First I want to say that Carnival cruise line is fantastic at dealing with special diets! They smoothly handled my gluten free requests, with no complaint and with delicious results. I had lamb, cheesecake, grilled red snapper, creme brulee', chocolate melting cake (extremely decadent), prime rib that melted in my mouth. They provided gluten free bread that was pretty good. Every evening, just before dessert, the hostess would bring me the next night's menu and I could choose whatever I wanted and they would make it gluten free. I don't know if other cruise lines are so accomodating, but Carnival certainly is.
We ate in the dining room for dinner, but used the buffet for breakfast and lunch. I could find enough to eat there without consuming gluten so that worked out, too. We kind of got overwhelmed by all the eating, so by the last day we were eating ice cream for lunch and nothing else. Compund that with climbing stairs I came home a couple of pounds lighter. We only used the elevator if Grandma and Irene were with us. You don't have to gain 20 pounds on a cruise ship. I did see some people eating enough for three, but I think they were the exception. There was fruit and vegetables, salads, yogurt, and other low calorie snacks that one could eat if you wanted to eat lean.