Lecithin
Lecithin
Dietary and commercial sources
Lecithin is a phospholipid, a yellow-brown fatty substance that consists of glycerol, two fatty acids, a phosphate group, and choline.
Lecithin was first found in eggs in 1846, so its name was coined from the Greek word for egg yolk, lekithos. Though lecithin is its common name, chemists refer to it as phosphatidylcholine. In contrast to fats, which function as fuel molecules, lecithin serves a structural role in cell membranes. It is found in all cells.
Without lecithin and other membrane phospholipids, cells would be unable to maintain their structure and probably would dissolve back into their surroundings. Lecithin is apparently vital for life in mammals, because no hereditary diseases in its biosynthesis are known. (A genetic defect involving a vital substance is lethal to the organism and therefore cannot be passed on.)
The lecithin available in stores is actually a mixture of lecithin and other phospholipids as well as fatty (soybean) oil. Its fatty acid components can vary, depending on the number of carbonatoms they contain and whether they are saturated or unsaturated. The nature of the fatty acid components in a lecithin molecule greatly influence its role. For example, a lecithin molecule in which both fatty acids are saturated aids oxygen uptake in the lungs. Another “species” of lecithin, which contains two unsaturated fatty acids is involved in the transport of cholesterol in the blood.
Structure and properties
The structure of lecithin is illustrated in Figure 1. Glycerol, which contains three carbon atoms, serves as the backbone of the lecithin molecule. The two fatty acids are linked to glycerol at carbon atoms 1 and 2 and the phosphate group is linked to carbon atom 3. Choline is, in turn, linked to the phosphate group. Typically, though not always, the fatty acid attached to carbon 1 of glycerol is saturated, while that attached to carbon 2 is unsaturated.
To get a simple idea of the structure of the lecithin molecule, imagine a balloon with two long paper streamers attached to it. The balloon or “head” region corresponds to the polar portion of the molecule, the negatively charged phosphate group, and the positively charged choline, which readily dissolve in water. The streamers or “tails” represent the nonpolar part, the long chain of 12 to 18 carbon atoms in the
two fatty acids, which are insoluble in water. As a result of the nature of its head and tail groups, lecithin molecules tend to disperse themselves in water with their nonpolar tails back-to-back to form bilayers, or double layers, in which the polar heads project outward into the water. This arrangement sequesters, or conceals, the nonpolar tails away from the water, forming a structural barrier to the passage of polar and ionic molecules as shown.
Dietary and commercial sources
Because lecithin is found in all living organisms, it is readily available in foods. Egg yolks, liver, peanuts, corn, spinach, and whole grains are good dietary sources. Soybeans are by far the most important commercial source of lecithin, because they are an excellent source, and because such huge amounts are produced. Commercial lecithin is widely used to process food products, including baking mixes, candy, chewing gum, chocolate, ice cream, macaroni and noodles, margarine, whipped toppings, and so on. It is used as an emulsifier—a substance that can blend water and oil. However, the amounts used as a food additive in such products are not enough to be a good dietary source of lecithin.
Role in health and disease
Lecithin is the most abundant membrane phospholipid in our cells. A study involving cells with a temperature-sensitive genetic defect in lecithin biosynthesis illustrates how essential it is for cell survival. When grown above a certain temperature, these cells were unable to make lecithin. Under these conditions the cells began to burst open and eventually died.
Several studies suggest that lecithin is involved in cell signaling, the process by which one cell initiates changes in another. For example, a hormone, neuro-transmitter, or growth factor secreted by one cell communicates with another by altering its cell membrane in some way, usually by activating an enzyme that breaks down phospholipid in the membrane. The breakdown products interact with an enzyme that sets into motion a domino effect of changes in cell growth, metabolism, function, and so on. Disruptions in this process may give rise to certain diseases. Some recent evidence suggests that lecithin deficiency may interfere with cell signaling and so may be a factor in the development of liver and colon cancer.
Lecithin plays an important role in the transport of fats and cholesterol from the liver to sites where they can be either used or stored. Since fats do not dissolve in water solutions like blood plasma, they are transported in spherical particles called lipoproteins. These particles can mix with water solutions because the water-friendly proteins, cholesterol, and phospholipids are on the outside surface. The nonpolar fats associated with them make up the core, which is unex-posed to water. Because lecithin is required for lipoprotein synthesis, a lecithin deficiency results in fats accumulating in the liver and leads to liver damage. Lecithin deficiency also leads to increased amounts of cholesterol in the blood and atherosclerosis, a disease in which narrowing of the arteries is caused primarily by the deposit of fats from the bloodstream.
Lecithin is the primary source of choline, the precursor of the neurotransmitter acetylcholine. Recent findings suggest a relationship between the lack of availability of lecithin to nerve cells that produce acetylcholine, and the progress of Alzheimer’s disease.
Commercial importance
Commercial lecithin is actually a mixture of lecithin, other related phospholipids, and oil. Due to its ability to break up fat and oil globules and its antioxidant properties, lecithin extracted from soybeans is important commercially for processing food and other products. In food it aids in the mixing of vegetable oils, butters, and other fatty ingredients so that they are distributed uniformly. Without lecithin these ingredients tend to separate. A familiar example is the separation of cocoa butter out of chocolate, leaving a
KEY TERMS
Lipid —Any fatty substance that tends not to dissolve in water but instead dissolves in relatively nonpolar organic solvents.
Phospholipid —A lipid that contains a phosphate group.
Saturated —Containing a single bond between the carbon atoms in a chain.
Unsaturated —Containing multiple bonds between the carbon atoms in a chain. Unsaturated fatty acids contain at least one double bond between two carbon atoms.
light oily film on the surface. Lecithin stabilizes oils against oxidation during processing, producing better flavor and longer shelf life. Lecithin is also used in the manufacture of paints, dyes, inks, leather goods, plastics, cosmetics, textiles, and pharmaceutical products, among others.
Resources
PERIODICALS
Bretscher, Mark S. “The Molecules of the Cell Membrane.”
Scientific American. (October 1985): 100-08.
Canty, David J., and Steven H. Zeisel. “Lecithin and
Choline in Human Health and Disease.” Nutrition Reviews, 52, (1994): 327.
Delaney, Lisa, and Cemela London. “Dictionary of Healing
Techniques and Remedies-part 35.” Prevention, 44, (February 1992): 135.
OTHER
PDR Health. “Phosphatidylcholine” <http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/pho_0288.shtml> (accessed December 2, 2006).
United Soybean Board: Talk Soy. “Soy Lecithin Fact Sheet” <http://www.talksoy.com/pdfs/SoyLecithinFactSheet3.pdf> (accessed December 2, 2006).
Patricia V. Racenis
Lecithin
Lecithin
Lecithin is a phospholipid which consists of glycerol , two fatty acids , a phosphate group and choline.
Lecithin was first found in eggs in 1846, so its name was coined from the Greek word for egg yolk, lekithos. Though lecithin is its common name, chemists refer to it as phosphatidylcholine. It is a yellow-brown fatty substance. In contrast to fats, which function as fuel molecules, lecithin serves a structural role in cell membranes. It is found in all cells. Without lecithin and other membrane phospholipids, cells would be unable to maintain their structure and probably would dissolve back into their surroundings. Lecithin is apparently vital for life in mammals , because no hereditary diseases in its biosynthesis are known. (A genetic defect involving a vital substance is lethal to the organism and therefore cannot be passed on.) The lecithin we purchase in a store is actually a mixture of lecithin and other phospholipids as well as fatty (soy bean) oil. The fatty acid components in lecithin can vary, depending on the number of carbon atoms they contain and whether they are saturated or unsaturated. The nature of the fatty acid components in a lecithin molecule greatly influence its role. For example, a lecithin molecule in which both fatty acids are saturated aids oxygen uptake in the lungs. Another "species" of lecithin, which contains two unsaturated fatty acids is involved in the transport of cholesterol in the blood .
Structure and properties
The structure of lecithin is illustrated here. Glycerol, which contains three carbon atoms, serves as the backbone of the lecithin molecule. The two fatty acids are linked to glycerol at carbon atoms 1 and 2 and the phosphate group is linked to carbon atom 3. Choline is, in turn, linked to the phosphate group. Typically, though not always, the fatty acid attached to carbon 1 of glycerol is saturated, while that attached to carbon 2 is unsaturated.
To get a crude idea of the structure of the lecithin molecule, imagine a balloon with two long paper streamers attached to it. The balloon or "head" region corresponds to the polar portion of the molecule, the negatively-charged phosphate group, and the positivelycharged choline, which readily dissolve in water . The streamers or "tails" represent the nonpolar part, the long chain of 12 to 18 carbon atoms in the two fatty acids, which are insoluble in water. As a result of the nature of its head and tail groups, lecithin molecules tend to disperse themselves in water with their nonpolar tails back-to-back to form bilayers, or double layers, in which the polar heads project outward into the water. This arrangement sequesters, or conceals, the nonpolar tails away from the water, forming a structural barrier to the passage of polar and ionic molecules as shown.
Dietary and commercial sources
Because lecithin is found in all living organisms, it is readily available in foods. Egg yolks, liver, peanuts, corn, spinach , and whole grains are good dietary sources. Soy beans are by far the most important commercial source of lecithin, because they are an excellent source, and because such huge amounts are produced. Commercial lecithin is widely used to process food products, including baking mixes, candy, chewing gum, chocolate, ice cream, macaroni and noodles, margarine, whipped toppings, and so on. It is generally used as an emulsifier, a substance that can bring water and oil together. However, the amounts used as a food additive in such products are not enough to be a good dietary source of lecithin.
Role in health and disease
Lecithin is the most abundant membrane phospho-lipid in our cells. A study involving cells with a temperature-sensitive genetic defect in lecithin biosynthesis illustrates how essential it is for cell survival. When grown above a certain temperature , these cells were unable to make lecithin. Under these conditions the cells began to burst open and eventually died.
Several studies suggest that lecithin is involved in cell signaling, the process by which one cell initiates changes in another. For example, a hormone, neuro-transmitter , or growth factor secreted by one cell communicates with another by altering its cell membrane in some way, usually by activating an enzyme which breaks down phospholipid in the membrane. The breakdown products interact with an enzyme which sets into motion a domino effect of changes in cell growth, metabolism , function, and so on. Disruptions in this process may give rise to certain diseases. Some recent evidence suggests that lecithin deficiency may interfere with cell signaling and so may be a factor in the development of liver and colon cancer .
Lecithin plays an important role in the transport of fats and cholesterol from the liver to sites where they can be either used or stored. Since fats do not dissolve in water solutions like blood plasma , they are transported in spherical particles called lipoproteins. These particles can mix with water solutions because the water-friendly proteins , cholesterol and phospholipids are on the outside surface. The nonpolar fats associated with them make up the core, which is unexposed to water. Because lecithin is required for lipoprotein synthesis, a lecithin deficiency results in fats accumulating in the liver and leads to liver damage. Lecithin deficiency also leads to increased amounts of cholesterol in the blood and atherosclerosis, a disease in which narrowing of the arteries is caused primarily by the deposit of fats from the bloodstream.
Lecithin is the primary source of choline, the precursor of the neurotransmitter acetylcholine . Recent findings suggest a relationship between the lack of availability of lecithin to nerve cells which produce acetylcholine, and the progress of Alzheimer disease .
Commercial importance
Commercial lecithin is actually a mixture of lecithin, other related phospholipids and oil. Due to its ability to break up fat and oil globules and its antioxidant properties, lecithin extracted from soy beans is important commercially for processing food and other products. In food it aids in the mixing of vegetable oils, butters, and other fatty ingredients so that they are uniformly distributed throughout the product. Without lecithin these ingredients tend to separate out. A familiar example is the separation of fat out of chocolate, leaving a light oily film on the surface. Lecithin stabilizes oils against oxidation during processing, resulting in better flavor and longer shelf life. Lecithin is also used in the manufacture of paints, dyes, inks, leather goods, plastics , cosmetics, textiles , and pharmaceutical products, among others.
Resources
periodicals
Bretscher, Mark S. "The Molecules of the Cell Membrane." Scientific American (October 1985): 100-08.
Canty, David J., and Steven H. Zeisel. "Lecithin and Choline in Human Health and Disease." Nutrition Reviews, 52, (1994): 327.
Delaney, Lisa, and Cemela London. "Dictionary of Healing Techniques and Remedies-part 35." Prevention, 44, (February 1992): 135.
Patricia V. Racenis
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Lipid
—Any fatty substance which tends not to dissolve in water but instead dissolves in relatively nonpolar organic solvents.
- Phospholipid
—A lipid which contains a phosphate group.
- Saturated
—Containing a single bond between the carbon atoms in a chain.
- Unsaturated
—Containing multiple bonds between the carbon atoms in a chain. Unsaturated fatty acids contain at least one double bond between two carbon atoms.
Lecithin
Lecithin
Definition
Lecithin was discovered in 1850 by Maurice Gobley, who isolated it in egg yolks and identified it as the substance that allowed oil and water to mix. The name is derived from the Greek word lekithos, which means "yolk of egg." Lecithin is a naturally occurring fatty substance found in several foods including soybeans, whole grains and egg yolks. It is often used as an emulsification agent in processed foods. It can be taken in various forms as a nutritional supplement, often derived from soybeans. The body breaks lecithin down into its component parts: choline, phosphate, glycerol and fatty acids. The body's highest concentration of lecithin is found in the vital organs, where it makes up about 30% of the dry weight of the brain and nearly two-thirds of the fat in the liver.
General use
Lecithin acts as an emulsifier and helps the body in the absorption of fats. A 1999 study indicates that soy lecithin improves the metabolism of cholesterol in the digestive system. Therefore, lecithin has been touted as a treatment for high cholesterol. It has also been said to be a treatment for neurologic and liver disorders. Promoters claim that supplemental lecithin can be used to help lower cholesterol and deter memory loss . Some proponents of lecithin warn that the low fat and low cholesterol diets that many Americans follow may lower the amount of lecithin that we consume, creating a deficit and necessitating supplemental lecithin. As Americans eat fewer eggs, meats, and dairy products, the amount of choline that they consume may be less than required. Choline is the key element in lecithin that researchers believe may have a beneficial effect on cholesterol and memory.
Lecithin has been identified as a possible resource for lowering blood cholesterol because of its reputation as a source of polyunsaturated fats. In addition, choline helps the liver metabolize fat and form lipoproteins. However, there is still scanty evidence to support the use of lecithin in lowering cholesterol. Researchers in some studies have found a drop in cholesterol levels, while others have found no drop in cholesterol levels at all. A group of researchers from the Netherlands summarized findings in the American Journal of Clinical Nutrition that found that many studies of the effects of lecithin had faulty methods, and the few good studies proved that lecithin was not effective in lowering cholesterol. More recently, a group of American researchers solved part of the mystery concerning the fact that eggs, which are packed with cholesterol, don't impact people's cholesterol much if eaten in moderation. The reason seems to be the lecithin found in eggs that reduces cholesterol's absorption in the bloodstream.
Lecithin is also considered to be of possible benefit to brain function, and supporters claim that it may help prevent Alzheimer's disease. Promoters indicate that the choline in lecithin may have the ability to penetrate the blood-brain barrier and impact the production of acetylcholine, a neurotransmitter that facilitates brain function. They claim that long-term use of lecithin as a dietary supplement could help minimize memory loss. However, studies on the use of lecithin for the treatment of Alzheimer's disease have found that it has no marked benefit.
Preparations
Lecithin is derived from soy and is available in capsule, liquid and granule form. Consumers should not use a synthetic form of the supplement (choline chloride), but should seek one that contains natural phosphatidyl choline. Lecithin from soybeans generally contains about 76% phosphatidycholine. Studies of supplements sold in health food stores show that most contain minimal levels of pure lecithin. In fact, a person might get the same benefit from eating a handful of peanuts. The American Heart Association and the College of Physicians and Surgeons of Columbia University described lecithin supplements as "an expensive way of adding unsaturated fatty acids to the diet."
Precautions
Consumers should be aware that most nutritional supplements are not regulated by the Food and Drug Administration (FDA) for product safety or effectiveness. Because lecithin is not considered an essential nutrient, currently, no Recommended Daily Allowance (RDA) has been set for this nutrient.
Side effects
There are no major side effects for lecithin as a supplement. In high doses (more than 25 g per day), lecithin can cause sweating, upset stomach, diarrhea, nausea and vomiting . Pregnant or nursing women and children should avoid the supplement because it has not been adequately tested for safety.
Resources
PERIODICALS
Buchanan, Caroline. "Lecithin Supplements: A Source of Help or Hype?" Environmental Nutrition (June, 1989):1-3.
Gormley, James J. "Brewer's Yeast and Lecithin-Two Underrated Health Promoters." Better Nutrition (February, 1997): 32-33.
LaBell, Fran. "Lecithin: A Source for Vital Choline." Prepared Foods (September, 1997): 79-80.
"Lecithin." Vegetarian Times (February 2000): 24.
Rafinski, Karen. "Alternatives" The Record (Bergen County, NJ), (April 10, 2000): H5.
"Shell Shocker. (Nutrition Bulletin)." Men's Health (April 2002): 32.
Zupke, Mary Payne and Ira Milner. "Bee Pollen, Shark Cartilage, Ginseng: The Truth about 10 Top Supplements." Environmental Nutrition (September 1993): 1-4.
OTHER
"Soy Lecithin." Alternative Herbal Index. http://www.OnHealth.com/alternative/resource/herbs/item,77184.asp. (June 14, 2000).
Amy Cooper
Teresa G. Odle
lecithin
lecithin
lecithin
lec·i·thin / ˈlesə[unvoicedth]in/ • n. Biochem. a substance widely distributed in animal tissues, egg yolk, and some higher plants, consisting of phospholipids linked to choline.