This. Every year when leave the boat for 4-6 weeks to visit family, we gain 10lbs. Once back on the boat in our normal life, we lose it and easily maintain our previous weights. After several years of this, we have definitely fingered snacking and huge portions of rich food as the culprit. We aren't fitness freaks, and don't watch or limit our eating in any way, and often eat things that aren't nutritious - but when we return to the US, we are always floored by how much everyone eats. We can split meals in some restaurants and still have food left over. Some of the burritos served in Mexican restaurants are larger than frisbees. Everything is shoved full of cheese and cured meats, and everyone is grabbing boxes and bags of snacks in between meals. The TV seems to be nothing but advertisements for unhealthy food and fast food restaurants, interspersed with diet foods/drugs and weight-loss programs. I do, however, prefer these advertisements over the scheduled programming - which seems to mostly consist of people screaming at each other, the audience, and the viewers.
Most of the people we meet out cruising are of moderate weight - not skinny, but not fat - and unconcerned with diet. A common conversation after someone visits the US is disbelief on how much food people eat there and how much time they spend thinking about food.
Mark