"Sex and Bread" joke

Two older men are sitting on a park bench talking and one of them asks the other about his sex life. The man answers that he has an excellent sex life and is still very active.

The other man confesses that his sexual appetite has greatly diminished with old age so he asks the other man if he has any secrets for staying sexually vital.

"Well," answered the man, "I eat rye bread everyday. That is my secret. If you just eat rye bread, your sex life will improve dramatically."

The other man decides to follow this advice and finds a bakery nearby. He tells the clerk behind the counter that he wants all of the loaves of rye bread that they have in stock.

The clerk then asks the man, "do you want whole loaves or do you want us to slice them?"

The man looks puzzled and asks the clerk, "what is the difference?"

The clerk responds, "Well when it's sliced, it gets harder faster."

To which the man responded, "How come everyone knew about this but me?"