It might also be worth mentioning that grapefruit is usually banned when you are taking certain medications. That includes some contraceptive pills. I'm not sure how exactly, but grapefruit interferes with the ability of the pill to work, so if you eat it accidentally you are supposed to be aware that you aren't protected for a couple of days.
I just thought I'd mention it, because I always thought it was kind of strange and most people don't seem to know about it.
Maybe it is the same enzyme that makes you lose weight that interferes with the medication.
I really don't like grapefruit, so it doesn't matter how much weight I would lose, I just won't eat it.