Omega-3 fatty acids which are important in human nutrition are: alpha-linolenic acid (18:3, ALA),
eicosapentaenoic acid (20:5, EPA), and docosahexaenoic acid.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.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.
Omega-3 fatty acids are polyunsaturated fatty acids classified as essential because they cannot be synthesized in the body; they must be obtained from food.
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).
Those who follow a Mediterranean-style diet tend to have higher HDL ("good") cholesterol levels.
Similar to those who follow a Mediterranean diet, Inuit Eskimos, 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.
The most widely available source of EPA and DHA is cold water oily fish such as 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. 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.
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.
For older adults, fish oils help the heart by regulating its electrical activity, a new study indicates.And just a couple of meals a week of the right kind of fish -- rich in omega-3 fatty acids, baked or boiled, but not fried -- will do the job, according to the report in the Aug. 1 Journal of the American College of Cardiology.
The finding "supports studies suggesting that fish intake reduces the risk of sudden death," said
study lead author Dr. Dariush Mozaffarian, a cardiologist and instructor of medicine at Brigham and Women's Hospital, in Boston.
It has long been known that eating fish such as tuna, mackerel, lake trout and salmon, which are
rich in omega-3 fatty acids, is good for the heart. Mozaffarian and his colleagues set out to
discover why.
They analyzed data from more than 5,000 men and women aged 65 and older in the federally funded
cardiovascular Heart Study. The participants were asked whether they ate fish, what kind, and how
often. The researchers compared the answers to those dietary questions with electrocardiogram tests of the study participants.
What they found was that eating fish was associated with a lower heart rate, a slower interval between when the heart received a signal to pump blood and when blood was pumped, and a lower likelihood that the heart would take a long time to reset its electrical system after a beat.
That last effect is important, Mozaffarian said. "The heart resets its electrical activity after every beat," he said. "When there is heart disease, the resetting can be delayed. That is
dangerous."
Animal studies have indicated why the omega-3 fatty oils confer their beneficial effect, Mozaffarian said. "The fish oils get into the membrane of heart cells and affect the function of their protein channels," he said. "Potassium, sodium and calcium pass through those channels, controlling the whole electrical cycle."
While the new study found that the more fish consumed, the greater the benefits, most gains were achieved with just one or two meals of fish a week. That was especially true for the lower heart
rate, Mozaffarian said.
But it had to be the right kind of fish, and prepared the right way. No effect on the heart's
electrical activity was seen with fried fish, such as fish burgers or fish sticks. Those commercial
products do not increase blood levels of omega-3 fatty acids.
And people who think they can take a shortcut by using fish-oil supplements are mistaken, said Alice H. Lichtenstein, professor of public health and family medicine at Tufts University School of
Medicine, and a spokeswoman for the American Heart Association.
"Recent studies have cast doubt on the belief that fish-oil supplements are beneficial," Lichtenstein said.
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