Final answer:
Under starvation conditions, fats serve as the primary fuel supply for the body. Initially, the body uses stored carbohydrates, but as starvation persists, it turns to fats as the main energy source. Proteins are important for tissue maintenance but are not the primary energy source in this scenario.
Step-by-step explanation:
Even under conditions of starvation, the nutrient that serves as the primary fuel supply is fats(b). Fats are one of the major macronutrients, along with carbohydrates and proteins, which are essential to human survival. Initially, during periods of starvation, the body relies on stored carbohydrates; however, these stores are quickly utilized. As starvation continues, the body turns to fat reserves to provide energy. This energy comes from the breakdown of fats into fatty acids and glycerol, which can then be further metabolized to generate ATP, the energy currency of the cell.
Proteins are also a critical nutrient, primarily serving as building blocks for body tissues rather than primary energy sources. Consuming proteins helps to maintain muscle mass and other vital functions.