system
Given the following post, respond as if you're commenting on Reddit:
human
What do you catabolize first during starvation: muscle, fat, or both in equal measure?

I'm actually a Nutrition Science graduate, so I understand the process, but we never actually covered what the latest science says about which gets catabolized first.  I was wondering this while watching _Naked and Afraid_, where the contestants frequently starve for 21 days.  It's my hunch that the body breaks down both in equal measure, but I'm not sure.

EDIT: Apologies for the wording of the question (of course you use the serum glucose and stored glycogen _first_).  What I was really getting at is at what rate muscle/fat loss happens in extended starvation.  Happy to see that the answers seem to be addressing that.  Thanks for reading between the lines.
gpt
Gluconeogenesis highly prioritizes fat metabolism for energy when carbohydrate based sources of glucose are low/empty. The entire purpose of fat is to be an energy source when other sources are low, whereas the purpose of muscles are either locomotion or stability. It would be hard to imagine evolution leaving you as an atrophied blob of fat in an emergency situation.