It must be true. In my 20's when I weighted 98 pounds, I wore a size 0 jeans. Now that I'm 10 pounds heavier I still wear a size 0 Jeans. But something to consider is the fabric the garment is made from. 100% cotton is going to be tighter than cotton mixed with stretchy fabric such as lycra, polyester, spandex, etc. That may very well be the reason for the perceived differences between jeans of the same size.