Tuesday, 10 April 2018

Fats - intro

The fats, also known by the scientific (fancy) name of lipids, are digested and released in the blood stream, as lipoproteins (ULDL, HDL, LDL), and then stored as fat tissue. An important role is played by the essential fatty acids (linoleic acid and linolenic acid), but about this we will write a bit later.

There are different tipes of fat, and the first classification is by saturation grade (saturated (triglycerides, phospholipids, sterols) and unsaturated. Out of dietary lipids, the triglycerides make 95% of our daily fat. A triglyceride is made from 3 fatty acids linked via a glycerol molecule.
Another classification is made according to the state of the lipids at room temperature - if solid  is called fat, if liquid is called oil.

Fatty acids - are made from a chain of hydrogenated carbon atoms connected to a carboxil group. The chain length could be anywhere between 3 to 24 carbon atoms. The degree of saturation is related to the number of double bonds - unsaturated fatty acids got at least on double bond (mono-unsaturated f.a. has one, poli-unsaturated f.a. at least two double bonds). Point of unsaturation - where the double bonds are located in the fatty acid molecule - n (omega) and delta designation (shows all double bonds. The most abundant fatty acids in our food are oleic and palmitic acids (2/3 of our daily intake).

According to the point of unsaturation, the most common acids in our diet are C16:0 - palmitic acid, C18:0 stearic acid, C18:2 linoleic acid, C18:3 linolenic acic and C18:1 oleic acid.
The lenght of the chain is related to the melting point, shorther the chain, lower the melting point. The more unsaturated, the lower the melting point also. Liquids such as vegetable oils (made from sunflower, corn, olive, peanut, canola or soy) are mostly unsaturated, while solid fats like butter are mostly saturated fatty acids.

Triglycerides are mostly saturated, more stable and less prone to oxidation (one of the important oxidation reaction is the hydrogenation - unsaturated fatty acids become saturated). Hydrogenation is a common process in food manufacturing (or used to be) but it is also transforming the Cis fatty acids in Trans fatty acids, with negative influence on health. The Trans fatty acids are made during industrial processing and in the stomach of ruminants such as cows.

Phospholipids contains a diglyceride, a phosphate and a simple organic molecule such as choline. The got a polar and an apolar side (amphipathic properties). Are major components of cell membranes (you can find them in plant and animal food). They are added during food preparation as emulsifiers, to help the oil and the water to create a stable emulsion (prevents oil and water to separate). They line up tail-to-tail in the membrane of the cell to form a bylayer, as a barrier for entry of many molecules into the cell.

Sterols are the third lipid component in the diet. The main one is known as cholesterol, found in foods of animal origin. The plants have sterols and stanols, most of them being eliminated via stools. Added to the food to reduce the absorption of cholesterol, they can potentially lead to a 10% reduction of the cholesterol in the blood stream .

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