Question

A pound of butter contains more usable energy than a pound of sugar for a human because

Answer 1

Butter is a source of fat and sugar is a source of carbohydrate.  

Fats are the slowest energy source, however, they are the most energy-effective source of food. Each gram of fat supplements the body with about 9 calories of energy, which is more than two times than that of the energy obtained by carbohydrates or proteins.  

As the fats are such an effective energy form, the body accumulates any excess energy in the form of fats.  

Answer 2

A pound of butter contains more usable energy than a pound of sugar for a human because when fat is consumed in the form of butter then it can be broken down by body fluids easily.

However, if sugar is consumed more, then it becomes difficult to get broken down.