It continues to distress me that people think the brain doesn't need food, or a minimal amount will do, or that you can just opt out of certain foods or nutrient groups and your brain will make do.
It is still unclear how much of an eating disorder precedes and how much is the result of restrictive eating, but this is clear: the brain is horribly damaged by malnutrition and erratic nutrition. Purging and restricting and bingeing do damage to the function and learning and structure of the brain. And you don't have to be "underweight" on some chart or visibly unwell. Anyone who is working to stay at or avoid a level of nutrition that the body resists is at risk.