The bible said he fasted 40 days and 40 nights. It does **not **say in what manner he fasted. It doesn’t say one way or the other what he ate or didn’t eat, drank or didn’t drink.
So your “bible only” friend is trying to make the bible say something it doesn’t say.
We can infer that Jesus didn’t eat anything, but we don’t know that.
John the Baptist went out into the desert eating only locust and wild honey-- not “nothing.”
This may be your friend’s definition, but that is NOT explicitly stated in the bible and your friend (or you, whoever came up with this “definition”) did not note that the dictionary defines fasting as both:
1 : to abstain from food
2 : to eat sparingly or abstain from some foods
What notion of him eating bread and fish? The Church doesn’t teach that, and that is not why we abstain from meat on Fridays. You are confused.