MCQ Detailed View

The human body produces energy by metabolizing macronutrients such as carbohydrates, proteins, and fats. Fats are the most energy-dense macronutrient, providing more calories per gram than carbohydrates or proteins.

The heat energy released during metabolism is known as the calorific value. For fats, the average calorific value is about 39 kJ per gram (9 kcal/g). This energy is used by the body to perform physiological functions such as maintaining body temperature, muscle contraction, nerve transmission, and other cellular processes.

Fats are chemically composed of long chains of fatty acids esterified to glycerol. During metabolism, fats undergo oxidation reactions in the presence of oxygen to produce carbon dioxide, water, and energy. The general reaction for fat metabolism can be represented as:

$$\text{C₁₆H₃₂O₂ + 23 O₂ → 16 CO₂ + 16 H₂O + Energy}$$

Here, the energy released is largely in the form of heat, which the body can use for mechanical work and maintaining homeostasis. Compared to carbohydrates, which release approximately 17 kJ per gram, and proteins, which release approximately 17 kJ per gram, fats provide more than twice the energy.

This high energy yield is the reason fats serve as the primary energy storage in the body. Energy from metabolizing fats is measured using calorimetry, and it is important in nutrition science, physiology, and diet planning.

Therefore, the heat energy produced when the human body metabolizes 1 gram of fat is 39 kJ, making fat the most energy-rich nutrient for sustained energy supply.