The most common edible oils of India are: 1. coconuts, 2. sesame (til), 3. mustard, 4. ground-nut, and 5. linseed.
In this article I shall briefly discuss the food values of these oils in comparison with those of animal fats, as well as their comparative food values.
Animal Fats and Vegetable Oils
Both these classes of substances can be put under the common name fat. Fats are fuel foods, and in this respect vegetable oils are as good as animal fats; that is, weight for weight vegetable fats supply the same amount of energy as animal fats (e.g. ghee).
As for digestibility, the vegetable fats are well assimilated in the human system.
But animal fats are superior to vegetable fats in one important respect, that is, with regard to their vitamin contents. Vegetable oils contain very little or no fat soluble vitamin (A or D), whereas butter contains a fair quantity of those vitamins. Fish liver oils like halibut oil and cod-liver oil are very good sources of those vitamins. It must be mentioned here that ghee cannot be placed in the same category with butter. Ghee in this respect is inferior to butter and contains little or no vitamin depending on its method of preparation. The very inferior vitamin content of vegetable oils is more than counterbalanced by its cheapness. Very few people in India can afford to take butter. But no one need worry about it. There are cheaper sources of these vitamins.
In a sunny country like India vitamin D is easily available. Human skin contains ergosterol which on exposure to sunlight is converted into vitamin D. Vegetable oils on irradiation or exposure to sunlight also give rise to vitamin D as they contain ergosterol.* So rubbing the body with vegetable oils and subsequent exposure to sunlight is the cheapest and best way of getting vitamin D. It is an ancient custom in Bengal to rub the whole body of infants with mustard oil and then expose them to sunlight in the morning for some time, which is highly beneficial.
It is doubtful whether there is vitamin A at all in the vegetable world. But they contain carotene which is converted into vitamin A in the human as well as other animal systems. Raw carrots and spinach are excellent sources of carotene. Raw cabbage, yellow corn, peas and tomatoes are good sources. Sweet pumpkin, which is produced in large quantities in Bengal and which the poor villagers of Bengal take in fair amount, contains carotene. Other good sources are ripe mangoes and papayas. Poor people need not, therefore, rush to butter for vitamin A.
So considering the comparative prices of butter and ghee and vegetable oils I have no hesitation to say that for poor men vegetable oils are a fair substitute.
Comparative Food Values
The fat contents of cocoanut, sesame, ground-nut, mustard and linseed oils are practically the same. 98-99 per cent of them is fat. And all these fats supply the same amount of energy to the body. I have already said that all these oils are well assimilated in the human system, so the question of digestibility is not of much importance. Habit is a great factor in this. A Bengali would not like the smell of linseed oil at all. He would rather go without any oil than take linseed oil. Whereas those who are not accustomed to mustard oil would find it rather irritating to the stomach on account of its sulphur-containing substance. But when one can accustom himself to any of these oils there is no difficulty of digestion, and fat values of all of them are practically identical.
But there is one point to be considered, i.e., the non-fatty portion of these oils. They have not been thoroughly investigated from the nutritive point of view. Modern researches on vitamins have shown the importance of minute traces of substance in our diet. So it would be no surprise if one day scientists discover something in any one of those oils to declare its superiority over others. I am only hinting at the unknown possibilities which have up-till now not been brought to light. Minute traces of metallic compounds of manganese, nickel, cobalt and other rarer metals may have great biological values which are still unknown to us. Ash of the linseed oil contains .0006 per cent manganese.
In the present state of our knowledge we can only say that all these oils are more or less equally good and ore may take any one of them he finds cheap and suitable to his taste.
In conclusion I should like to say one word about the hydrogenated oils like cocogem, etc. They are known as vegetable ghee. These hydrogenated oils are inferior to the natural oils in point of digestibility. And whatever little vitamin they may contain is also lost during hydrogenation. I am, therefore, definitely of opinion that hydrogenated oils should never be taken specially as they are constlier than common vegetable oils. It would amount to buying inferior stuff at greater cost.