I once knew this girl who was skinny as a rail.  She would tell me that she had to eat every couple of hours cause she would loose weight.  She married this really nice man and within a few months this nice man became a large nice man.  He would tell me that at 12 AM his wife would wake up hungry and have to make herself a meal.  One night she was just plain tired and ordered a large pizza.  He said he watched her eat the whole thing. (Back then large was X-large now) She literally wolfs down major meals every couple of hours.

I got into 4400, a sci-fi show on the USA network.  The show is about 4400 people who mysteriously disappeared over the century.  They were all returned to Earth one day from a UFO.  Each was endowed with special powers.  It is kind of like the show Heroes.  A particular episode was about a man who had the power to alter the metabolism of a human through his saliva.  This fat cat gave this man major money and marketed miracle water.  Each container had a microscopic amount of saliva from this particular 4400.  People were buying this water off the shelves.  They were losing weight quickly.  Only problem was that they had to keep eating all the time. After about a week people who drank the miracle water were dying of starvation.

I think I would like to adjust my metabolism.  But not to the extent of above examples.