Why does fat produce more calories than carbohydrates?

Fat produces more calories than carbohydrates primarily because fat molecules contain a higher proportion of carbon and hydrogen atoms in relation to oxygen. This molecular composition allows for more energy to be released during the metabolic process of oxidation. When fat is metabolized, it goes through a process that breaks it down to release usable energy; due to its structure, fat can yield more ATP (the energy currency of the cell) compared to carbohydrates.

Fat, being a more energy-dense macronutrient, has more bonds that can be broken during metabolism, which contributes to its higher caloric value—about 9 calories per gram compared to carbohydrates, which provide approximately 4 calories per gram. This is crucial in understanding why dietary fats are an important energy source, especially in contexts where energy density matters, such as in weight management and athletic performance.

The molecular size of fat, while larger than carbohydrates, is not the primary reason for the difference in caloric content. Rather, it is the chemical composition that is fundamentally responsible for the difference in energy yield.