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NEWSLETTER 13 - 1 : The Nature of Fat                                              (Edited: 9/14/03. Updated: 6/10/07)

Questions
The Fat Molecule
Fatty Acids
The Fate of Fatty Acids
Essential Fatty Acids
Trans-Fatty Acids
The Low Fat Hype

Questions

Why is fat bad?
What is a bad fat?
Can there be any good fat?
What makes a fat bad or good?
What is a saturated fat, an unsaturated fat, hydrogenated oils, a trans fatty acid, a fatty acid?
What is the difference between a fat and a fatty acid?
Is an oil a fat?

So many questions. Where are the answers? The answers are there. Follow the guide.

Yes, an oil is a fat, the only difference is that an oil is liquid at room temperature while a fat is not. This answers the last question.

You will find the answers to the others questions in the text that follows.

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The Template of a Fat Molecule

Elementary presentation of a 
									fat molecule

Figure 1:
All fat molecules are made from the same template
A short central element and three longer elements.

All fat molecules contain only carbon, hydrogen and oxygen atoms. All fat molecules are built from the same template: three longer pieces attached to a short central piece. The three longer pieces extend in space around the center piece as the spikes of a wheel. (In figure 1 the three long pieces are presented as if they were parallel to each other).

The central short piece has three carbon atoms. A string of 4 to 24 carbon atoms forms the core of the long pieces. The long pieces are "Fatty acids"

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The Description of a Fatty Acid

Palmitic Acid

Figure 2:
The fatty acid Palmitic acid has 16 carbons in a row. All fatty acids have a carboxyl group at one end of the molecule. Having no double bond between its carbon atoms, Palmitic acid is a saturated fatty acid.

Description

In a fatty acid molecule, the carbon atoms that form the spine of the molecule support each two hydrogen atoms. Exceptions are the carbons at the ends of the fatty acid molecule. The carbon at one end of the molecule supports three hydrogen atoms (At the left end in the drawing). The carbon at the other end of the molecule supports an oxygen atom and an oxygen/ hydrogen group (At the right end in the drawing).

The term "Fatty" comes to the molecule because the hydrogen cover of the carbon spine of the molecule repels water. The term "acid" comes from the existence at one end of the molecule (the right end in the drawing) of what is termed in chemistry a "Carboxyl group" which has acidic properties.

The molecule in figure 2 is a molecule of Palmitic acid. Palmitic acid is an example of a fatty acid with 16 carbons. Palmitic acid is also defined as a "16-0" fatty acid. In the abbreviation: "16-0", the first digits indicate the number of carbon atoms of the molecule (16 in this case), and the second digit indicates the number of double bonds (none in this case).

The numeric definition of fatty acids is much easier to remember than their common names or their chemical names. (The chemical name of Palmitic acid is "hexadecaenoic acid")

Palmitic acid has not one double bond and therefore it is termed a "Saturated Fatty acid"

Please note that the connection between the carbon of the carboxyl group and an oxygen atom is represented by a an equal sign. This equal sign is the representation of a double bond. The double bond in the carboxyl group does not account for the "saturation" of the molecule

See a the list of the nine most frequent saturated fatty acids occurring in human and in animal biology.

Variety in Length

Fatty acids vary in length by increments of two carbon atoms.

Stearic Acid

Figure 3:
Stearic acid is also termed 18:0, indicating it has 18 carbons and no double bond between its carbon atoms.

The molecule illustrated in figure 3 is a molecule of Stearic acid. Stearic acid is an example of a fatty acid with 18 carbons. Stearic Acid is also defined as a "18-0" fatty acid. Like Palmitic acid, Stearic acid is a saturated fatty acid.

Variety of structure

Fatty acids also vary by the absence or the presence of one or more double bonds between some of their carbon atoms.

Oleic Acid

Figure 4:
Oleic acid is a fatty acid with 18 carbons and one double bond between carbon 9 and carbon 10.
Oleic acid is also termed 18:1 n-9. In this formula "n-9" means that if you enter the molecule of oleic acid through its left end (the opposite from the carboxyl group), you have to progress to the ninth carbon to find a double bond between two carbon atoms.
The bending of the molecule results from the imbalance between the repulsive forces of the hydrogen atoms on both sides of the molecule.

Oleic Acid (Fig 4) is an example of a fatty acid with a double bond. Oleic acid is a Stearic acid that has lost one hydrogen atom at two adjacent carbons. In Oleic acid, the double bond is situated in the center of the molecule, between carbon atoms 9 and 10. The physical and the biochemical properties of Oleic acid differ from the physical and the biochemical properties of Stearic acid.

Oleic acid is a mono-unsaturated fatty acid."Mono" meaning "one " (double bond).

A double bond is very unstable. Light, heat, and oxidation molecules alter it.

See a list of the four most frequent mono unsaturated fatty acids occurring in human and animal biology.

Unsaturated fatty acids with more than one double bond are termed poly-unsaturated fatty acids. "Poly" means "multiple". (multiple double bonds).

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The Fate of Fatty Acids

The Storage of Fatty Acids

In human and in animal biology the storage of fatty acids occurs in two ways :

Fatty acids are stored attached three by three to a molecule of glycerol to form a fat molecule
Fatty acids are also stored two by two attached to a molecule of phosphoric acid to form what is termed a phospholipid.
Two phospholipid layers form the membranes of our cells and the membranes of the mitochondria and other cell components. In weight, phospholipids represent more than 65% of the membranes. See the illustration of the phospholipids from a cell membrane published in the web page of the Cell Biology Graduate Program from the University of Texas Medical Branch.

The importance of the type of fatty acid stored in the membrane phospholipids have only recently been understood. Example: The presence or the absence of long chain n-3 essential fatty acids in the membranes of the heart muscle cells makes the difference between life and death by cardiac arrest during cardiac overload.

The Turnover of Fatty Acids

The fatty acids that are stored in our body as fat or as cell membrane phospholipids are the subject of a constant turnover. Fat molecules and phospholipids are continuously broken down, and fatty acids are continuously assembled to form fat molecules and phospholipids.

The Synthesis of Fatty Acids

The fatty acids from food enter this carousel. This includes not only the fatty acids that we ingest under the form of fat, but also the fatty acids that our biochemistry makes. Indeed, we make our own fatty acids and we do this very efficiently. We make fatty acids by assembling building blocks of two carbon atoms.

The Elongation of Fatty Acids

Elongation Area

Figure 5:
The elongation of a fatty acid occurs always at the carboxyl end of the molecule.

We can add building blocks of two carbon atoms to existing fatty acid, resulting in the elongation of the molecule. The elongation occurs exclusively at the carboxyl end of the molecule.

The making of fatty acids and the elongation of fatty acids are enzymatic processes involving the addition of blocks of two carbons. The enzymes involved are the "Elongase Enzymes".

The enzymes involved are the "Elongase Enzymes"

The Desaturation of Fatty Acids

Not only do we synthesize fatty acids, we can also remove hydrogen atoms from fatty acids, resulting in all kinds of desaturated fatty acids. Oleic acid is made from Stearic acid by the removal of one hydrogen atom from the carbons 9 and 10. The carbon handles that held the two hydrogens cling to each other resulting in a double bond between the carbons.

The desaturation of fatty acids is also an enzymatic process.

The enzymes involved are the "Desaturase Enzymes"

See more information about the desaturation process

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The Essential Fatty Acids

Desaturase Area

Figure 6:
It is of particular interest to notice that the human desaturase enzymes operate only between the carboxyl group and carbon 9 of the fatty acids.

Like the synthesis and the elongation of fatty acids, the desaturation of fatty acids is also an enzymatic process. Human desaturase enzymes can only operate on the bonds between the first 9 carbons starting after the carboxyl group.

For human desaturase enzymes, the other carbons are out of reach. Which is to say that our food is the only supply of fatty acids with one or more double bonds in the out of range part of the molecule (the left end of the molecule in fig 4). Therefore, fatty acids with one or more double bonds in the out of range part of the molecule are termed Essential Fatty Acids (EFAs).

There are two categories of EFAs: The Omega 6 (n-6) and The Omega 3 (n-3) essential fatty acids.

The meaning of n-6 and of n-3

Meteorologists name their beloved hurricanes. Biochemists do the same with the atoms of their beloved molecules. They give them names. However, biochemists do not use full names, only letters of the Greek alphabet.

The first letter from the Greek alphabet alpha, goes to the carboxyl group carbon. Beta, the second letter goes to the second carbon, and so forth. An exception is the last carbon. The last carbon on the left end of the molecule received the name omega, the last letter of the Greek alphabet.

The term n-6 means that if one were to enter a fatty acid molecule through the left end of the molecule, the omega end, one would have to progress to the sixth carbon to find the first double bond. n-3 means the first double bond is after the third carbon.

The Main n-6 and n-3 EFAs

The prototype of the n-6 EFAs category is Linoleic Acid (LA) (18:2 n-6), , which is a 18 carbon molecule with two double bonds, one in position 6 (n-6 says it), and the second in position 9.

Linoleic Acid

Figure 7:
Linoleic acid (LA) (18:2 n-6) has two double bonds, the first one after carbon 6. Due to the repulsive action of the positive charges of the remaining hydrogen carbons the molecules has two bends. Oleic acid has only one.

See other members of the n-6 family

The prototype of the n-3 EFAs category is Alpha Linolenic Acid (ALA) (18:3 n-3) also a 18 carbon molecules this time with three double bonds, in position 3, 6, and 9.

Alpha Linolenic Acid

Figure 8:
Alpha Linolenic Acid (ALA) (18:3 n-3) bends more than Linoleic Acid.

See other members of the n-3 family

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Trans-Fatty Acids

In an usual unsaturated fatty acid, the missing hydrogens are on the same side of the molecule. Such a disposition is said a "cis" configuration. If the missing carbons are on the opposite sides of the molecule, the configuration is said to be "trans".

Trans-fatty acids occur naturally by a microbial activity on unsaturated fatty acids in then rumen of cows.
Trans-fatty acids occur readily during the industrial hydrogenation of unsaturated fatty acids.

The problem with trans-fatty acids is they do not fit in our biochemistry.
In the "cis" configuration (the normal configuration of an unsaturated fatty acid) the repelling action of the hydrogen atoms bends the molecule twice in the same direction. In the "trans" configuration the double bending occurs in opposite directions. This gives the molecule a "Z" twist..

Where are These Trans Fatty Acids?

Find out, courtesy of its author Richard Fang, in his database of Trans-Fatty Acids in Foods.

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The "Low Fat" Hype

Fats are said to contain too many calories, accused of clogging arteries and to be responsible for many health deteriorations. Those allegations have initiated the actual low fat diet hype. A low fat diet and exercise are regarded as paramount to good health.

The "Low Fat" hype pushes grocery stores to offer more and more products manipulated to remove part or all of the fat they contain.

As a consumer of plain yogurt, I have witnessed the progressive disappearance over time of plain yogurt varieties from the shelving and their replacement by an increasing number of low fat and fat free yogurts.
An argument of the low fat promoters is that fat contains to many calories. Calorie counters beware! Fat free yogurt may contain more calories per serving than plain yogurt!.Because of the added sugar. Why do they add sugar? To mask the bad taste of fat free yogurt!


Low fat diet promotors also make a distinction between saturated fats and unsaturated fat in food. Saturated fat is evil, unsaturated fat is less.

The food label legislation follows this trend and the food industry has to label its products accordingly, indicating the percentages of calories from fat and the percentage of calories from unsaturated fat.

The low fat hype still intoxicates the public and it is going to take a while to redirect the public opinion.

Read More :  The Role of Essential Fatty Acids in our biochemistry.

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