More people around me are deciding to eat vegan. The latest question has been, "Is it possible to get enough Omega 3s on a vegan diet?" The short answer, from my reading, is maybe not.
There are 2 parts to this question:
- Which type of omega-3?
- How much is "enough?"
ALA Alpha-Linolenic acid 18:3, n-3
EPA Eicosapentaenoic acid 20:5, n-3
DHA Docosahexaenoic acid 22:6, n-3
I'll call ALA "short-chain" (18 carbons in the chain) and EPA and DHA "long chain" (20 and 22 carbons in the chains).
Short-Chain
Many plants are good sources of the short-chain omega-3 (ALA), e.g. flax, walnuts, and greens like spinach, romaine, and kale if you eat a lot. (Omega-3s are polyunsaturated fatty acids and so can be found in higher concentrations in fatty plant foods.) Just 7 walnut halves provide about 1.3 grams of ALA.
The Institute of Medicine (IOM) has set an Adequate Intake (AI) for undifferentiated (short- and long-chain n-3s lumped together) n-3 of 1.6g/day/men and 1.1g/day/women.
For differentiated (ALA only): "An AMDR for α-linolenic acid is estimated to be 0.6 to 1.2 percent of energy. The lower boundary of the range meets the AI for α-linolenic acid."
So, 0.6% of a 2000 calorie diet is 12 calories or 1.3 grams, 1.2% of a 2000 calorie diet is 2.7 grams. Those 7 walnut halves (or a couple teaspoons of ground flax) should do it for most people for short-chain n-3. You'll get even more with the rest of the day's food.
Long-Chain
Since animal foods, particularly seafood, are a better source of the longer-chain omega-3s (EPA and DHA) than plant foods, vegans may have difficulty getting enough. But what is enough? The IOM (in 2002) did not set an AI for EPA and DHA. Our body can convert some of the short-chain ALA to the more potent EPA and DHA but it's variable and inefficient. Many things affect the conversion, including age, gender (women convert more than men), health, and other things eaten including possibly the amount of omega-6 fatty acid. (I'll have more to say about this omega-6:omega-3 ratio in an upcoming post.)
This workshop in 1999:
Workshop on the Essentiality of and Recommended Dietary Intakes for Omega-6 and Omega-3 Fatty Acids, Journal of the American College of Nutrition, 1999
Said 0.65 grams of EPA+DHA a day were an adequate intake.
This study:
Is Docosahexaenoic Acid (DHA) Essential? Lessons from DHA Status Regulation, Our Ancient Diet, Epidemiology and Randomized Controlled Trials, Journal Of Nutrition, 2004
Says that DHA is probably essential, meaning we don't convert enough short-chain ALA for health (brain and retina) and we need to eat it directly. (We're better at making EPA from ALA.)
This workshop:
Towards Establishing Dietary Reference Intakes for Eicosapentaenoic and Docosahexaenoic Acids, Journal of Nutrition, 2009
Recommended that the IOM set a DRI for EPA+DHA of about 0.50 grams.
The only plant sources I know of for the longer chain n-3s are:
- Purslane which contains EPA but not DHA (0.01mg/g which is not very much).
- Mustard greens/red leaf lettuce/buttercrunch lettuce which contain DHA but not EPA (but at very low concentrations, 0.001/0.002/0.001 mg/g respectively).
- Seaweeds which can contain very small amounts of EPA and DHA depending on the type.
12 comments:
Norris says DHA supplements can be vegan sourced - from algae.
I actually tried one of these, a product by a company called DEVA. Fresh out of the bottle it tasted fishy.
Would that suggest that it was/was going rancid, and if so how does that affect it's effectiveness?
shaun
Thanks for this post Bix--"just what the doctor ordered," ha ha.
I wanted to comment on the link for the "Workshop on the Essentiality of and Recommended Dietary Intakes for Omega-6 and Omega-3 Fatty Acids"
The article implicated plant sources (corn safflower and soy), which are out of control in packaged foods. I agree with this finding, but they totally left out the high levels of omega 6s in the cows, chickens, pigs, eggs, and milk consumed in the SAD diet.
To avoid the inflammatory diseases that are so prevelent today, we need to avoid agribusiness animal products, packaged foods, and even most plant oils commonly found on the grocery shelves.
Janet
I agree with Janet. Industrial meat consumption (beef, chicken, pork) does not provide the omega-3 and provides too much omega-6. From a practical point of view, what should one eat to get sufficient long and short chain omega-3? Seaweed does not seem option for most of us unless we live in Japan. It seems that flax seed, beans and veggies apparently aren't sufficient. It seems we need fish in our diets. But eat wild fish, because farmed fished is low in omega-3 because it is typically corn fed like other industrial meat. Supplements shouldn't be the answer. How did people manage to get enough nutrients before supplements came along? Is it a fallacy that we can get all the nutrients we need from food?
This stuff didn't pass the sniff test, shaun. I've had fish oil that wasn't as fishy. The expiration date is 01/14.
I've thought about these questions, RB. I suppose people can live a long life with mild deficiencies. They may assert themselves as, say, poor vision or eczema. I wonder if you could improve not just the quantity of life, but the quality of life, by addressing dietary shortfalls ... with food I'm talking about.
The more calories someone eats, the more opportunity to get nutrients.
I'm changing my mind about the omega-6:omega-3 ratio. I'm collecting my thoughts in a post. I don't think anymore that omega-6 fatty acids, by themselves, elevate levels of inflammatory compounds. I mean, it seems plausible, but it's not panning out in studies.
The EPIC study found that vegan women had higher plasma levels of DHA than fish-eating or meat-eating women did.
http://www.ajcn.org/content/92/5/1040/T5.expansion.html
I think we talked about this study, Laurie.
If you'll notice, the standard deviation on that value (women/vegan/DHA) was really large, about 75% of the mean. That kind of spread points to either an error or at least lessens credibility in the finding.
Also:
- Vegan men had the lowest plasma levels of DHA, fish-eating men had the highest.
- Vegan women had the lowest levels of EPA, fish-eating women had the highest.
- Vegetarian women had the lowest levels of DHA, fish-eating women had the 2nd highest after that unusual value you cited.
The following criticism published in the same journal a few months after this study addressed those problems and others such as inability to assume conversion from ALA to long-chain n-3s and imprecise nutrient data:
Lack of evidence for increased α-linolenic acid metabolism in vegetarians, 2011
I'm looking forward to your post on the omega-6:omega-3 ratio.
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