I need to do this for my Health homework but I have no idea what to say! Do you think it means I should describe what they are? Gotta love people who just copy the Wikipedia listing to answer a question. LOL!
Omega 3 fatty acids are primarily the ALA, EPA, and DHA. They are commonly found in flax oil and fish oil in the highest concentrations.
If you are doing your homework, the questions at the end of the chapters (or in tests) are usually referring to answers listed in the assigned chapters. You should be able to browse over the section headings and bolded titles for each section to find the exact quote your teacher is looking for.
Oh, and in the future, it's best to do your homework on your own and find the answers in whatever assigned reading your teacher gives you or what's listed on your syllabus. The term omega-3 (aka "n-3", "蠅-3") signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (蠅) of the carbon chain.
Omega-3 fatty acids which are important in human nutrition are: 伪-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 蠅-3 fatty acids are largely mediated by their interactions with the 蠅-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. Extensive details of physiology, metabolism and nutrition are provided in his 2005 book, "Fish, Omega-3 and Human Health". A 2007 book by Evelyn Tribole, "The Ultimate Omega-3 Diet" extends this discussion with food contents and recipies by which people can balance dietary intakes of omega-3 and omega-6 fats.
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 纬-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.[citation needed]
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.[citation needed]
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.[citation needed]
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.[citation needed]
There was yet another study on omega-3 fatty acids 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.[citation needed]
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 less heart disease, higher HDL ("good") cholesterol levels [9] and higher proportions of omega-3 in tissue highly unsaturated fatty acids [10]. 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 higher proportions of omega-3, increased HDL cholesterol and decreased triglycerides (fatty material that circulates in the blood) and less heart disease. Eating walnuts (which have several-fold more omega-3 ALA than omega-6 LA) was reported to lower total cholesterol by 4% relative to controls when people also ate 27% less cholesterol.[11]
[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:
There have been reports that increased bleeding can occur if overused (normally over 3 grams per day) by a patient who is also taking aspirin or coumadin (warfarin). However, this is disputed.[1]
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.
[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.[12]
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 by incrising the blood flow, 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.
[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.[13] 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.[14][15][16][17] 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.[18] 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.[19]
[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.[20] However, attempts by other groups to reverse this increased risk by encouraging increased pre-natal consumption of fish were unsuccessful.[21]
[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.[22]
In the prefrontal cortex (PFC) of the brain, low brain omega-3s are thought to lower the dopaminergic neurotransmission in this brain area, possibly contributing to the negative and neurocognitive symptoms in schizophrenia. This reduction in dopamine system function in the PFC may lead to an overactivity in dopaminergic function in the limbic system of the brain which is suppressively controlled by the PFC dopamine system, causing the positive symptoms of schizophrenia (Ohara, 2007). This mechanism may explain why omega-3 supplementation shows effects against both positive, negative and neurocognitive symptoms in schizophrenia.
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.[23]
"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鈥? long-chain polyunsaturated fatty acids contained in them to improve depressed mood. The review recommended larger trials be performed.[24]
[edit] Short bowel syndrome
Case reports show that an omega-3 rich emulsion, Omegaven, reduced the risk of liver damage in this condition.
[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[25] while the AMDR is 0.6% to 1.2% of total energy.[26]
"A growing body of literature suggests that higher intakes of 伪-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 伪-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."[26]
There was insufficient evidence as of 2005 to set a UL (upper tolerable limit) for n-3 fatty acids.[25]
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 www.consumerlab.com found that all of the products exceeded safety standards for potential contaminants.[27] 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 ate inter-tidal shellfish, while living a shoreline existence in Africa.[28] 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.[28][29]
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.[30] 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.[31][32]
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
Six times richer than most fish oils in omega-3[33], 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.[34] You can find all the information you need on Omega-3's at Wikipedia.org Enter in the Search box - Omega 3 and the result should provide sufficient information for most people's needs. |
