SWAPPING: A Russian and a Jew

A Russian and a Jew found themselves together in the same compartment in a train traveling to Vladivostok and engaged in a conversation shortly after. Soon it was lunchtime. The Russian took out some chicken which he ate with bread, while the Jew took out some sardines and also ate it with bread.  
“Tell me something, Anatoly, "the Russian said, with a mouthful, “How comes you Jews are so clever?”
“How do you expect me to explain it,” replied the Jew.
“With a simple analogy. Our lunch for example,” Mikhail replied.
“Perfect! Now you are eating chicken and I'm having sardines. Sardines are fish, and studies say fish contains phosphorus; and phosphorus improves the brain . . .”
The Russian thought about it for a moment and then said to the Jew, “How about us swapping what is left of our lunch?'
“No problem,” the Jew offered and went with the idea.
The Jew finished what was left of the chicken as if he had a deep craving for it, and then watched the Russian with a curious look on his face as he  munched the sardines.
“Well, now what?” The Russian said in  grumpy voice, “the sardines did me no good. I am still hungry.”
“Ah-ha! Exclaimed the Jew, “Now, you see what I mean. It is working already!'