As a person who once weighed over 300 lbs. and am now 140 lbs lighter, I still have issues with excess skin on my back, but I found some shape wear that seams to smooth it out and you would never know, so I really believe that they have them wear some really high end shape wear to make them look even better.
Surgery is not actually allowed for the biggest loser contestants during the show. They actually need to work hard for them to lose the much needed weight. They need to engage in activities that will in the effect help them burn more fat and calories.
I lost 117 lbs, so I have had the same question. It's not about gastric bypass or lipo; it's about removing excess skin. It isn't "the Hollywood way" nor cheating. Anyone losing 100+ lbs will have lots of excess skin. It doesn't just snap back like elastic. Blow up a balloon as big as it can go, wait a while, then let the air out. It won't return to its original size and shape. Neither does human skin.
There's always a huge gap of time between the last day on the ranch and the season finale. They use the gap to continue losing, and the more they lose, the more loose skin they'll have. But other than some arm flab, I never see much extra skin in the finale. Nothing like the bat wings I'm sporting. I see no big belly aprons stuffed into those skin tight bike shorts. Something doesn't add up! So are they wearing ultra strong shapewear, or did they use some of the gap time to recover from skin surgery?
I think the latter, but why would the producers keep it secret? Like I said, it isn't cheating. Most skin surgery only takes off 5-10 pounds. Those folks have to literally work their butts off to even warrant having skin surgery. No one gets to that point by any kind of cheating.