Fat is one of the main marcronutrient. The other two being protein and carbohydrate. Fat is also commonly known as triglycerides which are essentially esters of three fatty acid chains and the alcohol glycerol.
The term "fats" and "oils" are often confused by many people. To simplify:
Fats - generally solid at room temperature and high in saturated fatty acids.
Oils - generally liquid at room temperature and low in saturated fatty acids
"Lipid" on the othe hand is a general term. Lipids are not necessarily a triglyceride.
Fat serves as a major function of supplying energy. Besides that, stored fat is also important as a thermal insulator, and in some warm-blooded animals, as a source of heat for maintaining body temperature.
There are several types of fats, but each variation is essentially on the same chemical structure. All fats are derivatives of fatty acids and glycerol. Generally, fats are glycerides, particularly triglyceride, which are molecules made from the combination of one molecule of glycerol with three fatty acids (Figure 1).
Figure 1: Triglyceride structure
In Figure 1, one chain of fatty acids is bonded to each of the -OH groups of the glycerol by the reaction of the carboxyl end of the fatty acid (-COOH) with the alcohol. Water (H2O) is then eliminated and the carbons (C) are linked by -O- bond through dehydration synthesis. This process is known as esterification and hence, fats are essentially esters.
Saturated Fats: Fats that contain no double bonds in their fatty acid chains. These fats tend to be solid at room temperature.
Unsaturated Fats: Fats that contain some number of double bonds in their structure. They are generally liquid at room temperature. Unsaturated fats can be either polysaturated (many double bonds) or monosaturated (one or few double bonds).
Table 1: Common fatty acids of natural fats and oils
Fatty acid chain often differ by length and are categorized from short to long:
Short-chain fatty acids (SCFA) are fatty acids with aliphatic tails of fewer than six carbons.
Medium-chain fatty acids (MCFA) are fatty acids with aliphatic tails of 6–12 carbons.
Long-chain fatty acids (LCFA) are fatty acids with aliphatic tails 13 to 21 carbons.
Very long chain fatty acids (VLCFA) are fatty acids with aliphatic tails longer than 22 carbons.
Most fats found in food, whether vegetable or animal, are made up of medium to long-chain fatty acids, usually of equal or nearly equal length.
Other Importance Of Fat
Besides providing energy, fats are also sources of essential fatty acids, which is an important dietary requirement. Vitamins A, D, E and K are fat soluble, which means that they can only be digested, absorbed and transported in conjunction with fats
Fat also serves as a useful buffer against a host of diseases. When a particular substance, whether chemical or biotic, reaches unsafe levels in the bloodstream, the body can effectively dilute—or at least maintain equilibrium of—the offending substances by storing it in new fat tissue. This helps to protect vital organs, until such time as the offending substances can be metabolized or removed from the body by such means as excretion, urination, accidental or intentional bloodletting,sebum excretion, and hair growth.