Linoleic acid

Encyclopedia of Alternative Medicine, Apr 06, 2001 by Melissa C. McDade

Linoleic acid is a colorless to straw-colored, liquid, polyunsaturated fatty acid (C18H32O2) of the omega-6 series. Linoleic and another fatty acid, gamma-linolenic, or gamolenic, produce prostaglandins. Prostaglandins are substances that are found in every cell, are needed for the body's overall health maintenance, and must be replenished constantly. Linoleic acid is an essential fatty acid, which means that the body cannot produce it, so it must be obtained in the diet.

Linoleic acid is an important fatty acid, especially for the growth and development of infants. Fatty acids help to maintain the health of cell membranes, improve nutrient use, and establish and control cellular metabolism. They also provide the raw materials that help in the control of blood pressure, blood clotting, inflammation, body temperature, and other body functions. Fatty acids are consumed in the greatest quantities in fat. Although many people are encouraged to consume less fat in their diets, fat is still an important component of a healthy body. Fat stores the body's extra calories, helps insulate the body, and protects body tissues. Fats are also an important energy source during exercise, when the body depends on its calories after using up available carbohydrates. Fat helps in the absorption, and transport through the bloodstream, of the fat-soluble vitamins A, D, E, and K.

Conjugated linoleic acid (CLA) is a naturally occurring mixture of various isomers of linoleic acid with conjugated double bonds. The isomers of CLA have different shapes, functions, and benefits. CLA supplements, or fats containing CLA, generally contain a mixture of these isomers. Although CLA is present in many foods and can be synthesized from linoleic acid, it is made naturally in the stomach, especially in ruminant animals. (Ruminants are animals that regurgitate food and chew it, known as "chewing the cud." Cows and sheep are ruminants.) For this reason, CLA is found primarily in dairy and beef products, as well as other foods derived from ruminant animals. Many people have likely decreased their intake of CLA for two reasons. First, beef and dairy fat are usually decreased or deleted from many diets. Second, many cattle are now fed grain diets, which are lower in linoleic acid than the grass on which they used to feed, so there is less CLA in beef and dairy foods. It is possible to increase the CLA in milk by adding a linoleic acid supplement to livestock feed. The supplement also increases lean tissue and decreases fat in the animals, and induces dairy cattle to produce more milk.

Linoleic acid is found in fish oil , meat, milk, and other dairy products. It is also a constituent of many vegetable oils, including evening primrose oil , sunflower oil, and safflower oil. Commercially produced linoleic acid is used in margarine, animal feeds, emulsifying agents, soaps, and drugs.

As mentioned, CLA supplements, or fats containing CLA, generally contain a mixture of CLA isomers. Plant oils, however, contain little CLA, but are a rich source of linoleic acid. While linoleic acid may be taken as a supplement to help with certain conditions, the supplement will not necessarily increase CLA levels in the body.

One particular isomer in CLA, known as cis-9, trans-11, is linked to anticancer benefits. Studies with animals have shown CLA to reduce breast, prostate, stomach, colorectal, lung, and skin cancers. The CLA may slow the growth of cells that give rise to cancer. A human study has shown an association between linoleic acids and a decreased risk for prostate cancer .

Infants with cystic fibrosis (CF) often have poor weight gain and growth and an inability to absorb fats. Some research suggests that infants with CF can benefit from formula with a high linoleic acid content because it optimizes nutrition, growth, and feeding efficiency.

Multiple sclerosis (MS) is a disease in which demyelination, loss of myelin sheath material, occurs. (The myelin sheath is a fatty substance that surrounds and insulates the axon of some nerve cells.) This leads to disruptions in nerve impulse transmission. Linoleic acid is believed to be helpful because myelin is composed of lecithin, which is made of linoleic and other fatty acids. Many diets recommended for MS patients include supplements. Patients supplementing with linoleic acid show a smaller increase in disability and reduced severity and duration of attacks than those with no linoleic acid supplement. Evening primrose oil is beneficial because of its specialized fatty-acid content, including linoleic acid. Doses of sunflower seed oil or evening primrose oil to provide 17 grams linoleic acid per day may be beneficial.

One study indicated that low doses of linoleic acid and calcium can reduce the incidence of preeclampsia in high-risk women. (Preeclampsia is the development of hypertension with increased protein in the urine or accumulation of watery fluid in cells or tissues or both, due to pregnancy.) Another study showed, however, that linoleic acid consumption can have a negative effect on fetal growth. Pregnant women should talk to their doctors before taking linoleic acid or any other supplement.