Why Does Weight Return After Dieting? Many people lose weight quickly by severely restricting calories, only to regain it once they resume normal eating. This phenomenon, known as weight regain or the Yo-Yo Effect, is a natural biological response rather than simply a lack of willpower. What Is the Yo-Yo Effect? When calorie intake remains too low for an extended period, the body adapts by conserving energy. These adaptations include: Lower resting metabolic rate Increased hu