In recent years fat has become the focus of countless articles, books, diet plans, and advertising claims, many of which give the false impression that fat is the ultimate dietary villain, to be avoided at all costs. While it is true that excess fat in the diet is unhealthy because it raises the risk of coronary artery disease, obesity, and certain cancers, it is still an essential nutrient that provides energy and fulfills vital bodily functions. Fat is essential in making the fat-soluble vitamins A, D, E, and K available to our bodies. Fat is digested slowly, providing a lasting sensation of fullness (known as satiety), and slows the digestion of carbohydrates and protein ingested along with it, thus giving the body time to absorb the nutrients contained in foods. Lastly, fat has a crucial role in the development of flavor in cooking.
Fats are grouped into three main categories according to their degree of saturation, a term that refers to the molecular structure of the fat. A single fat is actually a number of chains, known as fatty acids, composed of carbon, hydrogen, and oxygen linked together. The individual fatty acids can be saturated, monounsaturate, or polyunsaturated, depending on how many open sites there are for hydrogen atoms to bond with a carbon atom. Saturated fatty acids cannot accept any more hydrogen, monounsaturated fatty acids have one open site on the chain, and polyunsaturated fatty acids have more than one site open.
Current dietary recommendations are that fat should account for 30 percent of calories at most, and most of the fat should be mono- and polyunsaturated. Saturated fats should not exceed 10 percent of total daily calories because they have been shown to have an adverse effect on serum cholesterol levels. In a 2,000-calorie diet, these limits translate to approximately 600 calories from all fats (about 67 grams), with no more than 200 of these calories (22 grams) coming from saturated fats.
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The Professional Chef, 7th Edition by The Culinary Institute of America