Foods in general contain two types of fat namely 'visible fats' and 'invisible' or 'hidden' fats.
Visible fats are fats extracted from the following sources. a. Oil seeds : coconut, corn, cornseed, groundnut, mustard,
palm, rice bran, safflower, seasame, soyabean, sunflower and hydrogenated vegetable oils (vanaspathi).
b.Animal fats: Butter and Ghee.
c. Fish oils:Shark and cod liver oils.
Invisible or hidden fats:
Invisible or hidden fats are those which form an integral part of foods and are therefore not visible. It includes the fats present in the cells and cell walls and cell membranes of both plant and animal tissues.
Almost everything we eat as listed below carries some invisible fats.
a) Plant food - Cereals, millets, vegetables, spices, nuts and oil seeds, coconut, avacado.
b) Animal food - Milk and milk products (curd, cream, cheese), flesh foods, (mutton, beef, pork, chicken) organ meats (brain, liver, kidney), fish, shrimp, prawn.
Sources of Saturated Fat:
Saturated fat is resistant to oxidation even at frying temperatures. Examples are
a) Plants - coconut oil. Hydrogenated vegetable oils. Palm kernel oil.
b) Animals - Butter, ghee, fats from flesh foods and organ
Sources of Unsaturated Fat:
Unsaturated fats and oils include mono unsaturated fatty acids and PUFA in various proportions.
Important sources of unsaturated fats are as follows: Plant sources:
All common vegetable oils with the exception of coconut oils are predominantly unsaturated. The invisible fats present in nuts and oilseeds, cereals, pulses and legumes, roots and tubers, vegetables, spices and fruits.
In most plant foods and vegetable oils linoleic acid is the predominant PUFA, but mustard and soyabean oils, legumes/pulses. Fenugreek leaves, and green leafy vegetables are good sources of alpha linolenic acid.
The muscles (lean meat) of flesh foods, unlike the depot fat surrounding the tissues is mainly composed of cholesterol esters and phospholipids, both of which have a high proportion of long chain n-6 PUFA which are otherwise formed in the body from linolenic acid.
Arachidonic acid is found in animal and human cells. Fish and fish oils provide long chain n - 3 PUFA.
Hydrogenation (addition of hydrogen at double bonds) converts liquid oils into semisolid or solid fats. During hydrogenation, linoleic and alpha linolenic acid present in the oils are converted to trans fatty acids and saturated fatty acids. Also, the monounsaturated fatty acids are converted to saturated fatty acids.
Hydrogenated fats were designed to imitate ghee. It is used to prepare processed foods like biscuits and cakes. Vanaspathi is produced in India by hydrogenation of vegetables oils.
Cholesterol is a constituent of animal foods but is absent in plants. Vegetable oils do not have cholesterol. In human diets, cholesterol is obtained from ghee, butter, cheese, milk, curd, egg, flesh foods, organ meats, fish and prawns. Most animal foods are good sources of both cholesterol and fatty acids.