If a person were fasting and hadn’t eaten for several days in a row, which source of energy would the body use as a last resort?

Protein is the last energy source of the body. The way with which the body uses energy is to burn carbohydrates first as an immediate supply; then fats are burned to accommodate the demand for more energy in prolonged activities; while protein is the last resort of energy of the body. Proteins can only be used up by the body when there are no more calories to be burned and the energy stores have also been depleted. Food deprivation and starvation could cause the body to use up protein as its final survival method.  

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