AnswersIs Weight Naturally Cyclical?
From an evolutionary standpoint, it would make sense for hormones to direct the body to store more fat before winter. It was even more difficult to find food in the winter in most regions, so the genes that survived through the generations were the ones successful at storing enough extra energy in the late fall to ensure that the body would be able to survive long periods of little or no food.
But your issue appears to be opposite this logic. You gain in the summer and lose in the winter. It could just be the way you're built. Everyone is a little different, and the hormones of one person can differ greatly from the hormones of other people.