Scott Alexander speculates that anorexia might be caused by a distorted metabolic set point, similar to but opposite of obesity's mechanisms. Longer summary

Scott Alexander speculates about a possible biological mechanism for anorexia nervosa, drawing parallels with obesity and the body's metabolic set point. He suggests that severe underfeating might cause the hypothalamus to become hypersensitive to leptin, leading to a distorted set point where the body thinks it's too fat even at dangerously low weights. He supports this idea with observations about anorexics' fidgeting behavior, which resembles the body's unconscious weight control mechanisms, and mentions studies showing brain lesions can cause anorexia-like symptoms. While acknowledging he's not an expert and this is speculative, Scott hopes more research will explore these connections between anorexia and metabolic set point theory. Shorter summary