Compare the energy yield from the oxidation of fats versus carbohydrates, and explain why fats are considered the body's most concentrated source of energy.

Fats yield about 9 kcal per gram, whereas carbohydrates yield about 4 kcal per gram. Fat catabolism produces roughly twice as much energy per gram as carbohydrate oxidation, and fats contain very little water, making them the body's most concentrated source of stored energy.

Comparing oxidation energy yields, fat catabolism provides about 9 kcal per gram, while carbohydrate catabolism provides about 4 kcal per gram. This means triglycerides release approximately twice as much energy per gram as either glucose or protein. The body also stores energy mostly as fat, since fat accounts for 80-85% of stored energy. Because fat contains very little water, it packs more energy into a smaller, lighter mass than carbohydrates, which are stored with more water and yield less energy per gram. In terms of oxidation chemistry, glycerol from fat can enter glycolysis after conversion to a glucose intermediate, while fatty acids are oxidized through beta oxidation in mitochondria, producing acetyl CoA that enters the citric acid cycle. These pathways are why fats are considered the body's most concentrated fuel source.