If you haven’t gained at least three kilos over the course of winter and can still (comfortably) fit into your skinny jeans, we’re not jealous of you one bit.But really, many of us have put on a bit of weight over winter and while we could attribute that to those extra few bowls of creamy carbonara on a regular basis, there are actually a few other fascinating scientific and evolutionary reasons why we tend to gain weight in the cooler months.