Why do fats provide more energy per gram than carbohydrates and proteins?

Fats, which are primarily composed of triglycerides, provide more than twice the energy per gram compared to carbohydrates or proteins.12

This difference exists because fats and carbohydrates are metabolized differently by the body. While carbohydrates like glucose and glycogen are essential energy sources, they are more oxidized than the fatty acids found in lipids. The oxidative metabolism of triglycerides yields significantly more energy because their chemical structure is more reduced, meaning they contain a higher proportion of carbon-hydrogen bonds that can be oxidized to release energy.1

In contrast, carbohydrates and proteins contain more oxygen within their molecular structures, which results in a lower energy density per unit of weight. Consequently, fats serve as a highly efficient form of energy storage in adipose tissue, allowing higher animals to store large amounts of energy in a relatively compact form.12