But he said to them, “I have food to eat that you know nothing about.”

“food” is literally the act of eating but it came to mean that which was eaten in the current idiom of Jesus’ day in a similar manner to our “eats” or “good eating.”

Jesus, who had gone forty days and forty nights in the wilderness without food, had no problem abating the appetites of the body with the prospect of pouring out the water of life to a group of thirsty Samaritans. 

Matt 4:4  Jesus answered, “It is written: ‘Man does not live on bread alone, but on every word that comes from the mouth of God.’”