Okay, I'm jumping in the conversation without having red all the posts (so it was maybe said earlier, sorry if it was) but here's what I think :
I think they probably do have some nutrition mentoring or something, but that they just don't show it for the ''marketing'' reason.
I mean, general population probably prefer watching show for the drama/effort of the training (will they succeed? will they fail?) and not ''you should eat carrot and not french fries''.