I love that show.

They literally work out 6 plus hours a day. The food they are supplied is done by a nutritionist and they are taught how to eat healthy.

Plus they have a top LA doc that monitors them and he is good. So if they have any problems like diabetes or thryoid they are monitored and treated and that helps significantly.

Plus with such a large anount to lose they can pout up big numbers, But the more close to normal they get the numbers decrease.