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Fats are one of three nutrient groups that provide energy for the body (the others are protein and carbohydrates). Fats are also called lipids.
Fats provide 9 calories per gram.
Fats are triglycerides. They consist of a glycerol molecule and 3 fatty acid chains. The fatty acid chains are chains of carbon atoms with hydrogen atoms attached. One end of the fatty acid chain terminates with an acid molecule (carboxylic acid COOH) and the other end with a methyl group (CH3).
Most naturally occurring fatty acids contain even numbers of carbon atoms. There are many different fatty acids with lengths varying between 4 and 24 carbon atoms.
The carbon atoms in the fatty acid molecule can be connected with single or double bonds. Fatty acids that contain all single bonds are called saturated because they contain the maximum number of hydrogen atoms. Each carbon atom (except the ones at each end) connects to 2 other carbon atoms and to 2 hydrogen atoms.
Fatty acids that contain one or more double bonds are called unsaturated. Those with one double bond are called monounsaturated. Those with two or more double bonds are called polyunsaturated. In this case, each carbon atom involved in a double bond connects to 2 other carbon atoms and to only 1 hydrogen atom. The double bond replaces the bond the carbon would have with a hydrogen atom. Double bonds never occur at the ends of the fatty acid chain.
Each double bond in an unsaturated fatty acid represents 2 missing hydrogen atoms (one for each of the carbon atoms involved in the double bond).
There are 2 physical configurations for the remaining 2 hydrogen atoms in the double bond. If the 2 hydrogen atoms are physically on the same side of the carbon atoms the bond is said to have cis configuration. If the 2 hydrogen atoms are on opposite sides of the carbon atoms the bond is said to have trans configuration.
The cis configuration is more prevalent in nature. Most animal and vegetable fats have the cis configuration. A small number of trans fats occur naturally. Most trans fats are produced by the process of hydrogenation, described below.
Note that the trans configuration describes a double bond. This means all trans fats are unsaturated fats.
Physical Properties of Fatty Acids
Saturated fats tend be more solid than polyunsaturated ones. Polyunsaturated fats are more liquid (i.e., oils). Generally, the more saturated a fat, the more solid it is. In addition, longer fatty acid chains tend to be more solid than shorter ones.
In general, animal fats are more saturated (and more solid) than vegetable oils. However, some vegetable oils such as coconut and palm oils are saturated. They tend to be liquid because their fatty acid chains are shorter.
Fatty acids with cis double bonds have a bent shape, and so tend to pack more loosely, and so are less solid. Fatty acids with trans double bonds are straighter and tend to pack tighter, and so are more solid.
All fats break down when exposed to oxygen. Fat oxidation causes fats to become rancid. Double bonds are less stable than single bonds, so unsaturated fats tend to spoil more easily.
To make fats more stable (less prone to spoilage), and to make them more solid, manufacturers add hydrogen to fats in a process called hydrogenation. This process converts some of the unsaturated double bonds into saturated single bonds. Such fats are usually listed as "partially hydrogenated" on product labels.
The process of hydrogenation causes some of the cis double bonds to shift into the trans configuration. For this reason, partially hydrogenated vegetable oils are sources of trans fats.
Health Effects of Saturated and Trans Fats
Studies have shown that diets high in saturated fats can cause elevated levels of LDL (bad) cholesterol and lower levels of HDL (good) cholesterol. These effects increase the risk of heart disease and stroke.
The Nutrition Labeling and Education Act (NLEA 1990) has required that saturated fat be listed separately on Nutrition Facts labels since May, 1994.
More recent studies have shown that trans fats have a similar effect on cholesterol levels. The FDA (US Food and Drug Administration) has revised the nutrition labeling regulations to require that trans fats also be listed separately on Nutrition Facts labels. Trans fats are required on labels after January 1, 2006.
Fatty acids are described by listing the number of carbon atoms and the number of double bonds, separated by a colon. For example, oleic acid is 18:1. This means it has 18 carbon atoms, with one double bond. This is a monounsaturated fatty acid.
There are 2 isomers of oleic acid. Isomers are molecules that have the same chemical composition but different physical configurations. In this case the isomers are either cis or trans. The terms cis or trans are added to the fatty acid names, so the isomers of oleic acid are written as 18:1 cis or 18:1 trans.
Polyunsaturated fats have multiple double bonds. There can be a combination of cis and trans bonds in the same fatty acid. In this case a single letter "c" or "t" is used to indicate each type of bond. For example, isomers of linoleic acid can be written as 18:2 cc or 18:2 ct or 18:2 tc, etc.
Finally, the position of the double bonds in the fatty acid can be indicated with the letter "n" followed by the position of the double bond. For example, oleic acid has its double bond at the ninth carbon atom (counting from the methyl group end), so could be written as 18:1 n9 cis or 18:1 n9 trans.
Many of the fatty acids have historically been assigned names as they were discovered. nutraCoster lists the names of the fatty acids when they are available.
Omega-3 and Omega-6 Fatty Acids
The methyl group end of the fatty acid is called the omega end (omega is the last letter of the Greek alphabet; the methyl group is the end of the fatty acid). When the position of the first double bond is located 3 carbon atoms from the omega end, the acid is called an omega-3 fatty acid. When the first double bond is located 6 carbon atoms from the omega end it is called an omega-6 fatty acid.
Omega-3 and Omega-6 fatty acids play an important role in human nutrition. The body cannot synthesize these fats; they must be supplied by the diet. Because of this they are known as essential fatty acids.
Omega-3 fatty acids have important anti-inflammatory properties and are thought to be important to help prevent heart disease and stroke. They are also important for infant growth. Fish oils and vegetable oils are important sources of omega-3 fatty acids.
The following table lists some common omega-3 and omega-6 fatty acids:
Summary and Detail Information
nutraCoster lists several levels of detail for fats. For example, Total Fat consists of Saturated Fat, Monounsaturated Fat, Polyunsaturated Fat and Total Sterols.
In turn, Saturated Fat consists of the sum of all of the n:0 fatty acids. Finally, some of the individual fatty acids consist of the sum of the different isomers listed.
The following table lists the summary and detail information tracked by nutraCoster. Note that some values, like Total Saturated Fat, are both summary and detail information.
* Fatty Acid 18:2 other consists of unspecified linoleic acid isomers.
Total Trans Fat consists of each of the individual trans fatty acids. The following table lists the trans fatty acids totaled to calculate Total Trans Fat.
In general, the sum of the detail values should equal the summary value. The Detail Consistency table on the Carbohydrates page shows the deviation of the detail totals from the summary values.
Total Omega-3 Fat consists of each of the individual omega-3 fatty acids. The following table lists the omega-3 fatty acids totaled to calculate Total Omega-3 Fat.
Total Omega-6 Fat consists of each of the individual omega-6 fatty acids. The following table lists the omega-6 fatty acids totaled to calculate Total Omega-6 Fat.
Entering Detail Values
When you enter or change any of the detail values, nutraCoster checks to see if the associated summary value was equal to the sum of the detail values before the change. If so, nutraCoster updates the summary value to agree with the sum of the detail values after the change. If not, nutraCoster does not update the summary value.
Example: The value for Total Fat is 10 g, and the value for Total Monounsaturated Fat is also 10 g. The following table lists the values:
If you then enter a value of 3 g for Total Polyunsaturated Fat, nutraCoster will update the Total Fat to be 13 g:
Entering Summary Values
nutraCoster does not change any of the detail values when you enter a total value.
In general, enter detail values first. nutraCoster will then automatically update the total values.