Omega-3 Fatty Acids: Metabolism Matters

June 3, 2008

7 Min Read
Omega-3 Fatty Acids:  Metabolism Matters

Omega-3 fatty acids are definitely on consumers’ radar. In the 2007 “Food & Health” survey from the International Food Information Council, Washington D.C., 71% of consumers reported they were aware of omega-3 fatty acids, up from 63% in 2006. But the omega-3 fatty acids’ effect on health is far more complicated than meets the eye.

“The metabolism of omega-3 fatty acids is underappreciated,” says Joyce Nettleton, D.Sc., editor, “Fats of Life” newsletter and “PUFA Newsletter.” Indeed, consumers may have a hard time grappling with the complexities of omega-3 fatty acids actions and the differences between individual omega-3 fatty acids, especially when combined with the many overlapping concerns that muddy the waters, including fat vilification, fish toxicity, endangered fish species and vegetarianism.

Omega-3s up close

“It is very important to look at what type of omega-3s people are getting,” says Nettleton. After all, not all omega-3s are created equally, structurally and functionally. Classified as polyunsaturated fatty acids (PUFAs), all omega-3 fatty acids have their first double bond located between the third and fourth carbon atom, counting from the methyl end of the fatty acid (n-3). Omega-6 fatty acids’ first double bond is positioned between the sixth and seventh carbon atom from the methyl end of the fatty acid (n-6). Because humans lack the enzyme required to insert a cis double bond at the n-6 or n-3 position of a fatty acid, consuming omega-3 and omega-6 fatty acids is essential.

The 18-carbon omega-3 fatty acid, alpha-linolenic acid (ALA), is a parent fatty acid within the omega-3 fatty acid group—humans can synthesize important long-chain (at least 20 carbons) omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from it. The conversion of ALA, commonly found in plant sources like flax seed, soy, walnuts and canola oil, to the important long-chain omega-3 fatty acids, EPA and DHA, is modest.

The long-chain gang

A growing body of evidence is linking increased EPA and DHA intakes to decreased risk of cardiovascular disease, arrhythmias that can lead to sudden cardiac death, and thrombosis that can prompt myocardial infarction or stroke, as well as decreased levels of triglycerides, slower growth of atherosclerotic plaque, improved vascular endothelial function, modest blood pressure lowering, and decreased inflammation. FDA has concluded there is sufficient evidence for a qualified health claim for omega-3 fatty acids, EPA and DHA, and the risk of coronary heart disease. In addition, long-chain omega-3 fatty acids have shown success in treating symptoms of rheumatoid arthritis and psychiatric disorders, including schizophrenia and major depressive disorder.

DHA, in particular, might play an important role in vision and central nervous function, since it is part of retinal cell and postsynaptic neuronal cell membranes. Brain gray matter phospholipids contain high levels of DHA. Especially critical is the knowledge that DHA is accumulated in the fetal brain and retina during the last trimester of pregnancy. “Because it is crucial for fetal brain development and function, it is recommended that pregnant and nursing women consume at least 200 mg per day of DHA,” says Nettleton. “There is growing evidence that this long-chain omega-3 is essential throughout most of life. Later in life, this fatty acid may reduce the risk of Alzheimer’s disease. It also helps protect neurons.”

EPA has its own important functions related to anti-inflammatory and anti-thrombotic actions. During an inflammatory response, the omega-6 fatty acid, arachidonic acid (AA), and EPA in cell membranes can be metabolized by enzymes to form prostaglandins and leukotrienes. If more AA than EPA is found in the diet, as is typical in the United States, the formation of more eicosanoids derived from AA occurs rather than those derived from EPA. The body responds to these eicosanoids differently. “Eicosanoids derived from AA tend to promote platelet aggregation and thrombosis, which doesn’t help the heart. Eicosanoids derived from EPA dampen down these pro-inflammatory effects, because they compete for the same enzymes and yield products with only weak inflammatory effects,” says Nettleton.

Resolvins derived from EPA may have specific benefits, as well. “Resolvins appear to signal the end of inflammatory processes, acting like a traffic cop with a stop sign,” says Nettleton. “All of these things are connected. It sometimes seems hard to believe that a group of compounds and their derivatives have so many effects in the body.”

The ALA conundrum

But what about omega-3 in plant foods (ALA)? “It’s not that the plant sources are bad for you, but they are not providing the same level of long-chain omega-3 fatty acids provided by eating fish. The body needs DHA, and almost no ALA is converted into DHA. There may be some conversion, but it occurs at very low levels, below 1%,” says Nettleton. The pathways for conversion of ALA to long-chain fatty acids compete for the same enzymes as the omega-6 fatty acid, linoleic acid (LA). Unlike long-chain omega-3s, LA is plentiful in the Western diet.

That’s not to say that including more omega-3s from plant sources is a bad idea. Many studies have suggested that higher dietary intakes of ALA are linked with significant lowering of coronary heart disease risk. Omega-3s in plants like soy, flax and canola will give some heart-health and immune-function benefits, but due to the low conversion rates they aren’t “as potent as those from the long-chain omega-3 fatty acids,” says Nettleton. “The conversion of ALA to EPA and DHA is still not well understood. But if people increase the amount of ALA without increasing LA, they should experience a higher amount of total conversion to EPA and DHA,” reports Nam Fong Han, Ph.D., president/CEO of Natunola Health Inc., a manufacturer of flaxseed ingredients in based in Ottawa, Ontario.

The omega-3 fix

Long-chain omega-3s are primarily found in seafood, including salmon, tuna, sardines, mackerel and shellfish. Omega-3-enriched eggs, as well as supplements made of fish-oil, algal or fungal sources, are also good sources of DHA. Supplemental forms of long-chain omega-3 fatty acids usually have lower levels of methylmercury, PCBs and dioxins compared to eating fish.

The Institute of Medicine’s Dietary Reference Intake bases recommendations for adequate intake (AI) of omega-3 fatty acids on ALA intake, recognizing that dietary DHA and EPA can meet some of this amount. The AI for ALA is 1.1 to 1.6 grams per day for women and men, respectively. The average adult intake of EPA and DHA is 0.04 to 0.07 grams per day and 0.05 to 0.09 grams per day, respectively. Doses of EPA and DHA used in major studies were 2.0 to 3.0 grams per day of EPA, and about 1.0 to 2.5 grams per day of DHA.

Some evidence links the imbalance of omega-6 fatty acid intake vs. omega-3 fatty acid intake as a possible root for the development of chronic diseases such as heart disease, cancer, asthma, arthritis and depression. Optimally, people should consume somewhere between a ratio of 1:1 to 4:1 omega-6 to omega-3 fatty acids, but today, Americans consume about 11 to 30 times more omega-6 than omega 3-fatty acids. “We exhibit high rates of chronic diseases associated with low consumption of omega-3s, such as cardiovascular and immune-related conditions. The United States has one of the lowest intakes of long-chain omega-3 fatty acids in the world,” stresses Nettleton.

It’s clear that there will be much attention on the long-chain forms of omega-3 fatty acids in the future.

Sharon Palmer is a registered dietitian with 16 years of experience in health-care and foodservice management. She writes on food and nutrition for newspapers, magazines, websites and books. Palmer makes her home in Southern California and can be reached at [email protected].

Shooting Stars

Omega-3s have risen to functional superstar status. The market for omega-3-fortified foods, from beverages and cereals to spreads and bakery products, has expanded from $100 million in 2002 to $2 billion in 2006, according to “Omega 3 Fatty Acids and the U.S. Food and Beverage Market,” a new study from Packaged Facts, Rockville, MD.

Drinking Up Omega-3 Juice Opportunities

According to Zenith International Ltd., Bath, England, global sales of omega-3 beverages were estimated at €5.8 billion in 2006, and it projects a 34% increase through 2011 as these beverages continue to go mainstream. The company’s “Omega-3 Drinks Report 2008” also identifies opportunities in this market:

■ The overall market is supported by a strong juice tradition, especially enriched juice, in the United States;

■ Additionally, omega-3 has increasing penetration of a solid dairy market in Asia and Australasia;

■ The abundance of scientific research showing omega-3 is an essential health component with benefits at every life stage signals increased expansion;

■ The main markets for omega-3 beverage fortification are the more established markets of North America and Western Europe, where the concept has been around for five to ten years;

■ North America and Western Europe experienced the highest growth in 2006, and the strong growth should continue through to 2011.

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