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Omega-3 fatty acid

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Types of Fats in Food
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Omega-3 fatty acids are a family of polyunsaturated fatty acids which have in common a carbon-carbon double bond in the ω-3 position. (See Nomenclature for terms and discussion of ω (omega) nomenclature.)

Important omega-3 fatty acids in nutrition are: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). For a more complete list see List of omega-3 fatty acids. The human body cannot synthesize omega-3 fatty acids de novo, but can synthesize all the other necessary omega-3 fatty acids from the simpler omega-3 fatty acid α-linolenic acid. Therefore, α-linolenic acid is an essential nutrient which must be obtained from food, and the other omega-3 fatty acids which can be either synthesized from it within the body or obtained from food are sometimes also referred to as essential nutrients.



[edit] Chemistry

For detail on omega (ω) nomenclature and numbering, see EFA Nomenclature.
Chemical structure of alpha-linolenic acid (ALA), an essential omega-3 fatty acid, (18:3Δ9c,12c,15c). Although chemists count from the carbonyl carbon (blue numbering), physiologists count from the omega (ω) carbon (red numbering). Note that from the omega end (diagram right), the first double bond appears as the third carbon-carbon bond (line segment), hence the name "omega-3"
Chemical structure of alpha-linolenic acid (ALA), an essential omega-3 fatty acid, (18:3Δ9c,12c,15c). Although chemists count from the carbonyl carbon (blue numbering), physiologists count from the omega (ω) carbon (red numbering). Note that from the omega end (diagram right), the first double bond appears as the third carbon-carbon bond (line segment), hence the name "omega-3"

The term omega-3 (aka "n-3", "ω-3") signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (ω) of the carbon chain.

Omega-3 fatty acids which are important in human nutrition are: α-linolenic acid (18:3, ALA), eicosapentaenoic acid (20:5, EPA), and docosahexaenoic acid (22:6, DHA). These three polyunsaturates have either 3, 5 or 6 double bonds in a carbon chain of 18, 20 or 22 carbon atoms, respectively. All double bonds are in the cis-configuration, i.e. the two hydrogen atoms are on the same side of the double bond.

[edit] Biological significances

The biological effects of the ω-3 fatty acids are largely mediated by their interactions with the ω-6 fatty acids; see Essential fatty acid interactions for detail.

A 1992 article by biochemist William E.M. Lands[1] provides an overview of the research into omega-3 fatty acids, and is the basis of this section.

The 'essential' fatty acids were given their name when researchers found that they were essential to normal growth in young children and animals. (Note that the modern definition of 'essential' is more strict.) A small amount of omega-3 in the diet (~1% of total calories) enabled normal growth, and increasing the amount had little to no additional benefit.

Likewise, researchers found that omega-6 fatty acids (such as γ-linolenic acid and arachidonic acid) play a similar role in normal growth. However, they also found that omega-6 was "better" at supporting dermal integrity, renal function, and parturition. These preliminary findings led researchers to concentrate their studies on omega-6, and it was only in recent decades that omega-3 has become of interest.

In 1963 it was discovered that the omega-6 arachidonic acid was converted by the body into pro-inflammatory agents called prostaglandins. By 1979 more of what are now known as eicosanoids were discovered: thromboxanes, prostacyclins and the leukotrienes. The eicosanoids, which have important biological functions, typically have a short active lifetime in the body, starting with synthesis from fatty acids and ending with metabolism by enzymes. However, if the rate of synthesis exceeds the rate of metabolism, the excess eicosanoids may have deleterious effects. Researchers found that omega-3 is also converted into eicosanoids, but at a much slower rate. Eicosanoids made from omega-3 fats often have opposing functions to those made from omega-6 fats (ie, anti-inflammatory rather than inflammatory). If both omega-3 and omega-6 are present, they will "compete" to be transformed, so the ratio of omega-3:omega-6 directly affects the type of eicosanoids that are produced.

This competition was recognized as important when it was found that thromboxane is a factor in the clumping of platelets, which leads to thrombosis. The leukotrienes were similarly found to be important in immune/inflammatory-system response, and therefore relevant to arthritis, lupus, and asthma. These discoveries led to greater interest in finding ways to control the synthesis of omega-6 eicosanoids. The simplest way would be by consuming more omega-3 and fewer omega-6 fatty acids.

[edit] Health benefits

On September 8, 2006, the U.S. Food and Drug Administration gave "qualified health claim" status to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) omega-3 fatty acids, stating that "supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease."[2] This updated and modified their health risk advice letter of 2001 (see below).

A 2006 report in the Journal of the American Medical Association concluded that their review of literature covering cohorts from many countries with a wide variety of demographic characteristics failed to demonstrate a link between omega-3 fatty acids and cancer prevention.[3] This is similar to the findings of a review by the British Medical Journal of studies up to February 2002 that failed to find clear effects of long and shorter chain omega-3 fats on total mortality, combined cardiovascular events and cancer.[4]

In April 2006, a team led by Lee Hooper at the University of East Anglia in Norwich, UK, published a review of almost 100 separate studies into omega-3 fatty acids, found in abundance in oily fish. It concluded that they do not have a significant protective effect against cardiovascular disease.[5] This meta-analysis was controversial and stands in stark contrast with two different reviews also performed in 2006 by the American Journal of Clinical Nutrition[6] and a second JAMA review[7] that both indicated decreases in total mortality and cardiovascular incidents (i.e. myocardial infarctions) associated with the regular consumption of fish and fish oil supplements.

Several studies published in 2007 have been more positive. In the March 2007 edition of the journal Atherosclerosis, 81 Japanese men with unhealthy blood sugar levels were randomly assigned to receive 1800 mg daily of eicosapentaenoic acid (EPA - an omega-3 essential fatty acid from fish oil) with the other half being a control group. The thickness of the carotid arteries and certain measures of blood flow were measured before and after supplementation. This went on for approximately two years. A total of 60 patients (30 in the EPA group and 30 in the control group) completed the study. Those given the EPA had a statistically significant decrease in the thickness of the carotid arteries along with improvement in blood flow. The authors indicated that this was the first demonstration that administration of purified EPA improves the thickness of carotid arteries along with improving blood flow in patients with unhealthy blood sugar levels.

In another study published in the American Journal of Health System Pharmacy March 2007, patients with high triglycerides and poor coronary artery health were given 4 grams a day of a combination of EPA and DHA along with some monounsaturated fatty acids. Those patients with very unhealthy triglyceride levels (above 500 mg/dl) reduced their triglycerides on average 45% and their VLDL cholesterol by more than 50%. VLDL is a bad type of cholesterol and elevated triglycerides can also be deleterious for cardiovascular health.

There was another study published on the benefits of EPA in the prestigious journal The Lancet in March 2007. This study involved over 18,000 patients with unhealthy cholesterol levels. The patients were randomly assigned to receive either 1,800 mg a day of EPA with a statin drug or a statin drug alone. The trial went on for a total of five years. It was found at the end of the study those patients in the EPA group had superior cardiovascular function. Non-fatal coronary events were also significantly reduced in the EPA group. The authors concluded that EPA is a promising supplement for promoting cardiovascular health.

Another study regarding fish oil was published in the journal Nutrition in April 2007. Sixty four healthy Danish infants received either cow's milk or infant formula alone or with fish oil from nine to twelve months of age. It was found that those infants supplemented with fish oil had improvement in immune function maturation with no apparent reduction in immune activation.

There was yet another study on omega-3 fatty acids just published in the April 2007 Journal of NeuroScience. A group of mice were genetically modified to develop accumulation of amyloid and tau proteins in the brain similar to that seen in people with poor memory. The mice were divided into four groups with one group receiving a typical American diet (with high ratio of omega-6 to omega-3 fatty acids being 10 to 1). The other three groups were given food with a balanced 1 to 1 omega 6 to omega 3 ratio and two additional groups supplemented with DHA plus long chain omega-6 fatty acids. After three months of feeding, all the DHA supplemented groups were noted to have a lower accumulation of beta amyloid and tau protein. It is felt that these abnormal proteins may contribute to the development of memory loss in later years.

Finally, there was a study published regarding omega-3 supplementation in children with learning and behavioral problems. This study was published in the April 2007 edition of the Journal of the Developmental and Behavioral Pediatrics (5), where 132 children, between the ages of seven to twelve years old, with poor learning, participated in a randomized, placebo-controlled, double-blinded interventional trial. A total of 104 children completed the trial. For the first fifteen weeks of this study, the children were given polyunsaturated fatty acids (omega-3 and omega-6, 3000 mg a day), polyunsaturated fatty acids plus multi-vitamins and minerals or placebo. After fifteen weeks, all groups crossed over to the polyunsaturated fatty acids (PUFA) plus vitamins and mineral supplement. Parents were asked to rate their children's condition after fifteen and thirty weeks. After thirty weeks, parental ratings of behavior improved significantly in nine out of fourteen scales. The lead author of the study, Dr. Sinn, indicated the present study is the largest PUFA trial to date with children falling in the poor learning and focus range. The results support those of other studies that have found improvement in poor developmental health with essential fatty acid supplementation.[8]

Research in 2005-06 has suggested that the in-vitro anti-inflammatory activity of omega-3 acids translates into clinical benefits. Cohorts of neck pain patients and of rheumatoid arthritis sufferers have demonstrated benefits comparable to those receiving standard NSAIDs[citation needed].

Those who follow a Mediterranean-style diet tend to have higher HDL ("good") cholesterol levels.[9] Similar to those who follow a Mediterranean diet, Arctic-dwelling Inuit - who consume high amounts of omega-3 fatty acids from fatty fish - also tend to have increased HDL cholesterol and decreased triglycerides (fatty material that circulates in the blood). In addition, fish oil supplements containing EPA and DHA have been shown to reduce LDL ("bad") cholesterol and triglycerides. Finally, walnuts (which are rich in ALA) have been shown to lower total cholesterol and triglycerides in people with high cholesterol.[10]

[edit] Health risks

In a letter dated October 31, 2000 entitled Letter Regarding Dietary Supplement Health Claim for omega-3 Fatty Acids and Coronary Heart Disease, the United States Food and Drug Administration Center for Food Safety and Applied Nutrition, Office of Nutritional Products, Labeling, and Dietary Supplements noted that the known or suspected risks of EPA and DHA omega-3 fatty acids may include:

  • Increased bleeding can occur if overused (normally over 3 grams per day)
  • The possibility of hemorrhagic stroke
  • Oxidation of omega-3 fatty acids forming biologically active oxidation products
  • Reduced glycemic control among diabetics
  • Suppression of immune and inflammation responses, and consequently, decreased resistance to infections and increased susceptibility to opportunistic bacteria

Subsequent advices from the FDA and national counterparts have permitted health claims associated with heart health.

   Dietary supplementation with omega-3 PUFA increases adiponectin and attenuates ventricular remodeling and dysfunction with pressure overload.
   Duda MK, O'shea KM, Lei B, Barrows BR, Azimzadeh AM, McElfresh TE, Hoit BD, Kop WJ, Stanley WC.
   Division of Cardiology, Department of Medicine, University of Maryland, Baltimore, MD 21201, United States; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, United States.
   OBJECTIVE: Epidemiological studies suggest that consumption of omega-3 polyunsaturated fatty acids (omega-3 PUFA) decreases the risk of heart failure. We assessed the effects of dietary supplementation with omega-3 PUFA from fish oil on the response of the left ventricle (LV) to arterial pressure overload. METHODS: Male Wistar rats were fed a standard chow or a omega-3 PUFA-supplemented diet. After 1 week rats underwent abdominal aortic banding or sham surgery (n=9-12/group). LV function was assessed by echocardiography after 8 weeks. In addition, we studied the effect of omega-3 PUFA on the cardioprotective adipocyte-derived hormone adiponectin, which may alter the pro-growth serine-threonine kinase Akt. RESULTS: Banding increased LV mass to a greater extent with the standard chow (31%) than with omega-3 PUFA (18%). LV end diastolic and systolic volumes were increased by 19% and 105% with standard chow, respectively, but were unchanged with omega-3 PUFA. The expr ession of adiponectin was up-regulated in adipose tissue, and the plasma adiponectin concentration was significantly elevated. Treatment with omega-3 PUFA increased total Akt protein expression in the heart, but decreased the fraction of Akt in the active phosphorylated form, and thus did not alter the amount of active phospho-Akt. CONCLUSION: Dietary supplementation with omega-3 PUFA attenuated pressure overload-induced LV dysfunction, which was associated with elevated plasma adiponectin.
   PMID: 17643403 [PubMed - as supplied by publisher]

[edit] Warning for persons with Congestive Heart Failure (CHF)

Persons with congestive heart failure, chronic recurrent angina or evidence that their heart is receiving insufficient blood flow are advised to talk to their doctor before taking omega-3 fatty acids. It may be prudent for such persons to avoid taking omega-3 fatty acids or eating foods that contain them in substantial amounts.[11]

In congestive heart failure, cells that are only barely receiving enough blood flow become electrically hyperexcitable. This, in turn, can lead to increased risk of irregular heartbeats, which, in turn, can cause sudden cardiac death. Omega-3 fatty acids seem to stabilize the rhythm of the heart by effectively preventing these hyperexcitable cells from functioning, thereby reducing the likelihood of irregular heartbeats and sudden cardiac death. For most people, this is obviously beneficial and would account for most of the large reduction in the likelihood of sudden cardiac death. Nevertheless, for people with congestive heart failure, the heart is barely pumping blood well enough to keep them alive. In these patients, omega-3 fatty acids may eliminate enough of these few pumping cells that the heart would no longer be able to pump sufficient blood to live, causing an increased risk of cardiac death.[11]

[edit] Research frontiers

[edit] Autism

According to an Internet survey, approximately 30% of parents use omega-3 supplements as a therapy for children with autism.[12] There are currently only a few studies on the effectiveness of essential fatty acid supplementation as a treatment of autism and none of these has been well-controlled.[13][14][15][16] Bell and colleagues reported that parents of 18 children with autism who had been supplemented with fish oil for six months described improvements in overall health, cognition, sleep patterns, social interaction, and eye contact.[17] Another case report found that a child with autism given 540 mg of EPA per day over a four week period experienced a complete elimination of his previous anxiety about everyday events as reported by his parents and clinician.[18]

[edit] Low birth weight

In a study of nearly 9,000 pregnant women, researchers found women who ate fish once a week during their first trimester had 3.6 times less risk of low birth weight and premature birth than those who ate no fish. Low consumption of fish was a strong risk factor for preterm delivery and low birth weight.[19] However, attempts by other groups to reverse this increased risk by encouraging increased pre-natal consumption of fish were unsuccessful.[20]

[edit] Psychological disorders

Omega-3s are known to have membrane-enhancing capabilities in brain cells.[5] One medical explanation is that omega-3s play a role in the fortification of the myelin sheaths. Not coincidentally, omega-3 fatty acids comprise approximately eight percent of the average human brain according to Dr. David Horrobin, a pioneer in fatty acid research. Ralph Holman of the University of Minnesota, another major researcher in studying essential fatty acids, who gave it the name, surmised how omega-3 components are analogous to the human brain by stating that "DHA is structure, EPA is function."

A benefit of omega-3s is helping the brain to repair damage by promoting neuronal growth.[5] In a six-month study involving people with schizophrenia and Huntington's disease who were treated with EPA or a placebo, the placebo group had clearly lost cerebral tissue, while the patients given the supplements had a significant increase of grey and white matter.[21]

Consequently, the past decade of omega-3 fatty acid research has procured some Western interest in omega-3s as being a legitimate 'brain food.' Still, recent claims that one's intelligence quotient, psychological tests measuring certain cognitive skills, including numerical and verbal reasoning skills, are increased on account of omega-3s consumed by pregnant mothers remain unreliable and controversial. An even more significant focus of research, however, lies in the role of omega-3s as a non-prescription treatment for certain psychiatric and mental diagnoses and has become a topic of much research and speculation.

In 1998, Andrew L. Stoll, MD and his colleagues at Harvard University conducted a small double-blind placebo-controlled study in thirty patients diagnosed with bipolar disorder. Over the course of nine months, he gave 15 subjects capsules containing olive oil, and another 15 subjects capsules containing nine grams of pharmaceutical-quality EPA and DHA. In doing so, he was able to make the general distinction between the placebo group failing to improve while the Omega-3 group experienced a noticeable degree of recovery. Though Stoll believes that the 1999 experiment was not as optimal as it could have been and has accordingly pursued further research, the foundation has been laid for more researchers to explore the theoretical association between absorbed omega-3s and signal transduction inhibition in the brain.[22]

"Several epidemiological studies suggest covariation between seafood consumption and rates of mood disorders. Biological marker studies indicate deficits in omega-3 fatty acids in people with depressive disorders, while several treatment studies indicate therapeutic benefits from omega-3 supplementation. A similar contribution of omega-3 fatty acids to coronary artery disease may explain the well-described links between coronary artery disease and depression. Deficits in omega-3 fatty acids have been identified as a contributing factor to mood disorders and offer a potential rational treatment approach." (American Journal of Psychiatry 163:1098-1100, June 2006)

In 2006, a review of published trials in the American Journal of Clinical Nutrition found the evidence in those trials "provides little support" for the use of fish or the n–3 long-chain polyunsaturated fatty acids contained in them to improve depressed mood. The review recommended larger trials be performed.[23]

[edit] Dietary sources

[edit] Daily values

As macronutrients, fats are not assigned recommended daily allowances. Macronutrients have AI (Acceptable Intake) and AMDR (Acceptable Macronutrient Distribution Range) instead of RDAs. The AI for n-3 is 1.6 grams/day for men and 1.1 grams/day for women[24] while the AMDR is 0.6% to 1.2% of total energy.[25]

"A growing body of literature suggests that higher intakes of α-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) may afford some degree of protection against coronary heart disease. Because the physiological potency of EPA and DHA is much greater than that for α-linolenic acid, it is not possible to estimate one AMDR for all n-3 fatty acids. Approximately 10 percent of the AMDR can be consumed as EPA and/or DHA."[25]

There was insufficient evidence as of 2005 to set a UL (upper tolerable limit) for n-3 fatty acids.[24]

Researchers believe the ideal omega-6 intake should be no more than 4-5 times that of our omega-3 intake. The National Institutes of Health recently published recommended daily intakes of fatty acids, specific recommendations include 650 mg of EPA and DHA, 2.22 g/day of alpha-linolenic acid and 4.44 g/day of linoleic acid.

A perceived risk of fish oil omega-3 supplementation has been heavy metal poisoning by the body's accumulation of traces of heavy metals, in particular mercury, lead, nickel, arsenic and cadmium as well as other contaminants (PCBs, furans, dioxins), which potentially might be found especially in less-refined fish oil supplements.[citation needed]. The fish oil industry has successfully improved the quality of fish oils on the market. An independent test in 2006 of 42 fish oils on the US market by found that all of the products exceeded safety standards for potential contaminants. The FDA recommends that total dietary intake of omega-3 fatty acids from fish not exceed 3 grams per day, of which no more than 2 grams per day are from nutritional supplements.[2]

Historically, the Council for Responsible Nutrition (CRN) and the World Health Organization (WHO) have published acceptable standards regarding contaminants in fish oil. The most stringent current standard is the International Fish Oils Standard (IFOS). Fish oils that typically make this highest grade are those that are molecularly distilled under vacuum, and have virtually no measurable level of contaminants (measured parts per billion and parts per trillion).

Omega supplementation in food has been a significant recent trend in food fortification, with global food companies launching omega-3 fortified bread, pizza, yoghurt, orange juice, children's pasta, milk, confections and infant formula.

[edit] Fish

Early humans evolved eating inter-tidal shellfish, while living a shoreline existence in Africa.[26] Now, as then, inter-tidal herbivorous shellfish such as mussels and clams can help people reach a healthy balance of omega-3 and omega-6 fats in their diets.[26][27]

The most widely available source of EPA and DHA is cold water oily fish such as wild salmon, herring, mackerel, anchovies and sardines. The oil from these fish have a profile of around seven times as much omega-3 as omega-6. Farmed salmon, being grain fed, have a higher proportion of omega-6 than wild salmon. Other oily fish such as tuna also contain omega-3 in somewhat lesser amounts. Consumers of oily fish should be aware of the potential presence of heavy metals and fat-soluble pollutants like PCBs and dioxins which may accumulate up the food chain.[28] Some supplement manufacturers remove heavy metals and other contaminants from the oil through various means, such as molecular distillation (see above), which increases purity, potency and safety.

Even some forms of fish oil may not be optimally digestible. Of four studies that compare bioavailability of the triglyceride form of fish oil vs. the ester form, two have concluded that the natural triglyceride form is better, and the other two studies did not find a significant difference. No studies have shown the ester form to be superior although it is cheaper to manufacture.[29][30]

Although fish is a dietary source of omega-3 fatty acids, fish do not synthesize them; they obtain them from the algae in their diet. For this reason, there is often a significant difference in EPA and DHA concentrations in farmed vs wild caught fish.[citation needed]

[edit] Flax

Flax (aka linseed) (Linum usitatissimum) and its oil are perhaps the most widely available botanical source of omega-3. Flaxseed oil consists of ca. 55% ALA (alpha-linolenic acid). Flax, like chia, contains approximately three times as much omega-3 as omega-6.

15 grams of flaxseed oil provides ca. 8 grams of ALA, which is converted in the body to EPA and then DHA at an efficiency of (2%-15%), and (2%-5%) respectively.[31]

[edit] Botanical sources of omega-3 fatty acid

The table lists omega-3 content as the percentage of ALA in the seed oil, unless otherwise noted.

Common name Alternate name Linnaean name % Omega-3 Reference
Chia chia sage Salvia hispanica 64% [32]
Kiwifruit Chinese gooseberry Actinidia chinensis 62% [32]
Perilla shiso Perilla frutescens 58% [32]
Flax linseed Linum usitatissimum 55% [32]
Lingonberry cowberry Vaccinium vitis-idaea 49% [32]
Camelina Gold-of-pleasure Camelina sativa 36% [32]
Purslane portulaca Portulaca oleracea 35% [32]

[edit] Eggs

Eggs produced by chickens fed a diet of greens and insects produce higher levels of omega-3 fatty acids than chickens fed corn or soybeans.[33]

[edit] Other sources

Krill, which are small, shrimp-like zooplankton, also contain the omega-3 fatty acids EPA and DHA. One advantage of extracting omega-3s from krill, as opposed to sources higher in the food chain, is that krill contain fewer heavy metals and PCBs harmful to humans.[citation needed] However, in comparison to higher animals, they also contain fewer omega-3 fatty acids per gram.[citation needed]

Meat from grass-fed animals is often higher in omega-3 than meat from the corresponding grain-fed animal.[citation needed] The omega-6 to omega-3 ratio of grass-fed beef is about 2:1, making it a more useful source of omega-3 than grain-fed beef, which usually has a ratio of 4:1.[34] Commercially available lamb is almost always grass-fed, and subsequently higher in omega-3 than other common meat sources.[citation needed] Milk and cheese from grass-fed cows may also be good sources of omega-3. One UK study showed that half a pint of milk provides 10% of the recommended daily intake (RDI) of ALA, while a piece of organic cheese the size of a matchbox may provide up to 88%".[35]

The microalgae Crypthecodinium cohnii and Schizochytrium are rich sources of DHA (22:6 ω-3) and can be produced commercially in bioreactors. Oil from brown algae (kelp) is a source of EPA.

Acai palm fruit also contains omega-3 fatty acids.

Omega-3 capsules are sold in bottles for daily intake as supplements.

Walnuts are also a good source, as they are one of few nuts that contain a meaningful amount of omega-3s.

[edit] The omega-6 to omega-3 ratio

Clinical studies[1][36][37] indicate that the ingested ratio of omega-6 to omega-3 (especially Linoleic vs Alpha Linolenic) fatty acids is important to maintaining cardiovascular health.

Both omega-3 and omega-6 fatty acids are essential, i.e. humans must consume them in the diet. Omega-3 and omega-6 compete for the same metabolic enzymes, thus the omega-6:omega-3 ratio will significantly influence the ratio of the ensuing eicosanoids (hormones), (e.g. prostaglandins, leukotrienes, thromboxanes etc.), and will alter the body's metabolic function. Generally, grass fed animals provide more omega 3 than do grain fed animals which produce relatively more omega 6. Metabolites of omega-6 are significantly more inflammatory (esp. arachidonic acid) than those of omega-3. This necessitates that omega-3 and omega-6 be consumed in a balanced proportion; the ideal ratio of omega-6:omega-3 being from 3:1 to 5:1. Studies suggest that the evolutionary human diet, rich in seafood, nuts and other sources of omega-3, may have provided such a ratio.[36]

Simopoulos, et al[38] recommend daily intakes of three omega-3 forms: 650 mg of EPA and DHA, and 2.22 grams of ALA, and one omega-6 form: 4.44 grams of LA. This translates to a 3:2 omega-6 to omega-3 ratio. (i.e. 1.5:1)

Typical Western diets provide ratios of between 10:1 and 30:1 - i.e., dramatically skewed toward omega-6. Here are the ratios of omega-6 to omega-3 fatty acids in some common oils: canola 2:1, soybean 7:1, olive 13:1, sunflower (no omega-3), flax 1:3[39] cottonseed (almost no omega-3), peanut (no omega-3), grapeseed oil (almost no omega-3) and corn oil 46 to 1 ratio of omega-6s to omega-3s.[40] It should be noted that olive, peanut and canola oils consist of approximately 80% monounsaturated fatty acids, (i.e. neither omega-6 nor omega-3) meaning that they contain relatively small amounts of omega (3 & 6) fatty acids. Consequently, the omega-6 to omega-3 ratios for these oils (i.e. olive, canola and peanut oils) are not as significant as they are for corn, soybean and sunflower oils.

[edit] See also

[edit] Notes and references

  1. ^ a b W.E.M. Lands (1992). Biochemistry and physiology of n-3 fatty acids. FASEB J 6: 2530-2536.
  2. ^ a b US Food and Drug Administration (September 8, 2004). FDA Announces Qualified Health Claims for Omega-3 Fatty Acids. Press release. Retrieved on 2006-07-10.
  3. ^ Catherine H. MacLean, MD, PhD et al (January 2006). "Effects of Omega-3 Fatty Acids on Cancer Risk". Journal of the American Medical Association 295 (4): 403-415. PMID 16434631. Retrieved on 2006-07-07. 
  4. ^ Lee Hooper et al (April 2006). "Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review" (pdf). British Medical Journal 332: 752-760. DOI:10.1136/bmj.38755.366331.2F. Retrieved on 2006-07-07. 
  5. ^ a b c Bijal Trivedi The good, the fad, and the unhealthy New Scientist, 23 September 2006, pp 42-49.
  6. ^ Wang C, Harris WS, Chung M, et al. n-3 fatty acids from fish or fish-oil supplements but not a-linoleic acid, benefit cardiovascular outcomes in primary and secondary prevention studies: a systematic review. Am J. Clin Nutr 2006;84:5-17
  7. ^ Mozaffarian D, & Rimm EB. Fish Intake, Contaminants, and Human Health: Evaluating the Risks and the Benefits. JAMA, October 18, 2006—Vol 296, No. 15
  8. ^ 1. MCKENNEY, J. and SICA, D, Prescription omega-3 fatty acids for the treatment of hypertriglyceridemia, American Journal of Health-System Pharmacy. 646:595-605, March 15, 2007 2. Yokoyama M et al., Effects of eicosapentaenoic acid on major coronary events in hypercholesterolemic patients (JELIS): a randomized open-label, blinded endpoint analysis, Lancet 2007 3. Damsgaard C, Lauritzen L, Kjær T, Holm P, Fruekilde M, Michaelsen K and Frøkiær H, Fish Oil Supplementation Modulates Immune Function in Healthy Infants, J. Nutr. 137:1031-1036, April 2007 4. LaFerla F, Martinez-Coria H, Khashwji H, Hall E, Yurko-Mauro K and Ellis L, Journal of Neuroscience, April 18, 2007, Volume 27, Number 16 5. Sinn, N and Bryan, J, Effect of Supplementation with Polyunsaturated Fatty Acids and Micronutrients on Learning and Behavior Problems Associated with Child ADHD, Journal of Developmental & Behavioral Pediatrics. 28(2):82-91, April 2007 6. Lee D, Lee I, Jin S, Steffes M, Jacobs D, Association Between Serum Concentrations of Persistent Organic Pollutants and Insulin Resistance Among Nondiabetic Adults, Diabetes Care 30:622-628, 2007
  9. ^ Kris-Etherton P, Eckel RH, Howard BV, St. Jeor S, Bazzare TL. AHA Science Advisory: Lyon Diet Heart Study. Benefits of a Mediterranean-style, National Cholesterol Education Program/American Heart Association Step I Dietary Pattern on Cardiovascular Disease. Circulation 2001;103:1823
  10. ^ Zambón D, Sabate J, Munoz S, et al. Substituting walnuts for monounsaturated fat improves the serum lipid profile of hypercholesterolemic men and women. Ann Intern Med. 2000;132:538-546.
  11. ^ a b This advice has now been updated in favour of omega 3 intake by the UK's medical committee, NICE ( see below ). Ornish, Dean. "The Dark Side of Good Fats", Newsweek, 2006-05-02, p. 2. Retrieved on 2006-10-06. 
  12. ^ Green, V.A., K.A. Pituch, J. Itchon, A. Choi, M. O'Reilly, J. Sigafoos, "Internet survey of treatments used by parents of children with autism," Res Dev Disabil, 2006, 27(1):70-84.
  13. ^ Young, G., and J. Conquer. 2005. "Omega-3 fatty acids and neuropsychiatric disorders." Reprod.Nutr.Dev 45(1):1-28.
  14. ^ Genuis, S.J.a.G.K.S. 2006. "Time for an oil check: the role of essential omega-3 fatty acids in maternal and pediatric health." Journal of Perinatology 26:359-365.
  15. ^ Richardson, A.J. 2006. "Omega-3 fatty acids in ADHD and related neurodevelopmental disorders." Int.Rev.Psychiatry 18(2):155-172.
  16. ^ Richardson, A.J., and M.A. Ross. 2000. "Fatty acid metabolism in neurodevelopmental disorder: a new perspective on associations between attention-deficit/hyperactivity disorder, dyslexia, dyspraxia and the autistic spectrum." Prostaglandins Leukot.Essent.Fatty Acids 63(1-2):1-9.
  17. ^ Bell, J.G., et al. 2004. "Essential fatty acids and phospholipase A2 in autistic spectrum disorders." Prostaglandins Leukot.Essent.Fatty Acids 71(4):201-204.
  18. ^ Johnson, S.M., and E. Hollander. 2003. "Evidence that eicosapentaenoic acid is effective in treating autism." J Clin Psychiatry 64(7):848-849.
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