Omega-3 fatty acid

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Omega-3 fatty acids are polyunsaturated fatty acids found in certain fish tissues, and in vegetable sources such as flax seeds, hemp seeds, walnuts, and canola oil — though some sources contain other substances which may counteract the beneficial Omega-3 (see sections Omega-3 - Omega-6 balance, and Dietary sources below). Such fatty acids are also more prevalent in grass-fed or pasture-finished livestock, compared to those fed a diet high in grains.

Omega-3 fatty acids are classed as essential fatty acids. These fatty acids were originally designated as "Vitamin F", until it was realized that they must be classified with the fats.

Contents
1 Omega-6 vs Omega-3
2 Health effects of omega-3 fatty acids
3 Known and suspected risks of omega-3 fatty acids
4 Dietary sources of Omega-3

4.1 Useful sources of Omega-3

4.1.1 Grass fed ruminants

4.2 Oils with little impact on Omega-3 to Omega-6 balance
4.3 Sources which in fact promote an imbalance between Omega-3 and Omega-6

5 Chemistry
6 Biological significance of omega-3 (and omega-6) fatty acids
7 References
8 See also
9 External links

Omega-6 vs Omega-3

Another essential fatty acid is Omega-6. But while essential to the diet, recent trends in Western food preparation and ingredients have resulted in much more than necessary of Omega-6 being consumed by typical Westerners.

And studies have shown that while both Omega-3 and Omega-6 should be consumed in satisfactory quantities, it is also very important that they be consumed in the correct proportions — in fact we should try for better than 4 or 5:1 Omega-6 to Omega-3.

Many sources of Omega-3 also contain Omega-6, making the task somewhat tricky.

"Typical American" diets have been found to have ratios between 10:1 and 30:1 in favour of Omega-6 — that is, dramatically skewed in toward Omega-6.

US National Institutes of Health recommends 650 mg of EPA and DHA, 2.22 g/day of alpha-linolenic acid, all of which are Omega-3 fatty acids, and 4.44 g/day of linoleic acid, aka Omega-6. (see section Biological significance of omega-3 (and omega-6) fatty acids)

Source

It has been conjectured that the diet in the human environment of evolutionary adaptedness may have been rich in seafood, nuts and other sources of vegetable omega-3. This may have provided a ratio close to 1:1. An optimal ratio for cardiovascular health is thought to be 4:1 or less, but the introduction of processed foods with very high ratios of omega-6 to omega-3 in the last fifty years is probably partially responsible for the fact that heart disease is the number one killer in the United States today.

The reason these compounds need to be consumed in balance may be because many of the same enzymes are used in digesting both substances — and are in short supply. If a lot of Omega-6 is consumed, it uses up most of the enzymes on digesting this. [1]

Health effects of omega-3 fatty acids

Many studies have demonstrated health benefits of increasing Omega-3 fatty acids in deficient diets, or corresponding detrimental effects for ongoing deficiencies of the nutrient. See the list of references at the end of this article for some of these studies.

Known and suspected risks of omega-3 fatty acids

In its letter entitled Letter Regarding Dietary Supplement Health Claim for Omega-3 Fatty Acids and Coronary Heart Disease the U. S. 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 omega-3 fatty acids may include:

In addition, another potential risk is the possibility of vitamin poisoning from taking large doses of supplements which contain significant amounts of vitamins (particularly vitamin D) in addition to omega-3 fatty acids, or heavy metal poisoning by the accumlation of traces of heavy metals, particularly mercury, in concentrated fish oil supplements.

For these reasons, the FDA recommends that total dietary intake of omega-3 fatty acids be limited to 3g/day, of which no more than 2g/day should come from nutritional supplements. [2] However, many nutritionists recommend more than this, pointing out that the studies used by the FDA only indirectly show that high doses of omega-3 fatty acids are harmful.

Dietary sources of Omega-3

Useful sources of Omega-3

The best known source of Omega-3 is fish oil from coldwater, fatty fish, such as sardines which contain large amounts of Omega-3, and have a profile of around seven times as much Omega-3 as Omega-6. Larger fatty fish such as tuna also contain Omega-3, but should perhaps not be eaten in great quantities due to the potential for heavy metals which accumulate up the food chain. Additionally, with the greater lifespan of the larger fish more toxic heavy metals may accumulate. Many supplement manufacturers claim to filter heavy metals from their products. Even some forms of fish oil may not be optimally digestible — at least, according to this sales blurb.

Flax (aka linseed) or its oil is another very good source, and may be the best source for vegetarians. Flax contains a significant amount of Omega-6, but has around three times as much Omega-3 as Omega-6. Warning: A study on how effectively the Omega-3 in flax was converted and utilised in breast milk indicated that flax Omega-3 was not transferred. [3] This may indicate that flax is not a useful source of the nutrient, and certainly should not be relied on by pregnant mothers, as Omega-3 is essential to the formation of the developing child's brain.

Perilla (shiso) probably has even more Omega-3 and less Omega-6 than flax.

Pumpkin seeds have a high proportion of Omega-3 compared with Omega-6, so may be useful to vegetarians in rectifying an imbalance, but flax would be much better.

Grass fed ruminants

Some animal species which in the wild eat grass have been found to produce significantly less Omega-3 if they are fed a grain diet, as is popular in Western livestock production of sheep and cattle (known as ruminants because of the way their stomachs process grass). Organicly raised animals may be better than non-organic ones, but if fed on grain will not be as good as grass-fed ones. [4]

Related to Omega-6 and Omega-3 is Conjugated Linoeic Acid (CLA) and this is also higher in grass fed beef rather than grain fed.

Organically raised, or grass-fed beef, is a good source of Omega-3, and produce a more favourable ratio of Omega-6 to Omega-3 than grain fed specimens. [5] The ratio is about 2:1, making this a useful secondary source of Omega-3.

Organic milk, and particularly organic cheese, is a good source of Omega-3, with a ratio of 1:1 with Omega-6. [6] Non-organically produced milk may contain only about a third of the Omega-3 though. One UK study showed a half-pint of milk gives 10% of their recommended daily intake (RDI) of Omega-3, while a "matchbox sized piece of organic cheese will give you up to 88%". [7]

Oils with little impact on Omega-3 to Omega-6 balance

Olive oil has more Omega-6 than Omega-3, but has very little of either. It burns easily though, so is not a good all-round oil for cooking. (Burnt oils contain large amounts of trans- fatty acids, which are detrimental to health.)

(Note regarding the above statement: Claims that trans-fat can be created simply by heating oils have been challenged [8] by Mary G. Enig, an expert on the subject of trans-fats and one of the first researchers to sound the alarm about trans-fats in the American diet. She also states that "Those fats and oils that are appropriate for cooking or sautéing and will withstand fairly high temperatures are those that have been in use for thousands of years, including olive oil...")

Ghee (clarified butter), and coconut and palm oil, all have some Omega-6 and little-or-no Omega-3, but the Omega-6 is in such small quantities that they are generally not going to impact the dietary balance significantly. They are also tolerant of high temperatures, so are a good choice for general purpose cooking (but they are saturated fats, so may be unsuitable for some consumers).


Shea nut seems also not to have great quantities of Omega-6.

Sources which in fact promote an imbalance between Omega-3 and Omega-6

Walnuts contain large amounts of Omega-3, but are also high in Omega-6, so are in fact likely to be detrimental in a diet already rich in Omega-6.

Canola oil (aka rapeseed oil) is recommended by many, but in fact contains large enough quantities of Omega-6, (two to three times as much as the amount of Omega-3), making it unsuitable for restoring an imbalance of these two nutrients. Canola may be useful as a general purpose oil to people who need to avoid saturated fats, as it will skew the balance significantly less than the following oils.

Oils of sunflower, safflower, sesame, corn, rice-bran, cottonseed (frequently used in fast food deep frying), soy, peanut (groundnut), grapeseed and wheat are all relatively high in Omega-6 and low in Omega-3, so if used in significant quantities, may be detrimental to diets already rich in Omega-6. These sources are why western diets are so badly balanced with respect to Omega-3 vs Omega-6, soy or wheat are included in almost all processed foods, and most vegetable oils used in commercial cooking are one of these. (Some forms of Sunflower oil may actually be OK, but you tell me how to know.)

Sources [9], [10], [11]

Chemistry

The term "omega-3" signifies that the first double bond in the carbon backbone of the fatty acid, counting from the end opposite the acid group, occurs in the third carbon-carbon bond. This way of counting was introduced by physiologists. Chemists would normally count the position of the double bond from the acid end position (the alpha positions). However by counting from the other end, physiologists revealed the similarity between fatty acids of diverse length.

Like all polyunsaturated fatty acids, the omega-3 fatty acids have minimum 2 and maximum 6 double bonds in a carbon chain that ranges from 18 to 22 carbon atoms.

In natural conditions, the double bonds are in the cis-conformation, with the two hydrogen atoms at the same side of the double bond. This characteristic, along with the fact that every double bond is separated by a methyl group, explains the 3D-structure and the properties of omega-3 and omega-6 fatty acids as well as those of the phospholipids that contain them. With every additional cis bond, the carbon chain will change direction, so that the long omega-3 and omega-6 chain structure is not one long straight chain, but a twisted molecule. This simple difference explains a host of biological phenomena in structures that are rich in polyunsaturated fatty acids, especially the lipid bilayer of the cell membrane.

Biological significance of omega-3 (and omega-6) fatty acids

Common omega-3 fatty acids in the body are:

Gamma-linolenic acid is an omega-6 fatty acid.

Arachidonic acid, an omega-6 fatty acid (C20:4, n-6), is one of the most important precursors of anti-inflammatory prostaglandins. These precursors are jointly referred to as eicosanoids since they have 20 carbon atoms (eicosa is Greek for 20).

Since the metabolism of omega-3 and omega-6 fatty acids shares common enzymes (elongase and desaturase enzymes), its is widely accepted that both types of polyunsaturated fatty acids behave as competitive substrates. However, the desaturation of omega-3 fatty acids leads to less inflammatory eicosanoids than arachidonic acid. It is also likely that omega-3 fatty acids such as eicosapentaenoic acid have very specific biological activities. EPA supplementation inhibits or attenuates the pro-inflammatory cascade that follows on the enzymatic release of free arachidonic acid from the cell membrane. In this respect, some researchers have uncovered interesting parallels between the biological effect of aspirin, NSAIDs (non-steroidal anti-inflammatory drugs) and fish oil.

The scientific and commercial attention given to the effect of omega-3 fats on inflammation and inflammatory signals has increased significantly since the 1990s.

References

See also

External links

See also: Omega-3 fatty acid, Arachidonic acid, Aspirin, Bioaccumulation, CLA, Canola oil, Carbon