During the oxidation of 1 g of proteins, the same amount of energy is released as during the oxidation of 1 g of carbohydrates

During the oxidation of 1 g of proteins, the same amount of energy is released as during the oxidation of 1 g of carbohydrates. Why does the body use proteins as an energy source only in extreme cases?

The functions of proteins are, firstly, building, enzymatic, transport functions, and only in extreme cases the body uses or spends proteins to get energy, only when carbohydrates and fats do not enter the body, when the body is starving.

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