The kid probably has a slower metabolism from his parents, but evidently if you eat less you lose weight.   There is no reason to believe this kid, or any fat for that matter, has a "slower metabolism" than anyone else. Here is why.  "slow metabolisms" have an additive impact on your resting caloric expenditure, not a multiplicative impact. And the delta is typically only 100-200 calories. That means a statistically viable fat can blame 10-15lbs, tops, on their "slow metabolism". The rest is all CICO. In other words - let's suppose this eatbeast does have a reduced caloric expenditure at rest, and weighs 707lbs. If he did not have this condition, he'd weigh 692lbs. In other words, the presence or absence of a legitimate condition is totally irrelevant. The problem is overeating.