On my rest days from weight training I do a 20-25 minute jog after breakfast how long should I wait before going on a run?
Well I don’t think you have to worry about losing muscle mass from just a short run without eating first. Not sure what you are basing this on. Eating before working out varies for everyone as mentioned earlier. I can run quicker than others after eating, depending on how much and what I eat. The worst that can happen is you have to slow down. Experiment and see what works for you.