Health: Why fried preparations are good for deities, but not so good for us
To eat preparations fried on refined vegetable oil is not a very wise idea. One reason is that we end up eating a lot of refined vegetable oil, which will produce inflammation and other problems. On top of that, there are the toxic compounds produced when the oil is heated to high temperatures.
Different from ghee and coconut oil, refined vegetable oils are rich in polyunsaturated fatty acids. Research shows that these unstable fats produce aldehydes (chemicals that are highly cancerogenous) as well as trans-fats and other dangerous compounds when heated to high temperatures (Health effects of oxidized heated oils, Foodservice Research International 13(1):41 - 55 · June 2006). A simple portion of french fries prepared on refined vegetable oil can contain up to 100 times the safe daily limit of aldehydes set by the World Health Organisation.
Fried preparations made in pure ghee are much better: not only is ghee actually good for the body, but it's very satiating, due to the high concentration of saturated fat. This makes ghee a kind of self-limiting food, since one will naturally feel full and stop eating. It's more difficult to overeat.
Although foods fried in ghee are better, there are still reasons to be careful. First problem is that most of the time, we fry something made out of white flour (imagine a puri, pakoras or an alu-patra). Or the white flour is the main ingredient, or it's close to it. To make matters worse, we frequently also add sugar. It’s exactly this combination of refined carbohydrates and fat that makes these preparations so palatable. The main problem with this combination is that it's very fattening. And we are not just talking about the calories, but the way the body metabolizes the fat when it's consumed in combination with refined carbohydrates.
Normally, when we eat fat, the body burns it for energy. There is a limit on how much fat the body can process at a time, therefore one feels full quickly, and thus stops eating. Ironically, eating fat does not usually make one fat. However, when fat is ingested in combination with refined carbohydrates, the spike in insulin caused by the carbs makes the body store the fat (as well as most of the carbohydrates), instead of burning it. Although fat reduces the glycemic index of the food, still the presence of the refined carbs will trigger the release of insulin, leading to the accumulation of fat.
Another problem is that when starches are combined with fat and heated to high temperatures, they form stick molecules that are difficult for our body to absorb. It ends-up clogging the arteries, which is not good for the heart. Most people have the impression that saturated fat causes heart disease, but recent studies show that it is not exactly the fat, but the combination of fat and refined carbohydrates. One that eats too much refined carbs will end up overweight, with insulin resistance and eventually with type 2 diabetes. One that eats too much refined carbs in combination with a lot of saturated fat may be better in terms of insulin resistance and diabetes (since the fat blunts the insulin spikes caused by the carbs and sugar), but on the other hand he may end up obese and with heart problems, especially if he indulges in unhealthy fats.
Healthy fats in themselves are not bad. The problem is this combination of fat and refined carbs. You don't need to take fat away from your food. The answer is to combine it with vegetables and low-glycemic foods, instead of sugar and refined carbs (one can make a sabji with sauteed vegetables on ghee and some nuts, or make cookies using coconut oil, rolled oats and dates, for example). Naturally, another point is to avoid using refined vegetable oils.
Fried preparations should always be made in ghee and reserved to the deities and to festivals and other special occasions. It's ok to eat one or two samosas fried in ghee on festivals, the point is just to not make it a daily habit. If there is no money to buy ghee, it's much more intelligent to avoid the idea altogether and make some simpler, non-fried preparations.