Norma Stitz, has the world's biggest natural boobs...Breasts get fat...In your 20s, your boobs are made up of fat, milk glands and collagen -- the connective tissue that keeps them firm. But as you age, the glands and collagen shrink and are replaced by more and more fat. Instead of making your bra size go up, however, the added flab can send breasts down, closer to the floor, if you catch our drift.