Given that Eli is supposed to be growing up a bit due to the plot and his circumstances, I think it would have been a smart and interesting idea to help the actor lose some weight and have Eli's development mirror a growing adult self confidence.
He's the only one who is a possible second for Rush so would end up being a pretty critical team member in time. (We already see that for all Rush is annoyed at moments with dealing with a "kid", he tacitly admits Eli really does have a brain and that he needs him.)
Um, the actor has lost loads of weight since season 1, he mentions it in a few interviews.
