You don't seem to have this weight problem all the time, so consider what it could be that makes the difference. Perhaps you should avoid taking holidays where you have difficulties keeping your weight down. My patients seem to have most problems when they take boating holidays or cottage holidays. Both involve sitting still for long periods and eating, especially when it rains.
With regard to your weight the same principles apply on holidays as they do at home: avoid having easy access to unnecessary food, eat only when you are hungry and don't leave snacks around. Choose plenty of vegetables, fish, lean meat and very little fat.
The holidays which my patients manage best are those which are arranged for weight reduction. But the important thing is that the holiday is mainly concerned with events and not with food.
Hotel buffet breakfasts can be a disaster for those with weight problems and it may be best for them to avoid breakfast and eat some fruit in their room instead.
Nearly all restaurants can provide a salad instead of the usual lunch menu, and one meal a day can be exchanged for melon and strawberries, etc.
Full board can be an even worse disaster if you live at a place where meals are not arranged for people with weight problems. Buffet service can cut both ways. Some people can't resist the temptation to eat far too much, whereas others choose from the bowls of salads and vegetables, get a satisfying meal and avoid gaining weight.
If food is not included in the price of the journey, and you eat at restaurants, you can order the food you need.
With skiing holidays, you often live in a cottage and eat many sandwiches both at breakfast and at packed lunches. Many people think that after a lot of hard exercise they can eat as much as they want without gaining weight. They overestimate the number of extra calories required.
If you have gone up 4 kilos, it means that you have eaten 28,000 calories too much during your holiday week and this can easily happen if you eat sandwiches, cakes and chocolate.
Here is a true story: One of my patients went on a cottage holiday for 2 weeks. As usual, I asked her to keep a daily diary detailing everything she ate. On her return I looked at the diary. The first week was very good, but the second week was really bad food-wise. I thought that something very unfortunate must have happened during the holiday which caused her to eat too much, so I asked her and she replied: "I ran out of knitting wool!"
So, make sure that you have something to do in the evenings.