I think vacation weight gain varies. I remember going to Club Med in 1989. I only had one outfit that was comfortable enough to wear on the plane home. I gained 9 lbs in one week, but, a lot of it was salt because they use so much canned and prepared foods. I gained about 7 on my Millennium Cruise and had a lot of swelling because of the sodium in the food on that cruise.
I never use salt so when I eat stuff like that it affects me terribly. I do not notice the same problem on the RSSC ships, maybe, because they use more fresh stuff. I also think that the alcohol also is a causitive factor in the weight stuff, although when I went to the Club Meds they were all sober vacation weeks and there was no drinking (my ex-husband could not drink).

Tahiti will be good - all the fresh fruit and fish sound really good to me. The desserts and drinking are where things sneak up. Oh and full breakfasts too.