Indeed, the format of the show is very unrealistic. They work out for 6 hours a day with very little food. That is why they drop a lot of weight in a week, especially in the first week. There is another show on ABC, entitled Extreme Makeover: Weight Loss Edition, in which the depictions of weight loss are much more realistic, with the only difference being the presence of cameras to document the progress.

I also found out that the antithesis of The Biggest Loser is a show entitled Man vs. Food, which aired from 2006 to 2010 on the Travel Channel, and featured a man named Adam Richman overindulging and participating in various mass quantity and/or extremely piquant (spicy) eating challenges.

Going back to weight loss, I've seen infomercials for exercise programs that these obese contestants are better off doing. P90X and Insanity are pretty extreme workouts, but even those are still somewhat more realistic than being on The Biggest Loser.