If you lose 4 lbs the first week from water and then 3 the next week(still water coming off, and starting to lose more
fat rather than muscle) and 2 every week thereafter, that's 17
pounds. You could lose more, but you would be losing a higher ratio of muscle to
fat. If you're just losing the weight for the vacation and don't have plans to keep losing afterward then you could go more than 17 (keeping in mind it will make it easier to put on weight afterward, and to go over your original weight) but if you did want to continue with your
weight loss, you would probably want to start slow so that you don't get discouraged and so that you lose as much
fat weight as possible. I've read that people can easily tell that you're losing weight after 10
pounds (for me since I'm already smaller, it's more like 4 or 5
pounds) so if you lose 17
pounds, that's a lot!!! And I don't think you would need to lose more than that to feel confident and happy for your vacation. Whatever you decide, good luck!!!