Balancing Fatty Acids
April 2000 -- Nutrition Notes

By: Andrea Platzman, R.D.
Contributing Editor

  Most fats have a bad reputation, but not all deserve it. We're learning that specific fatty acids have specific physiological effects. Stearic acid, for example, although saturated, is thought to be neutral with regard to raising cholesterol levels. For optimum health, it's imperative to not only consume the right fatty acids, but to do so in the right balance.

Bond, double bond

  Molecularly speaking, fats are triglycerides - or more specifically, triacylglycerols - consisting of three fatty acids attached to a glycerol backbone. The fatty acids vary in carbon-chain length, positions and configuration of double bonds and degree of saturation.

  Fatty acids with no double bonds - i.e., as many hydrogen atoms as possible attached to the carbons - are saturated fats. Animal fats and certain vegetable oils, especially palm, coconut and palm kernel, are classified as saturated fats.

  Fatty acids with one double bond, prevalent in canola, peanut and olive oils, are monounsaturated. Fatty acids with more than one double bond, which occur in high levels in marine oils and corn, sunflower, soybean and other vegetable oils, are polyunsaturated. Hydrogenation increases saturation. Although fats almost always contain a mixture of fatty acids, we often label them as saturated or unsaturated based on the ratio of fatty acids present.

  Because changing even a single atom in a molecule can profoundly affect its chemical properties, saturated and unsaturated fats have different effects on health. Saturated fats have been associated with raised levels of blood cholesterol, which can eventually restrict blood flow, especially to the heart. A diet high in saturated fats is also linked to obesity and certain cancers. Monounsaturates and polyunsaturates, however - particularly when substituted for saturates - can actually reduce blood-cholesterol levels, in part by spurring the liver to clear cholesterol from the blood.

Omega unsaturates

  Omega-6 and omega-3 fatty acids are two of the most well-researched polyunsaturates. Linoleic acid, with 18 carbons and two double bonds, is an essential omega-6 fatty acid; the omega-6 designation refers to the number of carbons between the final double bond and the fat's terminal methyl group. The body cannot manufacture linoleic acid; it must be ingested. Given linoleic acid, the body can synthesize linoleic acid's 20-carbon relative, arachidonic acid (AA), which is one of the omega-6 PUFAs that are essential components of the phospholipids in cell membranes. The primary dietary sources of omega-6 PUFAs are vegetable oils and meats.

  Linolenic acid, with 18 carbons and three double bonds, is an essential omega-3 PUFA. Given dietary linolenic acid, the body can synthesize eicosapentaenoic acid (EPA), a 20-carbon omega-3 fatty acid and docosahexaenoic acid (DHA), a 22-carbon omega-3 fatty acid. To effectively increase body stores of EPA and DHA, consuming fatty fish, soybeans and flaxseed oil is recommended.  Both linoleic and linolenic fatty acids are important to health, especially cardiovascular health. Linoleic's greatest area of impact is LDL/HDL ratio regulation, whereas linolenic protects against blood clotting and stabilizes the heart against abnormal beating.

  Omega-3 fatty acids help protect the heart against cardiovascular disease by inhibiting the formation of blood clots, lowering triglyceride levels and stopping the plaque growth that narrows arteries leading to the heart. A growing body of research suggests that omega-3s also affect brain function later in life. Preliminary studies have linked a deficit of DHA with dyslexia, attention-deficit disorder and depression. Omega-3 fatty acids also protect against and help treat many other ailments.

  In a study published in the March 2000 issue of Developmental Medicine and Child Neurology, it was reported that infant's whose formula was enriched with DHA and AA exhibited a somewhat increased intellectual capacity as compared to a control group receiving commercial formula. The theory is that by adding these essential fatty acids, the formula more closely resembles mother's milk in its effect on infant brain development. The children in the study will be tested again when older to help determine the subsequent effects, if any, of their enhanced early brain development. While many countries have already approved adding DHA and AA to infant formula, the FDA is weighing the evidence carefully and considering potential long-term effects before issuing any new regulations.

Fatty acid balance

  The American Heart Association recommends maintaining a fatty-acid balance of 1:1:1 saturated:polyunsaturated:monounsaturated fatty acids. Although studies are still being conducted to better define the best fatty-acid balance for optimal health, it is known that the ratio of omega-6s to omega-3s in the body is crucial. While the ideal ratio is believed to be 5:1, the ratio in the typical Western diet has shifted to between 10:1 to 40:1. Such a skewed ratio could have life-threatening consequences, such as cardiac arrhythmias and increased blood clotting, and may also promote inflammatory diseases such as rheumatoid arthritis and asthma.

  The omega imbalance is probably due to an excessive intake of commercial vegetable oils and a limited intake of fish. Beginning in the 1960s, Americans were advised to replace foods high in saturated fats and cholesterol with polyunsaturated fats. At the same time, many more processed foods - usually low in omega-3 polyunsaturated fatty acids - were being consumed.

  The British Nutrition Foundation, Health Canada, and the World Health Organization recommend that 1% of dietary fat intake come from omega-3s. There are currently no official United States dietary guidelines for omega-3s, although many experts consider 3 grams daily a reasonable level. As further research is carried out, new information on fatty acids and their effects is sure to follow.

Andrea D. Platzman, a registered dietitian, writes regularly for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.

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