Question

Why pure proteins and fats are never used as respiratory substrates?

Answer 1

Though pure fats or proteins cannot be directly used as substrates, they can enter as intermediary substrates of glycolysis and the Krebs’ Cycle. Proteins and fats have to undergo a series of chemical reactions to form simple compound and then only they can enter Krebs Cycle. After forming simple compounds only then they can enter the cycle and help to produce energy which takes a lot of time. Due to these reasons pure proteins and fats are not used as respiratory substrates.