I would just run along the south bank of River Main until Obermainbrücke and then cross tbh. There's major construction on the original route, and the security situation in Kaiserstrasse (after Hauptbahnhof) has gotten worse over the last couple years.

Mamma Forno near Konstablerwache S-bahn is friendly, inexpensive, with good simple food, and will not judge men in running clothes.