as we were told at the university - some people have a predisposition to weight gain and weight loss at the genetic level.
in this case, the body itself controls weight, when it needs to start to store, and when this stored energy is not needed - he gets rid of it.
it is easier for such people to lose weight after winter without resorting to diets - the excess will go away by itself
Hormones can be naughty. Maybe you're talking about seasonal weight changes. And maybe you do not take into account some of the actions that you perform - for example, you go to the country house and dig there, or you sit longer than usual. In a year, just sitting, I gained about 10-15 kg of weight. Before that, I often walked and the weight was within the same value - 49-54. Now the weight is 67-69. That's all.