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Let's look at the sources, functions and requirements of macronutrients first. Macronutrients are the nutrients that are needed in relatively large amounts (gram quantities/per day). They are fats, proteins, and carbohydrates. All are hydrocarbon chains, with protein having additional nitrogen attached to the molecules. Proteins and carbohydrates burn approximately 4 kilocalories per gram while fats burn approximately 9 kilocalories per gram, over twice as much energy released per gram equivalent. Macronutrients are also known as energy nutrients for this reason.
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Fats are hydrocarbon chains that either have single bonds (saturated), contain one double bond (monounsaturated), or more than one double bond (poly-unsaturated). The more double bonds that are present, the more unstable the molecule, and the more likely that rancidity can occur, releasing oxygen free radicals that may damage cells.
Fat is not the "villain" that it is often made out to be by the popular press. Fat functions in the body in a variety of ways. In general, it serves as a cushion for vital organs, insulation for protecting the body against extremes in temperature, a transport medium for fat soluble nutrients, an intermediary in hormone production, an important energy reserve source, a lubricant, a source of essential fatty acids, and adds palatability to many foods.
Saturated fats are very stable and are solid at room temperature. Example sources of saturated fats include butter, coconut, whipped cream and lard. They are, however, responsible for raising blood cholesterol levels and therefore are not recommended sources of fats to be consumed in high quantities. The American Heart Association recommends that saturated fat consumption be limited to no more than 7% of calories in the diet. When you consider that a teaspoon of fat contains 5 grams, and the number of grams of saturated fat recommended in a 2000 kcal intake is 13 grams (2000 x .07 = 140 kcals divided by 9 kcals/gm = 15.56 gms or 16 gms), it doesn't take much to reach that level!
Monounsaturated fats are liquid or gel-like at room temperature, and are fairly stable. Common sources of monounsaturated fats include olive oil, avocados and peanuts. Monounsaturated fats lower LDL blood cholesterol, increase HDL cholesterol and therefore are considered beneficial in the diet. In addition, some studies suggest that monounsaturated fats may have a protective effect in regard to the development of breast cancer. The "Mediterranean" diet consists of large quantities of unsaturated fats, mostly in the form of olive oil, used in cooking and added to salads and used as spreads on breads and in pastas. The American Heart Association recommends that total fat consumption be limited to no more than 30% of calories in the diet, the majority of it coming from sources high in monounsaturates.
Polyunsaturated fats are liquid at room temperature and are unstable, therefore susceptible to oxidative rancidity. This is one reason why vegetable oils are hydrogenated; the destruction of the double bonds with saturation with hydrogen enable the fat to have a longer shelf life. Unfortunately though, the process which the oils undergo to increase stability, causes a configuration of trans fatty acids to form. Trans fatty acids are now thought to be unhealthy in regard to their effects on blood cholesterol. Examples of hydrogenated fats are vegetable shortening and stick (solid) margarine. Sources of polyunsaturated fats include corn and soybean oils.
The American Heart Association recommends that polyunsaturated fat consumption be limited to no more than 7% of calories in the diet. Why so low? A couple of reasons: first, even though polyunsaturated fats lower blood cholesterol levels, they also lower the HDL fraction; second, because of their unstable nature in regard to their propensity to form free radicals that can damage cells, they are considered to be mutagenic and may increase the risk for the development of various types of cancer when ingested in large quantities.
AHA Dietary Strategies to Reduce Risk of Coronary Heart Disease
Nutrient Recommendations Examples Total Fat 30% or less of total kcal Saturated < 7% of total kcal meat, butter, whole fat dairy Polyunsaturated < 7% of total kcal corn oil, commercially baked goods Monounsaturated up to 15% of total kcal avocado, nuts, olive oil
You can calculate your daily recommended fat consumption by filling in your daily calorie intake and pressing the calculate button below.
Content questions should be directed to: Marilyn.S.Edwards, Ph.D., R.D.
or Maggie McQuiggan, M.S.
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