Answer to Question 1
Physiologically, weight is maintained around weight set points, which are fixed or small ranges in weight. Weight regulation around set points results from the interplay between behavior, peripheral physiological activity, and central physiological activity. The process works like a thermostat to regulate the heating and cooling of air temperature near a given setting. If weight declines, hunger increases and food consumption goes up. There is a slowing of the metabolic rate and movement toward hyperlipogenesis. These reactions have obvious survival value and are likely products of evolution. The body does not distinguish between intentional attempts to lose weight and potential starvation.
Answer to Question 2
The most obvious and most dangerous symptom is significantly low weight. While DSM-5 has no formal cutoff, the average victim is 25 to 30 percent below normal body weight. The second defining characteristic is an intense fear of gaining weight. This fear is not assuaged by weight loss. In fact, the fear may grow more intense as the individual loses more weight. The final defining symptom is a disturbance in how weight or shape is experienced. Many individuals with eating disorders tend to deny that they have any problem at all with weight. Other symptoms, including amenorrhea, medical complications, and comorbid psychological disorders may be present in an individual suffering from anorexia as well.
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Mottled Sea Star (Evasterias troschelii) eating a clam, Alaska.