Edited by Dr. Davide Marciano
Structure and Functions of Lipids
For a very long time, and still today, lipid supply has been thought to be synonymous with body fat. Even more serious is the alleged role of fat in promoting cardiovascular disease and cancer.
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It is undeniable that some types of fats play a fundamental role in the functioning of our organism.
Although they have an energetic function, they are essential for many bodily functions, in fact they are the precursors of some hormones, they are a structural part of cell membranes, they provide LIPOSOLUBLE VITAMINS (soluble in fats) A, D, E, K etc. (for further information: the functions of lipids).
The characteristics of a fat are determined by the presence or absence of double bonds between two or more carbon atoms. In fact we have:
- SATURATED FATTY ACIDS, free from double bonds
- UNSATURATED FATTY ACIDS, have double bonds and based on their number are divided into:
a) Monounsaturated, with only one double carbon bond
b) Polyunsaturated, with more double carbon bonds.
Lipids and health
The physical properties of saturated and unsaturated fatty acids are different.
Lipids containing saturated fatty acids are all solid at room temperature, while lipids containing unsaturated fatty acids are all liquid.
This explains why lipids of animal origin are solid (fats) and those of plant origin are liquid (oils).
Saturated fats must be consumed very sparingly because they are considered as harmful, while unsaturated fats must represent a good percentage of the daily caloric quota (20 - 30%). Monounsaturated are the best choice ever (a typical example is olive oil rich in omega-9).
Since in man some polyunsaturated fatty acids are essential for correct metabolism (linoleic, arachidonic, linolenic acid) it is necessary to introduce these substances, called ESSENTIAL FATTY ACIDS (AGE), in the daily diet.
Among the polyunsaturated fats we mention: OMEGA-3 FATS or FISH OILS.
Fat provides 9 Calories per gram.
Digestion and absorption of lipids
To be digested, lipids require a maximum of time and effort, because they are insoluble in water and have a complex structure.
Their digestion begins in the stomach with an enzyme called GASTRIC LIPASE, however its action is limited by the high acidity of the stomach.
The complete digestion of fats takes place in the small intestine, in a part called DUODENUM. Here they interact with the secreted bile of the gallbladder and are transformed into smaller particles. The reduction of fat particles allows the enzymes that break them down (LIPASE) to break them down into progressively smaller particles.
Therefore the original form of triglycerides is first converted into diglycerides, then into monoglycerides and finally into fatty acids and glycerol.
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