“…People with anorexia nervosa (AN) enter a vicious cycle, whereby malnutrition and weight loss drive the desire for further restricted eating and emaciation”
Why might that be?
“Evidence suggests that, compared with healthy individuals: individuals who are vulnerable to developing an eating disorder might have a trait [prior to eating disorder onset] for increased extracellular serotonin (5‑HT) concentrations and [a different ratio] in postsynaptic 5‑HT 1A and 5‑HT 2A receptor activity”. These two changes, together “might contribute to increased satiety and an anxious, harm‑avoidant temperament”
In other words, the biological drive for anorexia is related to an elevation of serotonin.
Thus, the most supportive meal program for anorexia is one that is heavier on fats and protein and lower in carbs. This is recommended to both get enough energy to function hormonally. but also to cater for the natural tendency to react strongly to any serotonin triggers. A high carb diet type would typically drive up the serotonin and thus worsening the anxiety at a biochemical level for someone struggling with anorexia.
In short: Eat more fat if you are an anorexic in recovery.
Do not rely on low-fat carby snacks - that will tend to make you feel worse.
Reference: Kaye, W., Fudge, J., & Paulus, M. (2009). New insights into symptoms and neurocircuit function of anorexia nervosa Nature Reviews Neuroscience, 10 (8)