Fatty Acid Metabolism - Fatty Acids As An Energy Source

Fatty Acids As An Energy Source

Fatty acids, stored as triglycerides in an organism, are an important source of energy because they are both reduced and anhydrous. The energy yield from a gram of fatty acids is approximately 9 Kcal (37 kJ), compared to 4 Kcal/g (17 kJ/g) for carbohydrates. Since the hydrocarbon portion of fatty acids is hydrophobic, these molecules can be stored in a relatively anhydrous (water-free) environment. Carbohydrates, on the other hand, are more highly hydrated. For example, 1 g of glycogen can bind approximately 2 g of water, which translates to 1.33 Kcal/g (4 Kcal/3 g). This means that fatty acids can hold more than six times the amount of energy per unit of storage mass. Put another way, if the human body relied on carbohydrates to store energy, then a person would need to carry 67.5 lb (31 kg) of hydrated glycogen to have the energy equivalent to 10 lb (5 kg) of fat. Hibernating animals provide a good example for utilizing fat reserves as fuel. For example, bears hibernate for about 7 months, and, during this entire period, the energy is derived from degradation of fat stores.