Properties of Fats
How Normal Fats are Digested
How Normal Fats are Absorbed
How Olestra is Digested and Absorbed
Olestra and Gastrointestinal Problems
Olestra and Vitamin, Mineral, and Water Absorption
More on Olestra
Works Cited

Properties of Fats

Normal Fats

Fats fall under the broader category of lipids. Lipids are generally insoluble in water and contain varying numbers of chains called fatty acids. Fatty acids are carbon chains, usually 16, 18, or 20 carbons long, with double bonds in the chain. The number of carbons in the fatty acid and the number of double bonds found in the chain are highly variable. Saturated fats are formed from fatty acids without any double bounds. These chains can be packed tightly together resulting in a higher boiling point temperature. This differs from unsaturated and polyunsaturated fats which have one or more double bonds and make kinks in the fatty acids chains. These kinks prevent chains from packing together closely, significantly lowering the melting point of unsaturated fat deposits and rendering membranes made of unsaturated fats to be more flexible and mobile (Banks 1976). We will return to the melting points of fatty acids later on this page.

A saturated fatty acid. Figure by Megan Castle.

Lipids include cholesterol, which are based on a phenanthrene ring structure, and phospholipids with the characteristic hydrophobic and hydrophilic ends. A third group of lipids consists of mono-, di- and triglycerides. This group is made of one, two, or three fatty acid chains attached to the hydroxyl groups of glycerol (McMurray 1983). Since triglycerides (three fatty acid groups) are commonly ingested and absorbed and are the major source of energy for the body, we will follow this fat’s chemical digestion process.

A tryglycerol. Figure by Megan Castle.

Indigestible Fats

Olestra is made of fats with six, seven, or, most often, eight fatty acid chains attached to a sucrose molecule. It is formed by binding fatty acids found in edible fats and oils, like soybeans, maize, coconut and cottonseed, with carbon chain lengths of eight to twenty-two carbons to sucrose molecules (Institute of Food Science and Technology 2004, http://www.ifst.org/hottop13.htm.) Olestra molecules, sometimes referred to as octa-esters because of their characteristic 8 fatty acid chains, are made to smell, taste, and have the same consistency of triglycerides so that consumers cannot distinguish between foods made with olestra or those made with traditional cooking fats (Jandacek 1999). To mimic the characteristics of natural fats, the makers of olestra use fatty acids of similar lengths and saturation (number of double bonds) of those found in triglycerides used for cooking (Institute of Food Science and Technology 2004, http://www.ifst.org/hottop13.htm).

Space filling model of olestra.  We show a model of sucrose with eight oleic acid ester groups.  The fat substitute compound will have a mixture of many similar molecules. Copyright © 1997 by Daniel J. Berger. This work may be copied without limit if its use is to be for non-profit educational purposes. Such copies may be by any method, present or future. The author requests only that this statement accompany all such copies. All rights to publication for profit are retained by the author.


As stated above, the properties of fatty acid chains determine the melting point of the fat. Olestra can be made with different lengths and saturations of fatty acids. If highly saturated fatty acids are used to make olestra, then that type of olestra will have a high melting point whereas fatty acids that are unsaturated will have lower melting points. Melting points of olestra that range below room temperature (about 22 degrees C) are considered liquid, melting points between room temperature and body temperature (37 degrees C) are considered semisolid, and above body temperature are solids. The production of olestra must be measured by two standards. The first is the taste of the product; olestra must have as similar a taste and texture to triglycerides as possible in order to please consumer tastes. This means using fatty acids that are found on the glycerols of triglycerides, which may make olestra be solid or liquid at room or body temperature, depending on the fatty acid used. If the fatty acids used to make olestra are solids around the same temperature as normal body temperature, then the texture of olestra is different from triglycerides, resulting in an undesirable, greasy, oily, or waxy feel in the mouth. The second standard is gastrointestinal comfort. If the fatty acids are liquid at body temperature, then there is more of a chance that during digestion, the olestra, which is not absorbed or broken down by the body, will separate from fecal material and remain in a liquid state causing oil leakage (Jandacek 1999.) The properties of olestra impose a fine line for makers between consumer taste and digestive symptoms. Iin order for olestra to be a successful product, producers must balance between the two factors above.

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