Fats primarily divide into three different categories – saturated, unsaturated, and trans fat.
Saturated fat is fat that is naturally SOLID AT ROOM TEMPERATURE. Examples of saturated fat include butter, cheese, the marbling in beef, and the fat in chicken. Saturated fat comes primarily from animal sources and consuming diets high in saturated fat increases LDL levels (the bad type of cholesterol).
Unsaturated fats are naturally LIQUID at room temperature. Examples of unsaturated fat include olive oil, canola oil, the oils in nuts and seeds and the oils in fish and in avocados. Unsaturated fats generally come from vegetarian sources and tend to increase HDL levels (the good form of cholesterol) and to lower LDL levels (the bad cholesterol) (so there’s a double benefit). In general, doctors recommend that patients should favor the consumption of fats in this category.
Trans fats are fats which are normally liquid at room temperature, but have been chemically modified to be solid at room temperature through the process of hydrogenation. Trans fats are used in food manufacturing to improve the shelf life of various food items, and to enhance taste and texture. Trans fats are frequently found in processed foods, including margarine. Trans fats tend to raise LDL levels and lower HDL levels (a double whammy) – and therefore it is recommended that consumption of trans fats be completely avoided. Indeed, there are no known safe levels for trans fat intake. The best way to know if what you are eating contains trans fats is to check the label. Look for any “hydrogenated” or “partially hydrogenated” items in the ingredient list. Even if the label says “no trans fats”, by law small amounts may still be present – the only way to be sure that the product does not contain ANY trans fats is to NOT see “hydrogenated” or “partially hydrogenated” in the ingredient list.
In summary, the most healthful fats are unsaturated. These are liquid at room temperature and come from vegetarian sources. Saturated fats come from animal sources and are solid at room temperature. Saturated fats, because they raise LDL levels should be limited. Trans fats are artificially modified fats and should be avoided altogether. There are no safe levels for trans fat consumption.