People are mean and they throw proverbial daggers to others, often during their youth, that ultimately distorts their perception to point the brain itself starts misperceiving things. So, an anorexic will not see themselves as thin or even think their are still fat despite going under 90 pounds.
On visceral level, an eating disorder is a perversion of pursuing reproductive fitness. The girl/woman believes she is pursing physical attractiveness with lower weight while the boy/man believe getting extremely "jacked" will make him attractive. Food is not the only way disordered thinking happens. Some cultures value big butts, and thus people keep getting illegal injections so their ass grows larger but remain unsatisfied in aeternam.
Fat and meat has been so unfairly demonized it’s kind of pathetic. When a disordered individual comes across such information, they go to the "solace" of carbohydrate-only foods. Vegetables and fruits are mostly cool, but it also means white bread, white rice, etc are deemed safe and healthy to eat with impunity. Well, newsflash. Hormones affect hunger and the rise and fall of insulin creates a reliable cycle of hunger.
Food industry makes bucks from sales and carbohydrates from flour and other sources gets people to eat more in many ways. They toss some B1 and B2 vitamins in wheat flour-based products so no overt crisis manifests itself from constant, repetitive starch eating.
Some of the factors of health are matters that are asymptomatic and not visually noticeable or indicated by muscle size or figure, which is predominantly a protein and work matter. Bones are asymptomatic matter where the necessary vitamin and minerals needs to be consumed constantly.
Girls are more sympathetic characters on a visceral level too. The pass down the species and and usually have to bare the responsibility of raising the offspring. thus need the best male. Whereas males are a commodity and one that drops out of the pool can simply be replaced by another.
Last thing, I find it interesting that the article mentions that the lanky nerd build is somehow desirable....