Not OP but when I was running 60+ miles a week, I wouldn’t eat before most runs but I would get up about 2 hours before starting my long run on Sundays to eat a bagel or bowl of oatmeal or something similar. 15-20 miles was just too far for me to go on an empty stomach even if I used a gel or two during the run.

I did always try to get a morning bowel movement before starting my runs though.