I suppose there was no definite beginning to his disease. There were only small clues (and if I had only known -- I would have done a million things differently).
I remember the first clues from this past July. I don't remember what order they came in. One clue was that he stopped having treats. That was okay. We could all probably be fine with fewer treats. Another clue was his confession that his best friend had told him he was fat. I also remember him standing in front of a mirror and looking at his love-handles. At some point during the month, he found our scale and started weighing himself. And little by little, he started talking more and more about food. He started scrutinizing every food and every menu. I didn't know this at the time, but he had also heard Grandma talking at length about her new diet. I was so surprised to hear him suggest while at his lowest weight that he should go on Weight-Watchers with Grandma.
He had a pediatrician appointment mid July. I had his doctor emphasize to him that he was the appropriate weight for his height. At this point he was about 98 lbs (4'10 1/2"). He had already lost 6 pounds from his high weight of 104 lbs. At this point I even showed him his BMI -- and that he was completely normal.