Can I Lose 40 Pounds in a Month!?!?

Its not whether its believable or not.. its the genuine fact that it is not healthy at all!!!! Healthy weight loss is 1-2 pounds per week. I'm assuming the person who did this was like 500 pounds and a total carb junkie. I could definitely see someone that big losing 40ish pounds in a month. Its not healthy though. Its definitely bound to creep back up on you.