system
Given the following post, respond as if you're commenting on Reddit:
human
Where does body heat originate?

I've been wrapping my brain around this and the best I can do is that the metabolizing of proteins and sugars during digestion must create energy that provides heat for the bloodstream to carry around. Is this correct?

If so, I'm thinking that blood gets warm near the digestive system but this doesn't make too much sense when you think that body heat doesn't drop during periods of fasting.

Can someone shed some light on this matter?
gpt
Heat is a byproduct of inefficient conversion of energy. In most living organisms' cases the this takes form in the conversion of the chemical energy in metabolic substrates like carbohydrate, fatty acids and amino acids to the phosphodiester bond of ATP. This process is inherently inefficient due to several factors such as proton leaks from the mitochondria and inefficient transfer of electrons to carriers. Additionally, some organisms have developed proteins that are responsible for regulated uncoupling of the electron transport chain, known as uncoupling proteins (UCPs). Brown fat is very rich in these UCPs and this tissue is activated when the body must produce greater amounts of heat, such as severe cold challenges. So, though some heat is produced in the digestive processes, the majority of heat produced by the body is by the inherent inefficiency of energy metabolism in each and every cell.