APA Dictionary of Psychology

a decrease in weight caused by limiting food intake, increasing physical activity, undergoing bariatric surgery or some drug treatments, having no appetite, or experiencing a serious illness. Intentional weight loss is usually driven by a desire to improve one’s health, appearance, or both. That desire may be informed by such factors as (a) medical advice based on current evidence about higher body weight, especially obesity, and its relation to the onset and progression of disease (e.g., diabetes mellitus, heart disease, some cancers); (b) impaired function (e.g., orthopedic pain, labored breathing) because one is higher body weight; (c) one’s internalized cultural notions of fitness, beauty, and the body ideal, as well as one’s perception of others’ disdain for violations of these notions; and (d) one’s self-image as higher body weight regardless of whether one’s body mass index confirms that assessment. Of these, the cultural and psychological factors are thought to be particularly associated with the unhealthy weight-loss behaviors (e.g., fasting, purging, engaging in excessive exercise) that are seen in some eating disorders, but such factors can be equally powerful in influencing the decision to lose weight safely and within medical guidelines.