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(You may click on any of the above, all are links that will take you directly to that section.) The goal of this approach is to present you, the reader, with a easy way to understand and remember which fats are bad and why. What are Fats?Fats are naturally occurring organic chemical compounds that can be and often are modified by chemical processing. All fats have some common characteristics that identify them; they also have differences, which are very important because they determine how they are utilized or metabolized by humans. Knowing something about the chemical structure of a fat molecule is very important, for fat naming conventions depend on its structure. Furthermore, fats with similar structures will have the same effect in our metabolism--the trick is to learn what structures are important for our metabolism. To help us understand the the structure of fat, we will examine two different fat molecules, butyric acid (one of the fats in butter that gives it its characteristic flavor) and olive oil, emphasizing the differences that result in their being metabolized differently by humans. Any fat molecule, also known as a fatty acid, has:
(To refresh your organic chemistry, a carbon atom has 4 bonds, a hydrogen atom 1 bond, and an oxygen atom 2 bonds. These atoms can be combined in a myriad of ways, which makes organic chemistry so fascinating and complex--however all the atoms in any stable organic molecule must have all their bonds interconnected in some fashion.) Our first example of a typical fat molecule is butyric acid. Butyric Acid Fats can differ in 4 ways, any one of which can give it completely different characteristics:
Olive oil, another fatty acid that will be discussed next, has some of the above differences when compared to butyric acid. Olive Oil Saturated Fats--Bad ActorsA fat is defined as saturated if every hydrocarbon in the chain has as much hydrogen bound to it as it can (in other words, if there is no double-bond between any hydrocarbon in the chain, which structure allows the fat molecule to be "saturated" with as much hydrogen as it can hold). Butyric acid, which is illustrated above, is a saturated fat since it has no double-bonds; olive oil is an unsaturated fat because it has a double-bond (olive oil would become a saturated fat if the double bond were replaced with 2 hydrogen atoms). Saturated fat comes from two primary sources:
Reputable scientists and doctors today believe that saturated fat is not good in human diets because it raises total blood cholesterol. The American Heart Association currently recommends that individuals with coronary heart disease limit their intake of saturated fat to less than 7% of their daily total caloric input1. Unsaturated Fats--the Good GuysLikewise, unsaturated fats are named because of their chemical structure. A fat is defined as unsaturated if it has at least one double-bond in the hydrocarbon chain. This double-bond results in less hydrogen in the chain than if there were no double-bonds. Hence, the chain is unsaturated with respect to the maximum hydrogen that could be present. Olive oil, discussed above, is an unsaturated fat. There are two major types of unsaturated fats, most of which are liquid:
Both the American Heart Association and the US Food & Drug Administration highly recommend that everyone use mono-unsaturated and poly-unsaturated fats in their diets instead of saturated fats. It is important that these unsaturated fats have not been hydrogenated in any fashion (discussed in more detail below). These unsaturated fats may help lower your blood cholesterol when taken instead of saturated fats in your diet. Again, a moderate intake of all types of fat is best; remember a teaspoon of any fat equals 35 calories.2 Hydrogenated & Partially Hydrogenated Fats--More Bad ActorsThe above mono- and poly-unsaturated fats can be processed chemically to add hydrogen atoms to replace the double bonds existing between their hydrocarbons. This process, which takes place in the presence of heat, pressurized hydrogen, and a metal catalyst is called hydrogenation. The visible result of this process is that a liquid fat is turned into a solid fat. Food products containing hydrogenated fats have improved shelf-life and flavor-stability when compared to products containing pure unsaturated fats, which when exposed to air oxidize creating compounds that have rancid, stale, or unpleasant odors or flavors. Also, fats that are fully hydrogenated are too waxy or solid to use as food additives, so manufacturers instead use partially hydrogenated oils. These oils are produced using the hydrogenation process described above, but the process is stopped when the fat reaches the proper consistency for its application. An example of a partially hydrogenated fat is Crisco© shortening. Hydrogenated fats are obviously bad in our diet because they contain saturated fats. Partially hydrogenated fats are doubly bad in our diet because they contain not only saturated fats, but also a substance called "trans fats", discussed in the next section. Trans Fats--Really Bad ActorsThe partial hydrogenation process does one other very important thing to unsaturated fat molecules: it changes the configuration of many of the unsaturated fat molecules from the more prevalent Cis configuration as shown below on the left to the Trans configuration on the right.
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Cis-9-octadecenoic
acid
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Trans-9-octadecenoic
acid Shown is a mono-unsaturated fatty acid, in this example 9-octadecenoic acid
(olive oil),
that has a double bond near the middle of the hydrocarbon chain.
This double bond appears as a black "=" in these molecules;
carbon atoms are shown in gray, hydrogen atoms in blue, and oxygen atoms
in red. The Cis configuration is very common in any
unsaturated fat that has not been subjected to the partial hydrogenation
process; the double-bond binds the carbon atoms tightly and prevents the
rotation of the carbon axis along the bond axis. The partial
hydrogenation process converts the commonplace Cis configuration into
the Trans configuration. The Trans configuration allow
the fat molecules to lie closer together and become solid rather than
liquid.3 |
Unsaturated fats that have the trans configuration are defined as "Trans Fats". It should be noted that the biggest source of trans fats in the American diet comes from partially hydrogenated unsaturated fats. These trans fats are almost always used in the preparation of food products like French fries, cookies, crackers, donuts, the "stuff" in Oreos©, margarine, Crisco© shortening, and white bread. Trans fats are used in these products because they give them very long shelf-life coupled with the "correct" taste. Trans fats also occur in nature as the result of anaerobic bacterial fermentation in ruminant animals. (For those who don't live on a farm, a ruminant animal is one that chews its cud and has a complex, 3 or 4 chambered stomach.) These trans fats enter the human food chain as meat and dairy products.4 All trans fats, from any source, are considered very bad in our diet, for they:
Starting January 1, 2006, all foods sold in the the United States will have to list the amount of trans fat they contain right below the amount of saturated fat on their Nutrition Facts label. Note that on this label there is no % Daily Value amount listed in the column for Trans Fat--it's that way because there is none recommended for human consumption. The trans fat listed on this label is in addition to the saturated fat--it is not a part of saturated fat. Omega-3 & Omega-6 Fats--More Good GuysOmega-3 and Omega-6 are unsaturated "Essential Fatty Acids" (EFAs) that need to be included in the human diet because our metabolism cannot create them from other fatty acids. These fatty acids all have double bonds with the Cis configuration; the number 3 or 6 refers to the distance of the first double bond in the hydrocarbon chain counting from the last hydrocarbon in the chain (the one furthest from the carboxyl group, also known as the "omega" hydrocarbon).
So, What Does This All Mean?Let's summarize what we have learned, applying it to our diets:
Finally, for recommendations as to the amounts of fat, both the good guys and the bad actors, to have in your diet, the advice of your physician must be followed, especially if you have coronary artery disease. The Cardiac Therapy Foundation offers its members the opportunity to meet with its Registered Dietitian, Sarah Ellis. Make use of her knowledge and resources to help you follow your physician's advice. ------------------------------------ References: 1. http://www.americanheart.org/presenter.jhtml?identifier=532 2. http://www.fda.gov/fdac/features/2003/503_fats.html 3. http://www.scientificpsychic.com/fitness/fattyacids.html 4. http://circ.ahajournals.org/cgi/content/full/95/11/2588 5. http://www.americanheart.org/presenter.jhtml?identifier=3006581
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As the title
of this web page suggests, the word "fat" has a variety of meanings:
gregariousness, obesity, excesses, and, of course, the fat we eat.
Most meanings connote some form of overindulgence. Here we will
concentrate on just one of those meanings: the fat we eat, which is
an essential component of our diet that needs to
be understood and controlled, especially by those who have
coronary artery disease. Fat is the most concentrated source of
calories in our diet: one tablespoon of
fat--any type of fat--contains about 135 calories; in contrast a
tablespoon of sugar contains only about 48 calories.
Obviously, the misuse of fat can have adverse consequences!
To
the left is illustrated the chemical
structure for butyric acid.
At
the right end of this molecule, shown in
red, is the carboxyl group, which is always located at the
far end of the hydrocarbon chain. Butyric acid has 3 hydrocarbon groups, shown in blue, attached in a chain to
the carboxyl group. The chemical bonds that hold the groups together
are shown in black; bonds within a group are shown in that group's
color. All bonds in the hydrocarbon chain are single-bonds, shown
by a single line.
To the left is
illustrated the chemical structure for olive oil.
This molecule
differs from butyric acid in two ways. There are
17
hydrocarbon groups in this molecule; and one of the bonds, located 9
groups away from the "omega" end, is a
double bond, shown by an "=" sign. Whenever
a double-bond occurs, the hydrocarbon
group on either side of this bond has only
one hydrogen atom each
instead of two. These two changes are all that it takes to give us
olive oil instead of butter!
