In the Torah reading of Yom Kippur we are told TE’ANU ET NAFSHOTECHEM, “…you shall afflict your souls…”. (Lev. 16,29) It is well known that “affliction” here refers to the restrictions of Yom Kippur: the prohibitions of eating and drinking, of washing, of anointing, of wearing shoes, and of having marital relations. (There is a difference of opinions among the Rabbis as to which of these prohibitions are Biblical and which are rabbinic.)
Rashi in the Talmud adds another prohibition not enumerated here, preparing salad in the afternoon to be eaten after the fast. (Shab. 114b) Coming in contact with food and avoiding eating it is another form of affliction.
Rabbi Soloveitchik told a story about one of the wealthy Rothschilds who was observant and one year had a traveling Rabbi spend Yom Kippur with him. During the break in services after Musaf the guest was taken home and was surprised when he arrived there to find the table set with delicious food. The guest was shocked when he saw his host go over to the table, pick up a bottle of wine, and start pouring it into the Kiddush cup.
He then picked up the cup and started to recite: Master of the Universe, before we eat we should make Kiddush. Since today is Yom Kippur and we are forbidden to eat and drink so as to afflict our soul, we will avoid eating and drinking and return to the synagogue to continue with our prayers.
His actions demonstrated the will power to avoid temptation and subdue his bodily desires in keeping with the Biblical directives.