That is true but it also should be noted that many autistic children are just overweight. Some are not well coordinated and being active is difficult.. also some are obsessive about food and it would be difficult to control their diet (especially at 14) without riskin a HUGE tantrum and you do not want a mansized 14 YO having one of those.
When we thought my daughter had Angelmans Syndrome (still do but not enough genetics testing out there) we ran across another genetic disorder that was on the same chromosome that caused children to eat and eat and eat. I can't remember the name, but there have been publicized cases of parents having to lock the cupboards and fridge etc to keep the children from eating everything in site. I wish I could remember the disorder/syndrome...but I can't. It wasn't related to Autism at all, btw.
Travolta's son could have anything out there, and he may even be undiagnosed. Even with the best doctors and all the money in the world, nobody may truly knows what he has. Poor guy. I wish them the best.