You'll be fine! There, do you feel better now?!

I've always been interested in the effect of heavy exercise for a week followed by carbo cramming the last 36 hours before a test. In theory the body should shed fat during exercise releasing toxins that show up in a test. When you carbo cram the body would then switch to storing fat again so it would not be releasing the toxins that show up in a test, right? Is this just a bad pseudo-science based on 30 year old 10th grade biology? Curious if anyone knows the answer.