Metabolic Energy Control

The metabolic energy control system of the human organism is designed to be fueled by either glucose (carbohydrates) or fatty acids (lipids).1, pp. 160  In a healthy individual, the fuel of choice is largely determined by diet composition and intake schedule.  Because food intake is a batch process for most people, the availability of food in the digestive system cycles daily through full, empty, full, and so forth.  Thus, for a diet in which the macronutrients (carbohydrates, proteins, and lipids) are consistent and in reasonable proportion, it is customary for the choice of fuel to switch back and forth seamlessly between glucose and fatty acids during the day in response to the alimentation cycles.
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