1: Acting weird at mealtime
E.g: eating a lot, then scurrying off to a washroom, skipping meals regularly, eating alone in private, et cetera.
2: Obsessed with weight and/or body image
E.g: talking a lot about their weight, jealousy of "thin people", taking their weight measurments/BMI a lot.
3: Fixation on burning calories by any means necessary
E.g: Abuse of supplements, purging food, using a lot of unecessary laxatives and weight loss pills, exercising ad nauseum, the list goes on.
4: Extreme loss/gain of weight/body fat.
I don't think this one needs examples.
If you think you may have an eating disorder, contact a doctor.