Q How much fat is essential in human diet?
A One gm per day.
(About one third of a teaspoon)
Q You mean man can practically do without fat in the diet!
A Yes. Apart from the 1 gm of fat containing essential fatty acids. Each cell of our body needs fat in its outer membrane and a tiny bit inside some cells. Many organs, particularly the brain, have large amounts of fat. We also need “storage fat” for bad times. But we have an excellent biochemical machinery which can convert ingested carbohydrate and proteins (these, of course, are essential) in the diet into any type of fat the body requires.
Q If fats are so inessential, why do human beings crave for them?
A There are three reasons:
(i) Fats make food tasty.
(ii)Fats are concentrated sources of energy.
Each gm of fat produces 9 calories of energy while 1 gm of carbohydrate produces only 4.5 calories. For living beings with high caloric needs fats are an economical way of eating. Meat-eating animals, which incidentally also eat a lot of fat, like the lion, needs to eat only once in three or four days.
Vegetarian animals, like rabbits or monkey, get little fat in their diet. They have to eat every hour of their waking lives.
(iii) Fats give a sense of fullness. After a fatty meal, one can think of things other than food.
Q What are these essential fatty acids and why are they essential?
A To understand this a little biochemistry is unavoidable. A fat is a triglyceride. One glycerol molecule is attached to three fatty acids. Fatty acids have the following general formula —
A lot of -CH2 between — COOH and CH3. The glycerol attaches to the -COOH (carboxyl) end, one glycerol to three fatty acids to make triglyceride which is fat.
The carbon atoms in the chain are attached to each other by single bonds most of the time. If each C atom of a fatty acid is attached to the other by a single bond (and to 2 Hatoms in addition), that fatty acid is said to be saturated (i.e saturated with hydrogen).
At times, however, there are double bonds between some adjacent C atoms (in which case each C atom of the pair is attached to only one-H atom). Fatty acids with one or more double bonds are called unsaturated fatty acids. If there is only one double bond in a fatty acid, it is called mono-unsaturated; if there is more than one double bond it is called polyunsaturated.
The biological activity of a fatty acid depends on:
(1) The length of the CH2 chain(short chain, medium chain, long chain fatty acids).
(2) The presence and the number of double bonds (monounsaturated or polyunsaturated).
(3) The position of the first double bond in the unsaturated fatty acids. The C atoms are numbered from the methyl end and the first atom of C is termed omega, 1, the second omega 2 and so on towards the — COOH end.