Human diet has changed rapidly in recent centuries resulting in a reported increased diet of omega−6 in comparison to omega−3.[83] The rapid evolution of human diet away from a 1:1 omega−3 and omega−6 ratio, such as during the Neolithic Agricultural Revolution, has presumably been too fast for humans to have adapted to biological profiles adept at balancing omega−3 and omega−6 ratios of 1:1.[84] This is commonly believed to be the reason why modern diets are correlated with many inflammatory disorders.[83] While omega−3 polyunsaturated fatty acids may be beneficial in preventing heart disease in humans, the level of omega−6 polyunsaturated fatty acids (and, therefore, the ratio) does not matter.[78][85]

Gorjao, R., Verlengia, R., Lima, T. M., Soriano, F. G., Boaventura, M. F., Kanunfre, C. C., Peres, C. M., Sampaio, S. C., Otton, R., Folador, A., Martins, E. F., Curi, T. C., Portiolli, E. P., Newsholme, P., and Curi, R. Effect of docosahexaenoic acid-rich fish oil supplementation on human leukocyte function. Clin Nutr 2006;25(6):923-938. View abstract.

A 2012 study involved children from 6 to 12 years of age with ADHD who were being treated with methylphenidate and standard behavior therapy for more than six months. The parents of these children reported no improvement in behavior and academic learning using these standard treatments. The researchers randomly gave some of the children an omega-3 and omega-6 acid supplementation or a placebo. They found “statistically significant improvement” for the omega group in the following categories: restlessness, aggressiveness, completing work and academic performance. (5)
Heart disease. Eating fish can be effective for keeping people with healthy hearts free of heart disease. People who already have heart disease might also be able to lower their risk of dying from heart disease by eating fish. The picture is less clear for fish oil supplements. For people who already take heart medications such as a "statin" and those who already eat a decent amount of fish, adding on fish oil might not offer any additional benefit.

The U.S. Food and Drug Administration recommends consuming no more than 3 g/day of EPA and DHA combined, including up to 2 g/day from dietary supplements. Higher doses are sometimes used to lower triglycerides, but anyone taking omega-3s for this purpose should be under the care of a healthcare provider because these doses could cause bleeding problems and possibly affect immune function. Any side effects from taking omega-3 supplements in smaller amounts are usually mild. They include an unpleasant taste in the mouth, bad breath, heartburn, nausea, stomach discomfort, diarrhea, headache, and smelly sweat.
Fish oil supplements have been promoted as easy way to protect the heart, ease inflammation, improve mental health, and lengthen life. Such claims are one reason why Americans spend more than $1 billion a year on over-the-counter fish oil. And food companies are adding it to milk, yogurt, cereal, chocolate, cookies, juice, and hundreds of other foods.
Secondary prevention fish oil studies demonstrate a significant reduction in MI. But unfortunately, both the observational and randomized trials were conducted in an era before the widespread use of HMG-CoA reductase inhibitors, and therefore, the incremental benefit is still unknown. Nevertheless, in patients receiving antiplatelet and anticoagulant therapy in addition to fish oil supplementation (even at doses as high as 4 g per day), no serious adverse complications have been reported.
In fact, dietary fat intake has been among the most widely studied dietary risk factors for breast and prostate cancers. Two studies from 2002 explain how omega-3 can protect against breast cancer. BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2) are two tumor suppressor genes that, when functioning normally, help repair DNA damage, a process that also prevents tumor development.

Pumps the Heart: Where to begin? Omega-3s reduce triglycerides, stabilize your heartbeat, make platelets "less sticky" and can even lower blood pressure. The EPA you get with your daily DHA dose helps prevent artery-blocking clots. In the Iowa Nurses Study (and 3 others), 1 ounce of nuts a day decreased the incidence of heart disease between 20 and 60 percent.
Nielsen, G. L., Faarvang, K. L., Thomsen, B. S., Teglbjaerg, K. L., Jensen, L. T., Hansen, T. M., Lervang, H. H., Schmidt, E. B., Dyerberg, J., and Ernst, E. The effects of dietary supplementation with n-3 polyunsaturated fatty acids in patients with rheumatoid arthritis: a randomized, double blind trial. Eur J Clin Invest 1992;22(10):687-691. View abstract.
*Swordfish contains high levels of mercury, as does shark, king mackerel, and tilefish (sometimes called golden bass or golden snapper). Women who are or may become pregnant, nursing mothers, and young children should avoid these high-mercury species of fish, but can eat up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are lower in mercury.
Children require DHA for growth and development, and the brain, CNS and retina rely heavily on the adequate supply of DHA during growth in the womb. Thus women should emphasise DHA in their diets when they become pregnant and continue to take this until they cease breastfeeding. Children continue to need DHA up until the age they start school, so if children under the age of five are taking an omega-3 supplement, it should contain DHA. The exception is for children with developmental problems – where pure EPA or high EPA omega-3 has been shown to be most effective for supporting cognitive function. We would still recommend, where possible, naturally derived sources of omega-3 such as oily fish to support a balanced EPA and DHA intake.
Weak bones (osteoporosis). Research suggests that taking fish oil alone or together with calcium and evening primrose oil slows the rate of bone loss and increases bone density at the thigh bone (femur) and spine in elderly people with osteoporosis. But taking fish oil does not slow bone loss in older people with osteoarthritis in the knee but without weak bones.
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