Proteins are respired for energy primarily during which condition?

Proteins are respired for energy primarily during which condition?

• A. Never
• B. During starvation periods
• C. During growth phases only
• D. During digestion of fats

Answer: (B)

When the body has plenty of carbohydrates and fats, proteins are kept for their roles in growth, repair, and enzyme production rather than for energy. Energy from proteins is used only when those other fuel sources run low, as in starvation. During starvation, the body increases breakdown of body proteins to release amino acids, which can be converted into glucose (gluconeogenesis) and, after deamination, fed into the energy pathways to supply tissues. This shift means proteins become a significant energy source mainly during periods of starvation, making that condition the correct answer. The other scenarios don’t rely on protein breakdown for most energy—growth emphasizes synthesis of new proteins, and digestion of fats uses fatty acids for energy instead of relying on amino acids.

When the body has plenty of carbohydrates and fats, proteins are kept for their roles in growth, repair, and enzyme production rather than for energy. Energy from proteins is used only when those other fuel sources run low, as in starvation. During starvation, the body increases breakdown of body proteins to release amino acids, which can be converted into glucose (gluconeogenesis) and, after deamination, fed into the energy pathways to supply tissues. This shift means proteins become a significant energy source mainly during periods of starvation, making that condition the correct answer. The other scenarios don’t rely on protein breakdown for most energy—growth emphasizes synthesis of new proteins, and digestion of fats uses fatty acids for energy instead of relying on amino acids.