
There are 3 types of naturally occurring fats classified by the number of double bonds present in their fatty acid side chains: saturated, monounsaturated, and polyunsaturated.
Polyunsaturated fats can be further classified into 2 groups based on the position of the first double bond site: omega-3 fatty acids and omega-6 fatty acids. The most prominent omega-6 fatty acids in the human diet are arachidonic acid (found in animal meat) and linoleic acid (found in vegetable oils, seeds, and nuts), which can be converted into arachidonic acid by a desaturase enzyme . Major dietary sources of omega-3’s are fish containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and nuts, seeds, and vegetable oils containing a-linolenic acid (ALA), which can be converted to EPA and then DHA by the same desaturase enzyme that converts linoleic acid to arachidonic acid.

Omega-3’s are a unique group of polyunsaturated fats that can be found most abundantly in fatty fish, flaxseed, walnuts, soy, and canola oil. The metabolism of omega-3’s from fish (EPA + DHA) and vegetables (ALA) results in the production of the same eicosanoids (thromboxane, leukotrienes, prostaglandins); however, it is unclear as to what extent ALA is metabolized into these eicosanoids and if this metabolism is directly related to its effect on CVD. It does seem clear from the 4 prospective randomized trials outlined above that both fish and plant sources of omega-3’s can favorably impact cardiovascular health. The impact of omega-3’s is most consistently related to the use of fish oil.
Eicosanoids derived from omega-6’s are generally proinflammatory and proaggretory, whereas those derived from omega-3’s are predominantly anti-inflammatory and inhibit platelet aggregation.6 This fundamental difference may account for the cardioprotective effects of omega-3’s.
It is recommended that patients with known CVD consume one serving (200-400 g) of fatty fish
or 1 g/d of fish oil supplement and maintain a healthy diet that is rich in ALA. Patients with a CVD risk equivalent (diabetes, peripheral vascular disease, etc) should consider consumption of a single serving of fatty fish or 1 g/d of fish oil supplement and eat a healthy diet rich in ALA. Fish oil supplements may be particularly helpful in patients with known CVD or CVD risk equivalents and hypertriglyceridemia. For patients without known CVD, a single serving of fatty fish approximately once or twice a week and a diet rich in ALA should be encouraged. It is prudent to avoid fish that contain high levels of mercury as defined by the FDA. These recommendations are in agreement with the American Heart Association’s scientific statement.
Inflammation is a central component in atheroma formation and plaque rupture,11 and studies have linked systemic markers of inflammation to CVD risk.12 A crosssectional study of 727 women in the Nurses Health Study I found dietary intake of omega-3’s to be inversely related to inflammatory markers C-reactive protein, IL-6, E-selectin, soluble intercellular cell adhesion molecule 1, and soluble vascular cell adhesion molecule 1.
In addition to markers of vascular inflammation, omega-3’s may beneficially influence other factors related to CVD risk: ventricular arrhythmias, thrombosis, triglycerides, apolipoprotein B, high-density lipoprotein, adhesion molecule expression in plaque, platelet-derived growth factor, nitric oxide–induced endothelial relaxation, and blood pressure.
Source:
Understanding omega-3’s
Andrew P. DeFilippis, MD,a and Laurence S. Sperling, MD, FACC, FACPb Atlanta, GA