Friday, July 20, 2012

Omega-3s On A Vegan Diet

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:
  1. Which type of omega-3?
  2. How much is "enough?"
The term "omega-3" represents a class of compounds or fatty acids with varying chain lengths and degrees of saturation. Different types perform different functions. Here are three omega-3s (n-3s):

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.
If we would benefit from consuming EPA, DHA, and other long-chain omega-3 fatty acids in the range of about a half gram a day, a vegan may need to supplement. Jack Norris RD (who co-authored "Vegan For Life" with Virginia Messina RD) says that vegans should take a DHA supplement of 300mg/day every few days.
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13 comments:

Bix said...

Norris says DHA supplements can be vegan sourced - from algae.

Bix said...

I actually tried one of these, a product by a company called DEVA. Fresh out of the bottle it tasted fishy.

caulfieldkid said...

Would that suggest that it was/was going rancid, and if so how does that affect it's effectiveness?

shaun

Dr. Mel said...

Thanks for this post Bix--"just what the doctor ordered," ha ha.

Anonymous said...

Great blog!!

If seaweed was the source of the DHA, it would taste "fishy" and not necessarily be rancid, but the omega 3s do need to be kept in a cool dark place.

There are several oils newly identified as good omega 3 sources with lower omega 6s: sacha inchi, argan, echium, etc.

However, one needs to look more at omega 3:6 ratio in the diet rather than just ramping up the omega 3s.

The Standard American Diet (SAD) is sadly too high in omega 6s, which (excepting GLA) increases inflamatory response that predisposes one to inflammatory diseases such as arthritis, CVA & diabetes, while decreasing omega 3 effectiveness etc).

So do not waste money on the omega 3-6-9 supplements. I cannot understand why they are even produced.

Janet

Anonymous said...

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

RB said...

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?

Bix said...

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.

Bix said...

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.

Bix said...

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.

Laurie Endicott Thomas said...

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

Bix said...

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

Dr. Mel said...

I'm looking forward to your post on the omega-6:omega-3 ratio.