The human body can make most of the types of fats it needs from other fats or raw materials. That isn’t the case for omega-3 fatty acids. These are essential fats—the body can’t make them from scratch but must get them from food. Foods high in Omega-3 include fish, vegetable oils, nuts (especially walnuts), flax seeds, flaxseed oil, and leafy vegetables.
A whole book can be written on all studies conducted to the beneficial effects of Omega 3 fatty acids (also called omega-3 fats and n-3 fats) on age related diseases. Three omega 3 fatty acids are known. What makes omega-3 fats special? They are an integral part of cell membranes throughout the body and affect the function of the cell receptors in these membranes. They provide the starting point for making hormones that regulate blood clotting, contraction and relaxation of artery walls, and inflammation. They also bind to receptors in cells that regulate genetic function. Likely due to these effects, omega-3 fats have been shown to help prevent heart disease and stroke, may help control lupus, eczema, and rheumatoid arthritis, and may play protective roles in cancer and other conditions.
Omega-3 fats are a key family of polyunsaturated fats. There are three main omega-3s:
- EPA - Eicosapentaenoic acid (20 carbons and 5 double bonds) and DHA - Docosahexaenoic acid (22 carbons and 6 double bonds) come mainly from fish, so they are sometimes called marine omega-3s.
- ALA - Alpha Linolenic Acid (18 carbons and 3 double bonds) the most common omega-3 fatty acid in most Western diets, is found in vegetable oils and nuts (especially walnuts), flax seeds and flaxseed oil, leafy vegetables, and some animal fat, especially in grass-fed animals. The human body generally uses ALA for energy, and conversion into EPA and DHA is very limited.
The strongest evidence for a beneficial effect of omega-3 fats has to do with heart disease. These fats appear to help the heart beat at a steady clip and not veer into a dangerous or potentially fatal erratic rhythm. (1) Such arrhythmias cause most of the 500,000-plus cardiac deaths that occur each year in the United States. Omega-3 fats also lower blood pressure and heart rate, improve blood vessel function, and, at higher doses, lower triglycerides and may ease inflammation, which plays a role in the development of atherosclerosis. (1)
Several large trials have evaluated the effect of fish or fish oils on heart disease. In the Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto Miocardio (known as the GISSI Prevention Trial), heart attack survivors who took a 1-gram capsule of omega-3 fats every day for three years were less likely to have a repeat heart attack, stroke, or die of sudden death than those who took a placebo. (2) Notably, the risk of sudden cardiac death was reduced by about 50 percent. In the more recent Japan EPA Lipid Intervention Study (JELIS), participants who took EPA plus a cholesterol-lowering statin were less likely to have a major coronary event (sudden cardiac death, fatal or nonfatal heart attack, unstable angina, or a procedure to open or bypass a narrowed or blocked coronary artery) than those who took a statin alone. (3)
Most people in the developed world take in far more of another essential fat—omega-6 fats—than they do omega-3 fats. Some experts have raised the hypothesis that this higher intake of omega-6 fats could pose problems, cardiovascular and otherwise, but this has not been supported by evidence in humans. (4) In the Health Professionals Follow-up Study, for example, the ratio of omega-6 to omega-3 fats wasn’t linked with risk of heart disease because both of these were beneficial. (5) Many other studies and trials in humans also support cardiovascular benefits of omega-6 fats. Although there is no question that many people could benefit from increasing their intake of omega-3 fats, there is evidence that omega-6 fats also positively influence cardiovascular risk factors and reduce heart disease.
Current research suggests that the anti-inflammatory activity of long-chain n−3 fatty acids may translate into clinical effects. For example, there is evidence that rheumatoid arthritis sufferers taking long-chain n−3 fatty acids from sources such as fish have reduced pain compared to those receiving standard medical inflammation inhibitors such as NSAIDs. Fish oils also appear to reduce ADHD-related symptoms in some children. Double blind studies have shown "medium to strong treatment effects of omega 3 fatty acids on symptoms of ADHD".
A number of studies show that reduced intake of omega-3 fatty acids is associated with increased risk of age related cognitive decline or dementia, including Alzheimer's disease. Scientists believe the omega-3 fatty acid DHA is protective against Alzheimer's disease and dementia.
The beneficial effects of omega 3 fatty acids on cancer are low. A 2010 study of 3,081 women suffering from breast cancer was done to research the effects of polyunsaturated fats on breast cancer. It demonstrated that the consumption of high amounts of long chain omega-3 polyunsaturated fats from food produced a 25% reduced risk of additional breast cancer events. These women were also shown to have reduced risk of “all-cause mortality.” Consumption of polyunsaturated fats through fish oil supplements was not shown to decrease risk of recurring breast cancer events. Other studies also did not show beneficial effects of omega 3 fatty acids on cancer risk. Researchers are taking a hard look at a different sort of balance, this one between possible effects of marine and plant omega-3 fats on prostate cancer. Results from the Health Professionals Follow-up Study and others show that men whose diets are rich in EPA and DHA (mainly from fish and seafood) are less likely to develop advanced prostate cancer than those with low intake of EPA and DHA. (6) At the same time, some-but not all-studies show an increase in prostate cancer and advanced prostate cancer among men with high intakes of ALA (mainly from supplements). However, this effect is inconsistent. In the very large Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, for example, there was no link between ALA intake and early, late, or advanced prostate cancer. (7)
1. Leaf A. Prevention of sudden cardiac death by n-3 polyunsaturated fatty acids. J Cardiovasc Med.(Hagerstown). 2007; 8 Suppl 1:S27-29.
2. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto miocardico. Lancet. 1999; 354:447-55.
3. Yokoyama M, Origasa H, Matsuzaki M, et al. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet.2007; 369:1090-98.
4. Willett WC. The role of dietary n-6 fatty acids in the prevention of cardiovascular disease. J Cardiovasc Med. (Hagerstown). 2007; 8 Suppl 1:S42-5.
5. Mozaffarian D, Ascherio A, Hu FB, et al. Interplay between different polyunsaturated fatty acids and risk of coronary heart disease in men. Circulation. 2005; 111:157-64.
6. Leitzmann MF, Stampfer MJ, Michaud DS, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. Am J Clin Nutr. 2004; 80:204-16.
7. Koralek DO, Peters U, Andriole G, et al. A prospective study of dietary alpha-linolenic acid and the risk of prostate cancer (United States). Cancer Causes Control. 2006; 17:783-91.