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Fats: Triglycerides, Free Fatty Acids and Sterols Also Called "Lipids" |
Fat is a term that describes a large number of different dietary compounds that have in common that they are not at all soluble in water but are soluble in organic liquids like ether. This common property derives from the fact the main chemical structure of fats is called a "hydrocarbon" and consists of long chains of carbon atoms bonded to each other with hydrogen atoms attached on the side. These bonds also contain a relatively large amount of energy which accounts for the high calorie density of fat. Basic Properties of Fats -Fats are insoluble in water -Fats have about 9 kilo-calories (dietary calories) per gram -Because fats can store a lot of energy, they generally are used to do just that: as adipose tissue in animals and in seeds for plants. -Fat also plays a structural role: as thermal insulation and cushioning for delicate organs. -Fat is much less dense than lean tissue (about 0.9 grams/cc for fat and 1.10 grams/cc for lean) -Dietary fat is the most 'filling' macronutrient although its high calorie density and low thermic effect generally make fat reduction an important part of any weight control diet. Dietary fat is classified into a variety of different types: fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, saccharolipids, and polyketides. For the purposes of this discussion, we'll concentrate mostly on fatty acyls (fatty acids), glycerolipids (including triglycerides) and sterols. Triglycerides Triglyceride" describes a form of fat commonly found in nature wherein three fatty acid molecules are chemically bonded to the molecule called glycerol (gylcerine). Triglycerides cannot be directly absorbed by the human small intestine and instead must be broken down by pancreatic enzymes called lipases into glycerol and three free fatty acids. Once free fatty acids have been absorbed from the gut, they are either directly burned for energy or converted back into triglyceride and transported by proteins to lipocytes (fat cells) for storage. Fatty Acids: As described above, fatty acids are the building blocks of tiglyceride and among the products resulting from the action of pancreatic lipase upon triglyceride. Fatty acids are also found in foods in their free-form and are called, appropriately enough, free fatty acids. Saturated, Mono-Unsaturated, Polyunsaturated and Trans-Fatty Acids: These terms refer to the precise structure of the hydrocarbon tails of fatty acids and specifically to wether those tails contain any carbon to carbon "double bonds" and if so, the number and the orientation of the bonds. These details alter the effects of dietary fats upon human cardiovascular health although all of these varieties of fats still have the same caloric densities and low thermic effects as any fat. Saturated Fatty Acids "Saturation" is an organic chemical term. It basically means "saturated with hydrogen" or alternatively, "the absence of carbon to carbon double bonds". Saturated fats have higher melting temperatures and many of them are solid at room temperature. They are also less likely to go "rancid" from oxidation at high temperatures and are therefore often used for deep-fat frying. Saturated fats generally increase human cardiovascular disease risk by raising serum levels of another fat called cholesterol. This is true wether the fatty acids are "free" or part of a triglyceride molecule. Mono & Polyunsaturated Fatty Acids Unsaturation refers to fatty acids with double bonds in the hydrocarbon tail. Monounsaturated fatty acids obviously have just one double bond whereas polyunsaturated fats have more than one. The more unsaturated a fat is, generally the lower its melting point. Unsaturated fats tend to have either a neutral or even slightly beneficial direct effect on human cardiovascular risk. Trans-Fatty Acids: Trans-fatty acids are discussed in more detail here. |
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