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Sunday, June 2, 2013

Understanding Important Polyunsaturated Fatty Acids and Its Requirement in Humans

Posted by Dr Prahallad Panda on 7:14 PM Comments

Fatty acids are the building blocks of Fats; fats enzymatically get degraded to fatty acids in humans for absorption to body.
Fatty acids are of many categories; some are preserved and burnt for energy requirement, whereas some other take part in essential processes of body as well as incorporated as building blocks of tissue.
Saturated & Unsaturated Fats:
Fats can be saturated, when it can no more accept molecules like hydrogen (H); or can be unsaturated, where able to accept some molecule/atom. Biochemically speaking, unsaturated fatty acids have some double bonds between atoms/molecules of their backbone, whereas saturated ones have non.
Polyunsaturated (PUFA) & Mono-unsaturated Fats (MUFA):
Unsaturated fatty acids are more important, and can have many unsaturated bonds to be called as polyunsaturated fatty acids (PUFA) or single bonds to be called as mono-unsaturated fatty acids (MUFA).
Both plants and animals are good source of fatty acids. But, some fatty acids are present more in quantity in plants and some other in animals.
Human can synthesize some longer-chain fatty acids (LCA) from the smaller fatty acids as regards to content of their carbon atoms.
Essential Fatty Acids:
Those fatty acids, which cannot be synthesized in body are called essential fatty acids (EFA), require to be supplemented from outside. Absolutely essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA); whereas body has limited ability to synthesize some other fatty acids e.g. Docosahexaenoic acid (DHA) and Ecosopentaenoic acid (EPA).
Both linoleic acid and alpha-linolenic acid are found in abundance in plants and animals; whereas docosahexaenoic acid is mainly found in oily sea fishes.
Linoleic acid is a omega-6 (Or n-6) fatty acid; alpha-linolenic and docosahexaenoic acid (Longer chain) are omega-3 (Or n-3) fatty acids.
Omega Fatty Acids:
Fatty acids are called omega 6, 3 or any other number like 9, depending on the position of first unsaturated bond from the methyl terminal (CH2) (termed as omega) of the backbone.
Cis & Trans Fats:

Space-filling model of the α-Linolenic acid mo...
Space-filling model of the α-Linolenic acid molecule, an unsaturated fatty acid. Colour code (click to show) : Black: Carbon, C : White: Hydrogen, H : Red: Oxygen, O (Photo credit: Wikipedia)

Also, fatty acids can be called cis or trans depending on the configuration of the relative position of hydrogen atom to unsaturated bonds; if those are on the same sides, termed as cis and if are on opposite sides, are termed as trans. Cis fat are good for heath. Cis fats are flexible, have bends; whereas trans fats are rigid, having no bends.
Balance of Fat:
There should be an ideal proportion of omega-6 fatty acid to omega-3 fatty acid in body to maintain balance, usually 4 : 1, which should not be disturbed.
Sea foods are excellent source of protein and oils. Seafood-derived oils are rich in marine n-3 PUFA, particularly DHA and EPA.
Algae are the primary producers of DHA and EPA in the ecosystem. Fish consume algae and are therefore rich in DHA and EPA.
Terrestrial sources rich in n-3 PUFA include flax seed, canola, walnut and soybean oils, which contain the 18-carbon ALA as the major n-3 PUFA.
Alpha-linolenic acid (ALA) Walnuts, flaxseed oil, soy-bean, and canola oil
Eicosapentaenoic acid (EPA) Oily fish and fish oils
Docosahexaenoic acid (DHA) Oily fish and fish oils and algae oils
Linoleic acid (LA) Corn, safflower, soybean, cottonseed, and sunflower oils Gamma-linolenic acid (GLA) Evening primrose oil, borage oil, and black current seed oil.
Arachidonic acid (AA) Meat, poultry, and eggs, fish
Oleic Acid (OA) Olive oil, canola oil, nuts.
In humans, ALA deficiency is associated with sensory neuropathy, impaired visual activity and learning deficiency.
DHA and EPA can reverse n-3 PUFA deficiency. DHA is the most abundant n-3 PUFA in tissues and is generally considered to be the most essential n-3 PUFA. n-3 PUFA are present in all membranes and are incorporated into phospholipids, sphingolipids and plasmogens.
They are also most concentrated in sperm, brain and retina. DHA is several hundred times more abundant than EPA in the brain and retina cells. In adipose tissue, ALA is the most abundant n-3 PUFA, although it comprises only about 1% of FA in this tissue.
Recommendations on Daily Allowance:
The American Heart Association's Nutrition Committee strongly advises these fat guidelines for healthy Americans over age 2:
  • Limit total fat intake to less than 25–35 percent of your total calories each day;
  • Limit saturated fat intake to less than 7 percent of total daily calories;
  • Limit trans fat intake to less than 1 percent of total daily calories;
  • The remaining fat should come from sources of monounsaturated and polyunsaturated fats such as unsalted nuts and seeds, fish (especially oily fish, such as salmon, trout and herring, at least twice per week) and vegetable oils; and
  • Limit cholesterol intake to less than 300 mg per day, for most people. If you have coronary heart disease or your LDL cholesterol level is 100 mg/dL or greater, limit your cholesterol intake to less than 200 milligrams a day.
For example, a sedentary female who is 31–50 years old needs about 2,000 calories each day. Therefore, she should consume less than 15 g saturated fat, less than 2 g trans fat and between 56 and 77 grams of total fat each day (with most fats coming from sources of polyunsaturated and monounsaturated fats, such as fish, nuts, seeds and vegetable oils).
In typical adult females and males, 2 % of the total daily energy intake should be derived from omega-6 PUFA and 0.5 % from omega-3 PUFA. This corresponds to a daily intake of approximately 6 g/day (5 g omega-6 PUFA/day + 1 g omega-3 PUFA/day) for women and 8 g/day (6.4 g omega-6 PUFA/day + 1.6 g omega-3 PUFA/day) for men.
In 2003, the International Society for the Study of Fatty Acids and Lipids (ISSFAL, published its recommendations for intake of PUFA in healthy adults. The scientists suggested for cardiovascular health a minimum intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) combined of 500 mg/day. 

DHA Molecule
DHA Molecule (Photo credit: Wikipedia)
In 2009, The European Food Safety Authority (EFSA) published its recommendations for PUFA:
  • an omega-3 fatty acid intake of 2 g/day alpha-linolenic acid (ALA) and 250 mg/day long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
  • an omega-6 fatty acid intake of 10 g/day linoleic acid (LA).
Compliance to Supplementation:
So, somehow one should get sufficient n-3 PUFA, possibly from fish; but problem is with vegetarian population.
Taking fish oil supplementation may not be possible for various reasons; one has to take as many as 4-6 capsules of fish oil to meet the recommended level of DHA and EPA, which is practically not patient friendly; the disagreeable eructation that occurs after taking the capsule may not be tolerated by some; and some may not like to take it citing religious reasons.
Fish is usually eaten after cooking. Because fat may be added during cooking, the cardiac benefits of fish consumption depend on how it is cooked. Consumption of fried fish is not associated with lower prevalence of Coronary Heart Disease (CHD).
In a study. people who consumed fried fish more than once a week had a 44% higher risk of ischaemic stroke than those who consumed fried fish once per month. Frying fish with oil in high temperature transforms the good fatty acids to bad ones.
Broiled or baked fish was associated with lower stroke and CHD rates, it the study. Processed oils may not be good too, as some unsaturated fatty acids may get transformed in the process of purification; and added chemicals may harm.
Therefore, a balanced diet with good amount of oil from plant source in vegetarian population may be satisfactory; probably body finds alternative way to produce DHA from available n-3 fatty acids (Like LA).
For non-vegetarian population oily fish supplementation may be very good to avoid PUFA deficiency diseases; which should be eaten broiled or baked.
In both vegetarian and non-vegetarian population, diet should be suitably planed in lieu of searching for outside supplementation.
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