Our food consists chemically of carbohydrates, proteins, fats, vitamins, minerals and water. The fats are present in the food as such or in a combined form.
Fats, that we take, are derived from animal source(ghee and butter) or from vegetable source (different vegetable oils and hydrogenated vegetable oil)
Combined with carbohydrates and proteins, fat is present in milk, meat, eggs, lentils, cereals, nuts etc.
Fats are digested in the stomach and the intestines and absorbed from there into blood circulation. Some of them are used up to supply caloric needs of the body for performing various functions. The surplus ones are stored as such in different parts of the body.
Fats are made up of different fatty acids and glycerol. In some fatty acids, all the carbon (C) atoms are completely sandwiched between hydrogen (H) atoms.
It means that in them all C atoms are fully attached with or saturated with H atoms. Such fatty acids are called saturated fatty acids and when they combine with glycerol, they form solid saturated fat.
When in a fatty acid, some of the carbon atoms do not have hydrogen atoms attached to them, that fatty acid is called unsaturated. Its combination with glycerol gives rise to liquid unsaturated fats.
The larger the number of unattached carbon atoms (polyunsaturated), the more liquid and unsaturated the fat.
Animal fats such as butter and ghee contain predominantly saturated fatty acids and hence they are solid at ordinary temperature.
On the other hand, vegetable fats contain predominantly unsaturated fatty acids and hence they are liquid at ordinary temperature. Most fats contain both saturated and unsaturated fats in varying proportions.
In order to solidify certain vegetable oils, they are subjected to hydrogenation of their carbon atoms.
In the process, the oils are treated with hydrogen gas at a suitable temperature in the presence of a catalyser such as finely divided nickel.
Fats in the Blood:
After absorption, the fats in the blood stream move about either as tiny particles of fat, or they combine with different proteins so that in this form they are soluble in the blood stream.
The particles of neutral fat in the blood chemically called triglycerides, are very tiny, about one micron in size that is why they are called chylomicrons (chyle is the white milky product formed as a result of digestion of fats in the food).
A chylomicron is about one-seventh the size of a red blood cell.
In combination with different proteins, the fats form even smaller globules than the size of chylomicrons. They are called lipoproteins and according to their characteristics, they are categorized as:
Very Low-density Lipoproteins (VLDL);
Low-density Lipoproteins (LDL), previously called as beta-lipoproteins;
High-density Lipoproteins (HDL), previously called as alpha-lipoproteins.
The globules of these lipoproteins are made up of a core which is a mixture of fats and cholesterol. Covering the core is a layer of phospholipids, i.e. a kind of fat which contains in addition phosphoric acid and protein groups.
Serving as a coating for the entire globule is an extremely thin layer of proteins. In these globules, fat dissolves the cholesterol which otherwise cannot be transported by itself as it is insoluble in the blood as such.
And as pure fatty globules stick together, a layer of phospholipids and proteins removes this tendency.
If the fats and cholesterol are to be carried by the blood to their destinations in the tissues, these four substances, viz., fats, cholesterol, phospholipids and proteins must always remain linked together.
The thicker the protective coat of phospholipids, the more stable the globule. The smallest of the lipoprotein globules, HDL, has the heaviest coat and hence is the most stable.
It has been lately discovered that HDL have an inverse relationship to LDL. Epidemiologic and experimental studies have shown that high levels of HDL lessen the incidence of atherosclerosis.