Albert Barnes Commentary 1 Kings 19:8

"And he arose, and did eat and drink, and went in the strength of that food forty days and forty nights unto Horeb the mount of God." — 1 Kings 19:8 (ASV)

Older commentators generally understood this to mean that Elijah had no other food at all, and they compared this long fast with that of Moses and of our Lord (see the cross-references). But the words do not exclude the possibility that the prophet obtained such nourishment from roots and fruits as the desert offers to a wanderer, though these alone would not have sustained him.