Honestly none of that makes any sense. Because even if being fat allowed you to mature faster and pass on your genes quicker, you would not be able to run fast enough to keep up with your potential mates. Unless the individual was able to somehow keep their sperm in a chilled storage unit of some kind, there is no way that they would ever be able to deliver on that promise. So, evolutionarily speaking, they would likely not be able to protect any children they had from mountain lions. It is more likely the case that the corellation between BMI and reproductive success came about during the Ice Age, when it was very cold and extra layers of fat were needed to survive the winter.