I'm fairly sure it doesn't happen real fast. Your best bet is to just not eat anything. As days pass, and action mounts, the weight comes off. It doesn't take that long to lose it. So, its definitely worth putting on weight for things such as the demon door.
theres no really fast way to lose weight. starting from obese, itll take about 2 hrs to go to slim. also, u have to not overeat, which means not eating when ur health bar is already full
[QUOTE=smithrd3512]Also swinging a real heavy weapon and lots of running helps with the weight loss too. Shame theres no Weight loss program in the game....[/QUOTE]
It actually would be an interesting feature to see in a sequal - physical trainer types. Likewise, I really wish there had been some scar treatment services....
But, anyway, get into a lot of combat situations or run around a lot, and eventually the weight will come off.