For some decades now, fat was regarded as the bad guy of nutrition and one of principal causes of heart diseases, high levels of cholesterol and obesity. This caused the low fat mania, with a variety of low or no fat food and diet plans that overwhelmed the market and pages of various health and beauty magazines. What happened is that most people who tried to control or loose their weight by means of low fat lifestyle failed.
There is more. Not all fat is bad. there are kinds of fat that are essential for proper functioning of the organism. Not knowing this and expelling all fat from one's diet as much as possible is detrimental to health.
Let us clarify something here
In the past, people ate much more fat than they do now. Almost half of all calories came from fat, and just over 10% of people were obese. Now a third of calories comes from fats, and every third person is obese. Are fats the cause for excess weight? Unlikely, what everybody seems to have forgotten is that calories come from other sources as well, such as simple sugars, which are overabundant in modern eating habits. Fat, which is hard to digest and makes us feel full for some time, has been largely expelled.
Widespread calorie bombs known as simple carbohydrates (such as sugar), go down in an instant and leave a gaping hole in our stomach after a short time. Also, our organisms depend on fat in most critical places. Cell membranes are built from fats and protein. Brain and nerves are mostly fat, it would be impossible to develop nervous system or keep it operating without fats. Heart is mostly fat-powered. Lungs, eyes, immune system, internal organs, all these require some form of fat to function properly, or at all.
The good and the bad
There are three kinds of fats, according to their chemical structure and resulting physical properties.
Monounsaturated and polyunsaturated fats are liquid at room temperature. They are typically found in plant oils, nuts and seeds.
Saturated fats are usually solid at room temperature. They mostly come from animal products such as meats, milk and dairy products. They are also abundant in oils acquired from tropical plants such as coconut and palm. Our bodies can synthesize saturated fats, so they are not needed in diet. Levels of "bad" cholesterol (there is good cholesterol as well) are in direct correlation with level of these fats in the organism.
Trans fats are manufactured from vegetable oils. Hydrogen is added to them in order to prolong their stability, which improves their transportation and re-usability properties. These fats are widely used in preparation of snacks, cakes, cookies, fried and baked goods, margarine and many other processed foods. These fats raise level of bad cholesterol and lower the level of good cholesterol. Also, these are basically a fat Frankenstein. Greatest danger from these fats lies in the fact that it can be used by body as replacement for good fats. This is an analogue of building an aircraft from defective parts and hoping for a safe flight.