Which macronutrient provides the body with the most energy per gram?

Which macronutrient provides the body with the most energy per gram?

• A. Carbohydrates
• B. Vitamins
• C. Fats
• D. Proteins

Answer: (C)

Energy density of macronutrients is the key idea here. Fats provide the most energy per gram because, when they are metabolized, they yield about 9 kilocalories per gram. In comparison, carbohydrates and proteins both supply roughly 4 kilocalories per gram. Vitamins, on the other hand, are micronutrients and do not supply energy. Their role is to support metabolism rather than provide fuel. The high energy yield of fats comes from their chemical structure being highly reduced, which allows more ATP to be produced during oxidation. That makes fats the body's most energy-dense fuel and the main long-term energy store, while carbohydrates serve as quick, readily available energy and proteins are primarily for tissue maintenance and, when needed, can contribute a smaller amount of energy.

Energy density of macronutrients is the key idea here. Fats provide the most energy per gram because, when they are metabolized, they yield about 9 kilocalories per gram. In comparison, carbohydrates and proteins both supply roughly 4 kilocalories per gram. Vitamins, on the other hand, are micronutrients and do not supply energy. Their role is to support metabolism rather than provide fuel. The high energy yield of fats comes from their chemical structure being highly reduced, which allows more ATP to be produced during oxidation. That makes fats the body's most energy-dense fuel and the main long-term energy store, while carbohydrates serve as quick, readily available energy and proteins are primarily for tissue maintenance and, when needed, can contribute a smaller amount of energy.