Fat forms part of a healthy diet. But the type of fat you include is very important. Saturated fats are generally unhealthy, while unsaturated fats are much better.
Eating saturated fats raises levels of LDL ("bad") cholesterol; hence too much of these in the diet is harmful.
Saturated fats come from animal fats, e.g. meat, lard and dairy products. They also come from the so-called tropical oils, e.g. palm and coconut oil.
These fats are useful in foods because they are hard at room temperature and are stable for relatively long periods of time. They don’t become rancid as fast as the more liquid, unsaturated fats.
Mono- and polyunsaturated fats are much better for you than saturated fats. In fact eating certain polyunsaturated fats can actually decrease your total cholesterol levels.
Mono- and polyunsaturated fats are found in vegetable oils. Because they are all very liquid and rather unstable, the food industry resaturated these fatty acids by adding back hydrogen and breaking the double carbon–carbon bonds, a process called hydrogenation.
Most of the vegetable fats we eat in margarines and other oils are partially hydrogenated to make them less liquid. The more solid the margarine the more hydrogenated the fat and the less “healthy” it is.
The problem with the hydrogenation process is that it makes an unsaturated fat behave more like a saturated fat with all the resultant health problems.
(The Heart and Stroke Foundation/Health24)