by Craig Weatherby
Omega-3 fatty acids come in two distinctly different forms, which differ greatly in their essentiality to human health… and in their clinically demonstrated ability to enhance it.
These two kinds of omega-3s occur in two different groups of foods.
A short-chain omega-3 called ALA is found in leafy green veggies such as spinach, and more abundantly in walnuts, flaxseed, and canola oil.
The two long-chain “marine” omega-3s (EPA and DHA) needed in our cells are unique to oceanic and fresh-water foods such as fish, shellfish, and algae… and to eggs from hens fed DHA-rich fish meal.
The human body needs EPA and DHA for essential cell, brain, immune-system, and metabolic functions.
This is why the FDA-approved heart-health claim for omega-3s applies only to foods or supplements that contain EPA and DHA—or DHA only, which the body can easily convert to EPA as needed—extracted from fish or algae.
And when the FDA began allowing makers of infant formula to add omega-3s, this permission applied only to omega-3 DHA.
The omega-3 conversion issue, explained
Small clinical studies have suggested that humans can only convert very small percentages of omega-3 ALA from plant foods into the omega-3 EPA and DHA required for life and good health.
Accordingly, researchers and public health authorities agree that it’s smarter to ensure adequate blood levels of essential EPA and DHA by getting them directly from dietary fish and/or fish oil.
But there’s always been a bit of disconnect between the clinical findings and the fact that many highly intelligent and accomplished people grew up on and consume adult diets lacking or very low in fish or fish oil.
Two years, we noticed a British study that seemed to suggest that people’s bodies can adapt to low or no intake of fish fats by increasing the rate at which they convert plant-form omega-3 ALA into EPA and DHA (Welch AA et al. 2008).
Now, the same UK team has published a larger follow up study that seems to confirm suspicions that the human body can make much more EPA and DHA from plant foods and meats than thought.
In fact, the researchers found less difference than expected in the EPA-DHA levels in people’s blood, despite large differences in their intakes of omega-3s.
Some important caveats apply to the new findings
The authors failed to mention three important points that give omega-3 EPA and DHA from fish an advantage not reflected in the higher-than-expected blood levels seen in non-fish-eaters.
First, American diets are extremely overloaded with omega-6 fats from common, cheap vegetable oils (corn, soy, safflower, sunflower, cottonseed, etc.) …which compete with omega-3s for absorption into our cells, and promote inflammation when consumed in excess.
People who don’t eat fish or take fish oil can make reasonable amounts of EPA and DHA from omega-3 ALA... if they consume enough leafy greens, walnuts, flaxseed, and canola oil.
However—unless they also cut back on intake of omega-6 fats drastically—it’s much easier for vegetarians and other non-fish eaters to maintain a healthful ratio of omega-3s to omega-6s in their cells by consuming ample amounts of omega-3 EPA and DHA from fatty fish and fish oil.
Second, it is not clear that the “small” differences they observed wouldn’t be significant to people’s health status over a decade or more.
Third, they chose a blood level measure—micromoles per liter—that has not been well-studied as a measure of adequacy.
Instead, virtually all clinical researchers use the percent of omega-3s in red blood cell membranes (the “omega-3 index”) when they’re looking for links between omega-3 levels and heart health.
Thus, the meaning of someone’s micromoles of omega-3s per liter of blood is unclear when it comes to predicting people’s risk of developing heart disease.
What the UK study showed
The new findings come from a research group led by Ailsa Welch at Britain’s University of East Anglia (Welch AA et al. 2010).
There have been many small, careful metabolic studies designed to determine the extent of conversion of dietary ALA to EPA ad DHA.
But this seems to be the first large population study to compare intakes of the various omega-3s (ALA or EPA+DHA) among people with starkly different eating habits to their actual omega-3 EPA+DHA blood levels.
The study included 14,422 men and women aged between 39 and 78 participating in the “EPIC-Norfolk cohort” cancer-risk study, with blood levels of fatty acids being measured in 4,902 of these people.
Despite having significantly lower intakes of EPA and DHA (from fish or fish oil), blood levels of EPA and DHA in vegans and vegetarians were approximately the same as regular fish eaters.
The results indicate that the bodies of vegetarians and other non-fish-eaters can respond to a lack of dietary omega-3 EPA and DHA by increasing their ability to make them from omega-3 ALA.
And as they said, “The implications of this study are that, if conversion of plant-based sources of n-3 PUFAs were … sufficient to maintain health, it could have significant consequences for public health…” (Welch AA et al. 2010).
We would note that that’s a pretty big “if”.
Dr. Welch and her co-workers estimated the intakes of omega-3 ALA, EPA, and DHA among the participating people—fish-eaters and non-fish-eating meat-eaters, vegetarians, or vegans—and compared those intakes with their actual blood levels of ALA, EPA, and DHA.
Their results showed that omega-3 intakes were between 57 and 80 percent lower in the non-fish-eaters, compared with fish-eaters.
However, the differences in blood levels of DHA and EPA between fish eaters and non-fish-eaters were much smaller than those widely divergent intake levels would predict.
The average EPA level in fish eaters was 64.7 micromoles per liter, compared with 57.1, 55.1, and 50 micromoles per liter for non-fish-eating meat-eaters, vegetarians, or vegans, respectively.
Meanwhile, the average DHA level in fish eaters was 271 micromoles per liter, compared with 241.3, 223.5, and 286.4 micromoles per liter for non-fish-eating meat-eaters, vegetarians, or vegans, respectively.
While this study supports past research showing greater conversion of ALA to EPA+DHA in women versus men, and higher conversion rates in non-fish eaters compared to fish eaters, our three caveats remain:
The importance of omega-6 intake.
The unusual blood measure used.
The uncertain clinical significance of the seemingly small but possibly quite significant omega-3 blood-level differences seen between fish eaters and non-fish-eaters.
Clearly, much more research is needed to expand our understanding of the factors that influence conversion of dietary omega-3 ALA from plant foods to the omega-3 DHA and EPA our bodies actually need… and can get far more efficiently from fish and fish oil.
Brenna JT et al. alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans. Prostaglandins Leukot Essent Fatty Acids. 2009 Feb-Mar;80(2-3):85-91. Epub 2009 Mar 9. Review.
Burdge GC et al. Metabolism of alpha-linolenic acid in humans. Prostaglandins Leukot. Essent. Fatty Acids. (2006) 75, 161-168.
Burdge GC. Alpha-linolenic acid metabolism in men and women: nutritional and biological implications. Curr Opin Clin Nutr Metab Care. 2004 Mar;7(2):137-44. Review
Welch AA et al. Dietary fish intake and plasma phospholipid n-3 polyunsaturated fatty acid concentrations in men and women in the European Prospective Investigation into Cancer-Norfolk United Kingdom cohort. Am J Clin Nutr. 2006 Dec;84(6):1330-9.
Welch AA, Bingham SA, Khaw KT. Estimated conversion of alpha-linolenic acid to long chain n-3 polyunsaturated fatty acids is greater than expected in non fish-eating vegetarians and non fish-eating meat-eaters than in fish-eaters. J Hum Nutr Diet. 2008 Jul 15;21(4):404.
Welch AA, Shakya-Shrestha S, Lentjes MA, Wareham NJ, Khaw KT. Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the precursor-product ratio of α-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort. Am J Clin Nutr. 2010 Nov;92(5):1040-51. Epub 2010 Sep 22.
Welch, A.A., Bingham, S.A., Ive, J., et al. (2006) Dietary fish intake and plasma phospholipid n-3 polyunsaturated fatty acid concentrations in men and women in the European Prospective Investigation into Cancer-Norfolk United Kingdom cohort. Am. J. Clin. Nutr. 84, 1330-1339.
Welch, A.A., McTaggart, A., Mulligan, A.A., et al. (2001) DINER (Data Into Nutrients for Epidemiological Research) - a new data-entry program for nutritional analysis in the EPIC-Norfolk cohort and the 7-day diary method. Public Health Nutr. 4, 1253-1265.