Fat is a reserve form of fuel

The lipids in foods and in the human body, though many in number and diverse in function, generally fall I three classes: triglycerides, phospholipids, sterols.

When the people speak off at, they are usually talking about triglycerides. Most animal fats are saturated and hence, solidify at low temperatures.

Most vegetables oils are unsaturated and, hence remain fluid.

Oxidative breakdown of fats yields more than double the amount of energy yielded by glucose, because of their poor oxygen contents.

These can be stored in an almost pure unhydrated form in large amounts in lesser space. Fat is stored with a very minimal amount of water, so fat stores are more compact and thus store significantly great amounts of energy than carbohydrate reserves.

Hence, fats serve as the best storage of spare energy in the form of ‘reserve stored food’. Gram for gram, fats provide more than twice the energy of carbohydrate or protein, making fat the most efficient storage form of energy.

The body fat found on a normal-weight person contains more than enough energy to fuel an entire marathon run or to battle disease should the person become ill and stop eating for a while.

For the typical 125 pound woman, roughly 20 percent of body weight – about twenty five pounds – is fat. 

Statistically, most of people carry more than that. Excessive fuel storage over the long haul taxes the body, precipitates disease and shortens life.
Fat is a reserve form of fuel