Red Flags for Anorexia nervosa
Those who are suffering this sickness are most likely to skip meals. They tend to make excuses for not eating. They are very choosy in the food they take. They tend to choose those that are low fat and low calories. Weighing of food is also practiced.
You should also look into how long they take their food. Some would go the distance of slicing everything when the food is already tender. Others, still, goes to the extent of spitting the food and pretend that it is way too hard. When you see your friend complaining that they are fat when they are already half your size, you have to check if it is you who is too fat or her who is already very thin.