Question

Why are pure proteins and fats not used as substrate?

Answer 1

hyy..

⭐Both fats and proteins have to under undergo series of reactions to form simple compounds and  which are all converted into a  compound(acetyl coenzyme) that can enter Krebs’ cycle.  On the other hand glucose can act directly as a respiratory substrate as it is easy to oxidise and abundantly present in a body. 
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Answer 2

Both fats and proteins have to under undergo series of reactions to form simple compounds and which are all converted into a compound(acetyl coenzyme) that can enter Krebs’ cycle. On the other hand glucose can act directly as a respiratory substrate as it is easy to oxidise and abundantly present in a body.