Instead, we have dramatically increased the consumption of omega-6 fatty acids. Although these too are essential in the diet, their excess results in a pro-inflammatory response that lies at the base of a mix of modern degenerative diseases such as arthritis, autoimmunities and heart disease. The natural diet should have a ratio of omega-6 to omega-3 of about 1:1, but today is more like 20 or 30 to 1! See a problem?
For example, fish can contain the toxins methyl mercury and PCBs (polychlorinated biphenyls), both by-products of our industrial age that gravitate into water. These are lipophilic (fat loving) and thus are present in fish oils and then tend to accumulate in our fat depots when consumed. This is a consideration for dieters since the lipophilic toxins in fat stores that are being rapidly melted away can flood the body, potentially creating a toxic shock. (Not an excuse to not lose weight here, just a caution on radical weight loss or repeated yo-yo dieting.)
This is also of particular concern for pregnant and nursing moms since these toxins can transfer to and accumulate in the fetus, increasing the risk of abnormalities, disease and weakness.
Increasing the amount of omega-3s is not easy and requires a purposeful shift in dietary habits. Official dietary agencies are recommending about 0.65g/day of omega-3s (EPA, DHA) for pregnant and lactating women, and about 1g for people with cardiovascular risk. (These are conservative. In the wild we would naturally consume much more.) To obtain the 1g/day level, 210g of canned light tuna in oil would need to be consumed or about 50g of farmed Atlantic Salmon. Fish type is important, with the cold-water species having the highest concentrations of omega-3s.
Other fish such as tilefish, swordfish, shark, king mackerel and tuna steaks increase the risk of mercury exposure. One can estimate that PCB intake parallels fish consumption.
Omega-3 dietary supplements vary widely in omega-3 content, ranging from 50% to 150% of label claims. Supplements can as well contain mercury and PCBs. Omega-3s are very fragile and can easily convert to toxins themselves when exposed to heat, light, air and water so supplements should be chosen carefully and stored properly.
My feeling is the risk from the toxins is less than the risk of not increasing omega-3s in the diet. For example, the concentration of PCBs in supplements ranges from 2% to 43% of recommended safe levels. If fish are eaten as the main source of omega-3s, variety is what will decrease the risk.
The wise course is to follow the Optimal Health Program?, which will help you return to your dietary roots, including, wild-type foods, raw and fresh as much as possible and appropriately designed supplements. Shop for high omega-3 food options and keep your intake of antioxidants high to protect these fragile oils when they are consumed. Supplements should be chosen carefully, be oxidant protected, properly packaged in light - and oxygen-barrier packaging, and kept frozen until consumed.
In the end, omega-3s are not a new scientific discovery. They are just part of the diet we are genetically programmed to eat. If we had not veered from that design in our eating habits, the omega-3 "discovery" would be meaningless. This is yet another lesson that paying attention to our natural design provides the best hope for prevention and optimal health.