APA Dictionary of Psychology

n. voluntarily abstaining from food. A person is considered to be fasting 8 to 12 hours after his or her previous meal, an amount of time that allows the body to digest the meal and adjust metabolism accordingly. Fasting may be undertaken in preparation for medical or research procedures; to cleanse the body for therapeutic or religious reasons, as evidenced by the popularity of many “detox diets”; or to lose weight. For weight loss, beginning a diet with a fast or a very low-calorie diet can help kick-start the process. Intermittent fasting, or regularly alternating between eating normally and fasting, may improve the body’s stress resilience by reducing spikes and troughs in blood sugar and cortisol levels. As long as one is well hydrated while fasting and is reasonably well nourished at the outset, one can fast for several days without significant or long-lasting ill effects. Pursued for too long a time, however, fasting causes the body to become malnourished and to burn muscle rather than fat; this type of unhealthy fasting, seen especially in anorexia nervosa, carries a high risk of complications and is potentially lethal.