Omega-3 Fatty Acids in Seafood
By G. Douglas Andersen, DC, DACBSP, CCN
In my practice, I have noticed a growing number of patients who are aware that omega-3 fatty acids are beneficial for their hearts. Many have been advised to consume more omega-3 fatty acids.
Unfortunately, few know which types of food, other than salmon, are the best sources. My vegetarian patients are always surprised to hear that vegetable sources of omega-3 fatty acids (alpha-linolenic acid, aka ALA) are poorly converted to their bioactive cousins, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In optimal conditions, humans convert no more than 15 percent of ALA to EPA/DHA.1
Age, obesity, genetics and the typical Western diet reduce this conversion, which is predominantly to EPA. ALA to DHA conversion is under 4 percent.2
Vegetable Sources of Omega-3
Fatty Acids as Alpha-Linolenic Acid (ALA)
*Using an average of 10 percent conversion ability.
|Source (1 Tbsp) ||ALA ||EPA/DHA* |
|Flaxseed oil ||7,000 mg ||160 mg |
|Canola oil ||1,600 mg ||160 mg |
|Walnut oil ||1,400 mg ||140 mg |
|Soy oil ||1,000 mg ||100 mg |
|Flax seeds ||2,000 mg ||200 mg |
|Walnuts ||600 mg ||60 mg |
While the cardioprotective effects (especially EPA) of omega-3 fatty acids garner most of the press, there is growing evidence that they enhance brain function (especially DHA) from birth to death.3,4,5,6 Mozaffarian and Rimm reviewed numerous trials and concluded that omega-3 intake of at least 250 mg/day for low-risk groups and 500-1,000 mg/day for higher risk individuals reduces overall mortality by 17 percent, and death from heart problems by 36 percent.7
The perfect food for hearts and minds does have a downside. In the past few years, researchers have begun to take note of rising levels of mercury, polychlorinated biphenyls (PCBs), and dioxins. In my next article, I will address the topic of chemical contamination in seafood in greater detail. The general consensus is that the lives lengthened by the reduction of heart disease in people who consume omega-3 fatty acids from seafood is much greater than the lives lost from cancer caused by high levels of contamination in food from the sea.
- Kris-Etherton PM, Harris WF, Appel LJ. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. AHA scientific statement. Circulation, 2002;106:2747-57.
- Gerster H. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? Int J Vitam Nutr Res, 1998;68(3):159-73.
- Olsen SF, Osterdal Ml, et al. Duration of pregnancy in relation to seafood intake during early and mid pregnancy: a prospective cohort. Eur J Epidemiol, 2006;21(10):749-58.
- Nemets H, Nemets B, et al. Omega-3 treatment of childhood depression: a controlled double-blind pilot study. Am J Psychiatry, 2006;163(6):1098-1100.
- Dunstan JA, Simmer K, et al. Cognitive assessment at 2.5 years following fish oil supplementation in pregnancy: a randomized controlled trial. Arch Dis Child and Fetal Neonatal Ed. Preprint Epub. 12/21/06.
Omega-3 Levels in Seafood7,8
*USDA serving size tends to vary. In this table, the numbers are calculated based on 3.5 ounces (100 grams). This is not a uniform serving size; for example, a serving of sardines is only 2 ounces, while a serving of salmon is 6 ounces (according to the U.S. Department of Agriculture).
|Seafood ||EPA/DHA** |
|Anchovies ||2,050 mg |
|Golden Bass |
Gulf of Mexico
|900 mg |
|Blackfish ||400 mg |
|200 mg |
|Clams ||300 mg |
|300 mg |
|400 mg |
|Halibut ||500 mg |
|2,000 mg |
|Lobster ||100 mg |
|1,200 mg |
|Mahi Mahi ||150 mg |
|Mussels ||800 mg |
|700 mg |
|Pollock (Alaskan) ||450 mg |
|Rockfish ||400 mg |
|Salmon (canned) |
|1,400 mg |
|Sardines ||1,000 mg |
|Scallops ||350 mg |
|Shark ||700 mg |
|Shrimp ||300 mg |
|Snapper ||300 mg |
|Sole ||500 mg |
|Swordfish ||800 mg |
|Trout (Rainbow) |
|1,100 mg |
|850 mg |
**Rounded to the nearest 50 mg. The levels of omega-3 fatty acids in seafood can vary by up to 300 percent. This is due to the type of food the fish consume, along with the location, age and season they are caught. Human influences, including processing, storage, packaging and cooking, can also affect the amount of omega-3 fatty acids in a given serving of fish.
- Freund-Levi Y, Eriksdotter-Johangen M, et al. Omega-3 fatty acid treatment in 174 patients with mild to moderate Alzheimer's disease: the OmegaAD study: a randomized double-blind trial. Arch Neurol, 2006;63(10):1402-8.
- Mozaffarian D, Rimm EB. Fish intake, contaminants and human health: evaluating the risks and benefits. JAMA, 2006;296(15):1885-99.
- Information available here.
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