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Two large research reviews by medical scientists have determined that omega-3 fatty acids from plants reduce the incidence of heart disease and heart attacks while fish oil has only a slight ("insignificant") effect.
The most recent study focusing on the omega-3 fatty acid alpha-linolenic acid (ALA) comes from researchers at Harvard Medical School along with several other prestigious universities. The researchers analyzed 27 clinical trials that studied 251,049 human subjects. The studies included over 15,000 heart attacks and other cardiovascular events.
The cardiovascular events were cross-referenced against either supplementation or blood levels of ALA. In total, increased consumption of alpha-linolenic acid omega-3 fatty acids resulted in a 14% total reduction of heart attacks and associated cardiovascular events. And as trends were pooled and examined with ALA blood biomarkers, the reduction in cardiovascular events was as high as 20%.
These results are contrasted with another large review of research, published in September's Journal of the American Medical Association. The research comes from medical researchers from Greece's Ioannina University Medical School and Hospital. In this study, researchers utilized the Cochrane Central Register of Controlled Trials of research for fish oil and cardiovascular events research through August of 2012.
The researchers analyzed 20 studies involving 68,680 human subjects. Among these, there were 3,993 deaths from heart attacks and cardiovascular events, 1,150 sudden deaths, 1,837 heart attacks and 1,490 strokes. Against these were cross-referenced marine-sourced (fish) omega-3 fatty acids, which include DHA and EPA, along with saturated fats (yes, fish oil typically contains saturated fats).
The research found that fish oil supplementation did slightly reduce the incidence of heart attacks by 11% and heart attack deaths by 9%. However, given the scale of the margin of error, the researchers concluded that fish oil supplementation, "was not associated with a lower risk of all-cause mortality, cardiac death, sudden death, myocardial infarction, or stroke based on relative and absolute measures of association." In other words, there wasn't enough of a difference from the margin of error to claim fish oil reduces heart attacks or cardiovascular events.
Supporting the conflicting evidence, the researchers also stated:
"Treatment with marine-derived omega-3 polyunsaturated fatty acids (PUFAs) for the prevention of major cardiovascular adverse outcomes has been supported by a number of randomized clinical trials (RCTs) and refuted by others."
The research on plant-based alpha-linolenic acid omega-3s has not been so controversial because research over the years has consistently shown ALA's ability to help prevent cardiovascular events and cardiovascular disease. And this is illustrated with the size of the study analysis (totaling 251,049 humans).
Alpha-linolenic acid is one of the primary fatty acids found in various seeds, nuts and grains. Some of the highest levels are found in chia seeds (64%), kiwi fruit seeds (62%), flax seeds (55%) and hemp seeds (20%). Other good sources include walnuts, pumpkin seeds, sesame seeds, olives, canola, kale, spirulina, spinach and others.
In addition to being well utilized by the body, alpha-linolenic acid (ALA) is also converted to docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and other important omega-3s within the body. The primary liver enzyme used in the conversion of ALA to DHA is delta-6 desaturase. DHA converts to EPA in the body as needed. A healthy person will convert ALA to DHA at a rate of from 7% to 15% according to research.
For those who convert ALA to DHA at a slower rate, algal DHA provides the purest form of DHA. DHA is produced by algae and travels up the sealife food chain. Algal DHA does not contain saturated fats as many fish do. DHA-producing algae is farmed in tanks in the absence of mercury, PCBs and dioxins that have been known to bioaccumulate within fish.
DHA and EPA are the central fatty acids in fish oil besides saturated fat. It also should be noted that fatty fish such as salmon also contain a considerable amount of arachidonic acid. Foods rich in arachidonic acids have been shown to increase inflammation in the body.
Pan A, Chen M, Chowdhury R, Wu JH, Sun Q, Campos H, Mozaffarian D, Hu FB. α-Linolenic acid and risk of cardiovascular disease: a systematic review and meta-analysis. Am J Clin Nutr. 2012 Oct 17.
Rizos EC, Ntzani EE, Bika E, Kostapanos MS, Elisaf MS. Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: a systematic review and meta-analysis. JAMA. 2012 Sep 12;308(10):1024-33.
Adams C. The Living Food Diet: The Ultimate Diet for Increasing Vitality, Losing Weight and Preventing Disease. Logical Bks, 2012.