system
Given the following post, respond as if you're commenting on Reddit:
human
Where does excess protein go?

As per the title, is excess protein metabolized into fat (I didn't know we had the biological machinery for this process, but am not sure), is it removed via excretion, or does more of it go to muscle? Eating a pure protein diet does not mean all the protein consume goes into muscle, but is a higher proportion of it utilized in muscle than in a normal 1 g protein: 1 lb body weight diet?
gpt
Protein has stored energy that the body can use as calories just like it does with sugar or fat. If unused, the body can convert the energy to fat. The primary end products of amino acid digestion are ammonia, carbon dioxide, and water. Carbon dioxide is exhaled, while water and ammonia (converted to urea to prevent it from being toxic) are expelled through pee.

To be clear, if your body is trying to build new proteins (such as for muscle) it will use the available amino acids instead of metabolizing them further for calories. The body will only try to build muscle if you are using the muscles heavily and you are consuming sufficient calories. The body will not try to strengthen muscles that aren’t used much and it won’t grow any new muscle if it’s starving.