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Fat

Body fat stores energy and insulates against cold. Fat is also an important constituent of the brain and nerves, but most importantly it is part of the membrane of all cells.

Most fats are fatty acids, which may be attached to glycerol as triglycerides or phospholipids, which also have a phosphate-group attached. The fatty acids may be saturated (having no double bindings) or unsaturated (having one or more double bindings). Most saturated fats are solid (like lard), but the unsaturated fats are fluid (like oils) at body temperature.

Cholesterol is a special fat, which is produced in the body where it is a precursor for important molecules such as bile acids, steroid hormones, sex hormones and vitamin D, which are necessary for good health!

Of the fats only a few cannot be produced in the body. They are the essential fatty acids having the first double binding in position 3 (omega-3 fatty acids) or in position 6 (omega-6 fatty acids). All double bindings are in cis formation (as opposed to trans formation). Here is more about the harmful trans fatty acids.

The omega-3 fatty acids include alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

The omega-6 fatty acids include linoleic acid (LA) and arachidonic acid (AA).

The essential fatty acids must be supplied with the food. All other fats are not essential and need not be present in the diet.

The essential fatty acids are important for the formation of healthy cell membranes, proper development and functioning of the brain and nervous system, and production of hormone-like substances called eicosanoids (thromboxanes, leukotrienes and prostaglandins) being responsible for regulating blood pressure, blood viscosity, vasoconstriction, immune and inflammatory responses.

The eicosanoids typically have a short active lifetime starting with synthesis from fatty acids and ending with metabolic elimination by enzymes. However, if the rate of synthesis exceeds the rate of metabolic elimination, the excess eicosanoids may have deleterious effects.

If both omega-3 and omega-6 fatty acids are present they will “compete” in the production of their eicosanoids. So if the omega-6 outnumber the omega-3 fatty acids, relatively more omega-6 derived eicosanoids will be synthesized.

The omega-6 eicosanoids are more inflammatory than the omega-3 eicosanoids, which are often referred to as anti-inflammatory. In fact the omega-3 eicosanoids are just less inflammatory and they are being produced at a much slower rate.

So, excess omega-6 fatty acids interfere with the health benefits of omega-3 fatty acids.

A high proportion of omega−6 to omega−3 fatty acids in the diet is associated with increased risk of inflammatory activity as in thrombotic disease, cardiovascular disease, type 2 diabetes, obesity, metabolic syndrome, rheumatoid arthritis, asthma, cancer, psychiatric disorders (depression, schizophrenia), and autoimmune diseases.

The excess synthesis of inflammatory omega-6 eicosanoids have been attempted to be controlled medically (e.g. COX-1 and COX-2 inhibitors (aspirin, nonsteroidal antiinflammatory drugs (NSAID)), LOX inhibitors (asthma medication like montelukast, pranlukast and zafirlukast) and antimania medications (lithium, valproate and carbamazepine) targeting the arachidonic acid cascade in the brain.

Obviously, the simplest way to maintain good health would be to consume fewer omega-6 and more omega-3 fatty acids.    

Omega-3 fatty acids play a crucial role in brain function, as well as in normal cell growth and development.

Omega-3 fatty acids are highly concentrated in the brain and appear to be important for cognitive (memory and performance) and behavioral functions.

They are also important in maintaining the health of the heart and they may reduce the risk of cancer and arthritis. They also reduce inflammation.

Omega-6 fatty acids help stimulate skin and hair growth, maintain bone health, regulate metabolism, and maintain the reproductive system.

Omega-6 fatty acids tend to promote inflammation. In fact, some studies suggest that elevated intakes of omega-6 fatty acids may play a role in the Complex Regional Pain Syndrome.

Sources

The health effects of omega-3 fatty acids come mostly from EPA and DHA. The richest sources of these are oily fish like sardines, herring, salmon, trout, and mackerel.

Whitefish like cod, haddock and flatfish contain much less omega-3 fatty acid.

Important sources of ALA are oils from flaxseeds, rapeseeds, soybeans, pumpkin seeds, purslane, and walnuts.

Please note that ALA from plant sources needs to be converted in the body to EPA and DHA, and many people do not make these conversions very effectively.

Furthermore, the absorption of essential fatty acids is much less from plant than animal sources.

For these reasons oily fish would be the recommended primary source. You can see data on the content of omega-3 and omega-6 fatty acids in selected foods here.

Fish oil supplements have passed safety standards for potential contaminants including heavy metals (mercury, lead, nickel, arsenic, and cadmium).

These metals do not accumulate in the oil but may bind with the protein in the fish flesh. However, researchers from Harvard’s School of Public Health finds that the benefits of fish intake generally far outweigh the potential risks.

Daily intake

The average modern Western diet provides plenty of omega-6 fatty acids but smaller amounts of omega-3 fatty acids, the ratios of omega-6 to omega-3 being in excess of 10 : 1, in some cases even as high as 30 : 1. The optimal ratio is thought to be 4 : 1 to 2 : 1 or even lower.

Thus the general recommendation would be to increase intake of omega-3 and decrease intake of omega-6 fatty acids.

An amount of 3 grams daily of omega-3 fatty acids is considered safe.

Deficiency

Symptoms of omega-3 fatty acid deficiency include fatigue, poor memory, dry scaly skin, arthritis, heart problems, mood swings or depression, and poor circulation.

Omega-6 fatty acid deficiency symptoms can include arthritis like symptoms, skin eruptions, slow wound healing, behavioral disturbances and heart and circulatory problems. Pregnant women may experience miscarriages and men may become sterile.

However it may be difficult to attribute certain symptoms to a specific omega-3 or omega-6 fatty acid deficiency since many symptoms may have a relation to imbalance between the two types of essential fatty acids in the diet.

Excess

As mentioned above the general problem with the average Western diet is the dominance of omega-6 over omega-3 fatty acids. Doses of 6.6 grams of omega-3 fatty acids (EPA 4.4 grams DHA 2.2 grams) daily have been tolerated without major side effects. However, larger amounts of fish oil may increase the risk of bleeding.   

References: 1 , 2 , 3 , 4 , 5

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