets can cause physiological changes that may cause the body to adapt to the calorie restriction and therefore prevent further weight loss.  Intermittent fasting attempts to address this problem by cycling between a low calorie level for a brief time followed by normal eating, which may prevent these adaptations. However, research does not consistently show that intermittent fasting is superior to continuous low calorie diets for weight loss efficiency.
If these extended periods without delicious food sound too painful to handle, rest assured: The best available evidence indicates that a regular ol’ diet is at least as safe and healthy and efficacious as intermittent fasting. Besides, sooner or later, a shiny new fad is bound to come along for the A-listers to fawn over, she says: “There’s going to be a new darling of the month before you know it.”
Fasting has been found to have positive effects on body mass as well as other health markers in professional athletes. This is because, as previously mentioned, fasting can effectively shed excess fat, while optimizing muscle growth, because of HGH production. Traditionally, athletes are advised to consume high-quality protein half hour after finishing their workouts (post-workout nutrition) to simultaneously build muscle and reduce fat. Fasting is advised for training days, while eating is encouraged on game days.
César Chávez undertook a number of spiritual fasts, including a 25-day fast in 1968 promoting the principle of nonviolence, and a fast of 'thanksgiving and hope' to prepare for pre-arranged civil disobedience by farm workers. Chávez regarded a spiritual fast as "a personal spiritual transformation". Other progressive campaigns have adopted the tactic.
In a physiological context, fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal. Several metabolic adjustments occur during fasting. Some diagnostic tests are used to determine a fasting state. For example, a person is assumed to be fasting once 8–12 hours have elapsed since the last meal. Metabolic changes of the fasting state begin after absorption of a meal (typically 3–5 hours after eating).