I think it might be true.  Men have more muscle mass, which generates more heat and burns more calories.  Women naturally have a slightly higher body fat than men do, and women are generally shorter, meaning they need fewer calories to maintain their weight and therefore must eat less than men in order to avoid becoming fat.  In the wild, these traits may have been advantageous in times of scarcity, but in a time of abundance, they don't seem to offer much benefit. So I think it's fair to say it's probably a bit harder for women to lose weight and avoid getting fat in the first place.  It's definitely not an excuse, and CICO still applies regardless of how much muscle mass you have or don't have, but it could be true.