If you are EXTREMELY overweight (like 300 lbs +) and start eating right and working out how much weight can?

you lose in a week? Don't you lose a lot of weight initially? I am asking because on the biggest loser, or any weight loss show the contestants seem to lose huge amounts of weight in one week their first week. (sometimes 40 lbs I have seen). I know they work out hours a day but would a person working out normally who was that heavy still lose a ton of weight right away or is that just completely exaggerated for tv?