Body fat makes a difference with how you get chilled when you stop for sure. When I was in really good racing form I froze if the made us sit at the start or if I stopped and didn't have a layer to put on. While riding hard I put out heat like a furnace fat, skinny, or in between. Also I know fat people who get cold really easily even in fairly warm conditions due to poor circulation. So the fat keeping you warm thing isn't all that straight forward. It may or it may not.