Tasks of fat in the body
Adding 1g of fat to the body is the equivalent to 9 kcal of energy. It is thus the most energy-dense nutrient, as proteins and carbohydrates bring only 4.1 kcal per gram. In addition, carbohydrates and proteins are often in food bound to a lot of water and thus have a different volume. As an example, rice rises to 3 times its original volume during cooking, because carbohydrates can bind easily to water. Fat, on the other hand, cannot do a bond with water (hydrophobic or lipophilic) and is therefore in a more concentrated state in food.
Fat is the most important energy storage for the human organism. Although short-term carbohydrate energy production is more effective, the body can only store carbohydrates as glycogen to a limited extent in the liver and muscles. The average person has about 400g of carbohydrates stored and even for a competitive athlete, the glycogen stores often do not exceed more than 600g of carbs.
Fat, however, can be stored by the body indefinitely (given no energy deficit). You can see the fat depot places: in the first place, the obviously visible ones like love handles, bellyfat, thick thighs, etc. The remaining subcutaneous fatty tissue is distributed over the entire body, but not always evenly. Wwomen are more likely to store their fat on the buttocks, hips and arms, while men are more likely to have fat around their abdomen. But fat can also be stored in muscles and organs (organ capsule, fatty liver, connective tissue). An average man is made up of 15-20% body fat, while a woman has about 25% body fat. It is important to note that 1g of human fat tissue, in contrast to dietary fat, has only 7 kcal (instead of 9 kcal). For comparison, the body fat percentage of a competitive bodybuilder on stage can range between 3-5% body fat.
In addition to its function as an energy depot, fat also has other functions for the body, e.g. fat under the eyes to hold the eye in place. Fat deposits under the skin are also effective cold protection, as well as a protective pad from injury. As such, fatty coats surround the major organs (organ capsule and are for protection from cold and mechanical injury.
As a third important function, fat serves as a source of fat-soluble essential nutrients, such as polyunsaturated fatty acids or lipophilic vitamins of groups E, D, K and A. If dietary, essential fat is not available or provided for a long time, it can lead to deficiency symptoms. This also makes it clear why a too low-fat diet is not healthy for the body in the long term (there are also a lot of other reasons of course, like a dysbalance in hormones).
Of course, fats or fatty acids have more functions in the body. They are involved in the production of endogenous hormones (e.g. cholesterol for testosterone production), help in the transport of fat in the blood (HDL, LDL) or play a special role as a part of the membrane in every cell (lipid bilayer).
Furthermore, the body can also produce prostaglandins from them. Prostaglandins are messenger substances in our body that can determine blood pressure, blood coagulation, the salt and water balance, and inflammatory agents. We need prostaglandins that promote inflammation so we can fight infection. But we also need prostaglandins, which can slow down inflammation again. Both must be in a reasonable balance.