^ I gotta agree, here. I'm petite (5 feet tall), and let me tell you... it does NOT take much to appear as if there has been some drastic change. There's not a lot of wiggle room. Right now, I weigh something like 105 pounds, and I'm a little on the curvy side. If I drop ten pounds, I look emaciated. If I gain ten pounds, I look overweight. Heck, five pounds in any one direction is noticeable. We're talking a week of either the stomach flu or holiday season style binge eating, here. The first one makes me look as though I've been starving myself for ages. The second one makes me look like a pig out at the doughnut shop every morning. SMG is very petite, too, so I doubt she has much wiggle room, either.
I think Sarah's weight change probably had to do with her staying in-shape in order to meet the physical demands of the show, which would be considerable to say the least. She looked awesome whenever they showed her pummeling things in the training room. Her arm muscles were soooo cool looking. I was jealous. I wish I could have arms like that... only without the necessity of weight lifting and punching-bag pummeling, naturally. 🙂 Although, to be fair, all of this crutching around is really doing wonders for my upper body strength...