Exercising after eating...

How ever long it takes so you don't barf.

Depends on what you eat. If you eat a heavier meal, you're more likely to feel crappy and sluggish while working out, so you may want to wait longer or eat lighter. If I'm going to be working out within 45 minutes, I'll eat a mini-meal with mostly carbs and a little protein/fiber in it. That way I have fuel to work out and a little protein/fiber to sustain. I work out in the morning, so my typical breakfast the past week has been a half PBJ on wheat and a piece of fruit like a orange or a banana.

It's all about how you feel, but also depends on the type of training you're doing, whether it be HIIT or sustained cardio. You definitely want to eat an hr before HIIT, whereas eating before sustained lower-impact cardio isn't as important.

I agree with what most everyone else is saying. I have a hard time eating then working out, because I either feel like I'm going to throw up or I actually do throw up. So just wait for the right amount of time for your body, where you think you can workout and feel good doing it! Good luck!

Mama always said to wait 30 minutes after eating before getting in the pool.

now this is 100% true

I have to wait at least 2-3 hours between eating and working out - or I'll throw up. I know other people who can eat, go right to the gym, workout for an hour and be fine. Do whatever works for you.

Super variable. I can eat heavy and go right to exercise without an issue. Experiment and see how you feel.

I can (and have done) eat steak/eggs/homefries and go in to do vigorous exercise half an hour later and be fine. My friend who was with me ate half a chicken wrap and still felt ill-ish for the first half-hour of exercise.

As a matter of fact, having fat/protein shortly before exercise helps keep my energy level up.

Why should you eat before HIIT?
Did my regular 20 mins today on an 18 hour fast, felt great!

Because HIIT is total carb burning, except for the recovery. You can easily burn through the liver's remaining stores, just as you did, after an 18 hr fast. Shoot, after your overnight fast during sleep.

So the only way for your body to keep the blood sugar high enough was to break down muscle to convert to glucose. Glucose stores in the muscle can NOT be put into the blood stream, so if (and that is iffy depending on what your workout was yesterday and how many carbs you ate) there was extra glucose stores, the only muscle breakdown was for blood sugar - feeding the brain. If your muscle glucose stores are depleted because you worked out yesterday too, then more muscle breakdown for energy needs.

Yes, you burned muscle.