Go for an early morning run on an empty stomach. At this point you are in a fasted state as your last meal will have been 8-12 hours ago.

When in a fasted state your body's glucagon levels are at their highest and your insulin levels will be at your lowest.

Glucagon stimulates glycogenolysis, gluconeogenesis, lipolysis, protein degradation, amino acid catabolism and ketogenesis

You will lose muscle aswell as fat...probably pretty quickly.