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Thanks for your detailed CME article in the June 2006 issue of Canadian Family
Physician about omega-3 fatty acids.1
Indeed, there seems to be compelling evidence for their use, but I have some concerns
that I hope you will address.
First, there are many vegetarians in Canada—and the world—who would
like to have additional cardiovascular protection. Many are South Asian and could be
genetically predisposed toward cardiovascular disease. In addition to other lifestyle
and diet changes that they must pursue, it seems that omega-3 supplementation would be
beneficial. Would you be able to comment about whether, or do you have evidence that,
alpha-linolenic acid (ALA) can be promoted as a high-quality source of omega-3 fatty
acids that is also effective for disease prevention? Are there any studies? Apparently
ALA must be converted by our bodies into eicosapentaenoic acid and docosahexaenoic acid.
Does this process occur efficiently?
There are also other reasons that ALA should be promoted as a source of omega-3. The
environmental consequences of our current fish diet are incredible. The effect on
Atlantic fisheries alone is a prime example of the devastation. Fish farms are also
terrible for the environment. Imagine, if people increased their fish consumption by
even a small percentage, what the increased cost to the planet would be. Changing the
biosphere in this way is an anathema, and surely it will also affect human health
someday. Some fish are less taxing on the environment to consume than others. If many
people start switching to these fish, however, surely these fish will also be overfished
and the same problems will occur.
The methylmercury content of fish is also of grave concern. Concentrations of
polychlorinated biphenyls and other toxins and metals also build up in the fish.
Pregnant women and young children in particular must be very cautious about the type,
origin, and quantity of fish they consume. Environmental Defense has an excellent
website: http://www.oceansalive.org. Two
excellent webpages to which you can refer patients are http://www.oceansalive.org/eat.cfm?subnav=healthalerts
and http://www.oceansalive.org/eat.cfm?subnav=bestandworst.
Please have a look.
Footnotes
e-mail
References
1.Schwalfenberg G. Omega-3 fatty acids. Their beneficial role in cardiovascular
health. Can Fam Physician. 2006;52:734–740. Erratum in: Can Fam Physician 2006;52:952. [PMC free article] [PubMed] [Google Scholar]
I would like to thank Dr Mehta for his response and I will try to answer a few of his
questions.
Vegans generally have diets lower in alpha-linolenic acid (ALA) (omega-3) than in
linolenic acid (omega-6) and, thus, must wisely choose oils with higher ALA content.
Alpha-linolenic acid is converted to eicosapentaenoic acid (EPA) (6% in some studies
and 25% in others); however, conversion to docosahexaenoic acid (DHA) in the human
body is poor. As well, the conversion is further limited (by as much as 40%) by
excess omega-6 in the diet, which competes for the same enzyme system.
Cardioprotective effects have been demonstrated for ALA; however, the results are
not as robust as for EPA and DHA. Several articles might help you answer this
question.1-3
Regarding toxins in fish and fish oil (and the use of fish and fish oil in the
perinatal period), I would refer you to another article.4
Industry and farming have seen the light, and new sources of DHA and EPA are on the
horizon. Some of these are listed in Table 3 in my article.5 A new and exciting source of DHA and EPA is eggs from flax-fed
chickens, which produce eggs with less cholesterol and more essential fatty acids.
This concept began in Canada at the University of Alberta. This eventually will
result in less stress on rapidly depleting fish stocks.
Footnotes
e-mail
References
1.Harper CR. Flaxseed oil increases the plasma concentrations of
cardioprotective (n-3) fatty acids in humans. J Nutr. 2006;136(1):83–87. doi: 10.1093/jn/136.1.83. [DOI] [PubMed] [Google Scholar]
2.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):159–173. [PubMed] [Google Scholar]
3.Davis BC. Achieving optimal essential fatty acid status in vegetarians:
current knowledge and practical implications. Am J Clin Nutr. 2003;78(3 Suppl):640–646. doi: 10.1093/ajcn/78.3.640S. [DOI] [PubMed] [Google Scholar]
4.Genuis SJ. Time for an oil check: the role of essential omega-3 fatty
acids in maternal and pediatric health. J Perinatol. 2006;26(6):359–365. doi: 10.1038/sj.jp.7211519. [DOI] [PubMed] [Google Scholar]
5.Schwalfenberg G. Omega-3 fatty acids. Their beneficial role in cardiovascular
health. Can Fam Physician. 2006;52:734–740. Erratum in: Can Fam Physician
2006;52:952. [PMC free article] [PubMed] [Google Scholar]
