Fat is found both in the foods we eat, called dietary fat, and in our bodies in the form of depot fat. Fats provide the most concentrated form of energy, and contain 9 calories per gram as compared to 4 calories per gram for both carbohydrate and protein. Common sources of dietary fat include meats, dairy products such as milk, cheese and butter, eggs, cooking oils, mayonnaise and nuts.
There are basically two types of dietary fats: saturated and unsaturated.
Saturated fats, including trans fat, are generally solid at room temperature and, except for a limited number of plant sources such as coconut oil and palm oil. Saturated fats increase LDL cholesterol (unhealthy cholesterol,) which can increase your risk of cardiovascular disease. Trans fats occur naturally in some foods, especially food from animal sources, but most trans fats are made during food processing through partial hydrogenation of unsaturated fats. This process creates fats, termed industrial or synthetic trans fats, that are easier to cook with. Research shows that synthetic trans fat can increase unhealthy LDL cholesterol and lower healthy high-density lipoprotein (HDL) cholesterol, which can increase your risk of cardiovascular disease.
Unsaturated fats are usually liquid at room temperature and include monounsaturated fats such as olive and canola oil, nuts, avocados and olives and polyunsaturated fats such as Omega 3s, derived from fatty fish, fish oil, soybeans, tofu, walnuts and flaxseed and Omega 6s which are abundant in Western diets and include mayonnaise, salad dressing, and corn oil. Omega 3s are recommended because of their anti-inflammatory effects. Because saturated fats have been linked to elevated cholesterol and other health problems, unsaturated fats are preferred.
Dietary fat is necessary for a number of functions, including building cell membranes, the formation of both vitamin D and cholesterol, and the development of hormones. Fat also acts as padding and insulation for the body, but the primary purpose of dietary fat is to provide energy, especially stored energy.
It should be noted that an excess of fat in the diet can lead to a number of medical problems, including obesity, heart disease, and certain types of cancer. Another problem is that dietary fat tends to lead to depot fat. Not only does fat contain more than twice the calories of either protein or carbs, there is evidence to suggest that excess fat calories are more readily stored as body fat than either excess carbohydrates or protein.
How much fat should the average person consume? It is recommended that dietary fat be limited to approximately 20% of the total daily calories with less than 10% of calories derived from saturated fats.