In food, why do fats produce more energy than carbohydrates?

Question

In food, why do fats produce more energy than carbohydrates?

Answer 1

during the process of combustion, of food in our body(in order to release energy),

carbohydrates have enough oxygen contained  in them which is required for the process.

fats do not have enough oxygen so they take oxygen from outside the body...as a result of which they take more than enough amount of oxygen and hence  

release about a double amount of energy. This is because larger amount of oxygen carries out good combustion

Answer 2

They contain more hydrogen that isn't already oxidized, so the oxidation of that hydrogen is available to release energy.  Glycerol, the basic fat, is C3O3H8, which leaves the 3 carbon and 2 hydrogen atoms available for oxidation.  The basic carbohydrate is the monosaccharide, which is (CH²O)n, leaving only the carbon atom available for oxidation.

Answer 3

Sources that you may use:

http://en.wikipedia.org/wiki/Fat

Answer 4

Fat is simply a concentrated form of carbohydrates that organisms make. Hence, more energy by density.