Why are proteins rarely used as an energy source?

Amino acid protein monomers are a valuable raw material for the construction of new protein molecules. Therefore, complete cleavage of polypeptides to inorganic substances is rare. Consequently, the energy function, which consists in the release of energy during complete breakdown, is performed quite rarely by proteins.
This is disadvantageous, it is more advantageous to use lipids. Proteins also perform many important functions in the body.

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