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
-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
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.
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.
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
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 are discussed in more detail here.
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