The Or Hachaim, Rabbi Chaim Ben Attar, In his Commentary on Bereshis (Genesis) 18:4 explains "Bread Symbolizes the Depths (Pnimiut) of the Torah... Bread Nourishes the Body and Soul."
If prepared correctly, bread has the potential to be food for the soul. In this commentary, the Or Hachaim talks about water and bread: water symbolizing the pshat (simple meaning) of the Torah and Bread symbolizing the depths (pnimiut) of the Torah.
In the following verse, the Or Hachaim asks why did Abraham invite the angels to dine with him? Angels don't need to eat! The Or Hachaim answers that food has spiritual secrets. As it says in Proverbs 18:25 "The righteous eat to satisfy their souls." To satisfy the soul means to enhance the Ruchniut- the spiritual side of a person.