Why does Leon only drink milk in the movie ‘Leon’?

Why does Leon only drink milk in the movie ‘Leon’?

I recently watched this film and was wondering what the score was with the milk drinking.

I have read that it is to show he is innocent as much as he is a professional killer and it is a ‘child like’ quality.

I think maybe it is because he is always in training (sit-ups, muscle building etc), therefore milk is an easy way to stay on top form for the job he is doing.

What do you think?