Chanukah is difficult to do on a few calories. Unlike Purim, there is no obligation to have a seuda (festive meal) on Chanukah. It has become a custom however to have a meal which shows gratitude to G-d for the miracles that happened for the Jewish people.
One of the main miracles that happened for the Jewish people was that when the Jews recaptured the holy temple after the Greeks had defiled it, a vessel of oil was found in perfect condition with the seal of the Kohen Gadol (High Priest) still intact. Rather than lasting for one day, this oil miraculously lasted for eight days, which gave the Jewish people enough time to press more olives and have the oil delivered to the temple in Jerusalem.