The common type of fats that fall into the bad fats category is saturated and trans fat. Trans fat are considered the worst offender because of the health problems that can be cause by consumption of trans fat. Trans fat are manufactured and not natural. Hydrogen is added to polyunsaturated fats at room temperature to make them solid. When looking at the ingredients list trans fats are often labeled as “Partially Hydrogenated Soybean Oil” or another variation of that, but looking for the word Hydrogenated is a clue that it contains trans fats. Some of the negative health problems associated with trans fat are affects immune response, negatively affects cholesterol, increases blood insulin levels in response to glucose, and many other problems (Journal of AHA). Most processed food will contain trans fat so it is best to avoid trans fat whenever possible.
Good fats are the type of fat that should make up the majority of daily dietary fat intake. Within the category of good fats there are two types of fat, monounsaturated fats and polyunsaturated fat.
Polyunsaturated fats are also naturally occurring and can be found in foods such as salmon, herring, mackerel, halibut, and other fishes, soybeans, fish oil, etc. Similar to monounsaturated fats, polyunsaturated fats have been show to lower total cholesterol and LDL cholesterol. A British study done in 2005 showed that an increase in consumption of polyunsaturated fat helped lower the risk for CHD (Coronary Heart Disease) (Zatonski). It has become clear that consumption of healthy fats will lead to a better quality of live than if one consumed predominantly unhealthy bad fats in their diet.However, there is also discussion about the importance of the omega 6 to omega 3 ratio in diets. A quote from a research article sums up the position good, "Western diets the ratio is 15/1-16.7/1. Western diets are deficient in omega-3 fatty acids, and have excessive amounts of omega-6 fatty acids compared with the diet on which human beings evolved and their genetic patterns were established" (Biomed Pharmacother). It has been speculated that an increase in polyunsaturated omega 6 "promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases," (Biomed Pharmacother). The article also suggests that a ratio of 4:1 (omega 6:omega 3) would be more favorable in the prevention of diseases. It is easy to see how something as simple as fat can turn into a complex issue with multiple areas that need to be investigated.
Biomed Pharmacother. 2002 Oct;56(8):365-79.
Zatonski, W; Willett, W. Changes in dietary fat and declining coronary heart disease in Poland: population based study. British Medical Journal. July 23, 2005. 331:187-188.