Omega-6s: Not So Bad?
For background on the discussion below, please see Omega-3s in Vegetarian Diets.
The July 2012 issue of the Academy of Nutrition and Dietetics (AND) contained a meta-analysis of studies examining the intake of the omega-6 polyunsaturated fat, linoleic acid (LA), and whether it increases markers of inflammation (1). The AND recommends that people get 3-10% of calories as omega-6s, most of which will be in the form of LA. There is concern that large amounts of LA will be converted to arachidonic acid (AA) and will also prevent the conversion of alpha-linolenic acid (ALA) into EPA and DHA, both of which could increase inflammation.
The meta-analysis found no evidence that intakes of LA up to 10% of calories increased markers of inflammation. Adding LA to the diet did reduce levels of EPA in the blood, but this did not increase inflammation. Adding LA to the diet did not decrease the amount of DHA in the blood, but this is probably due to the fact that so little ALA is effectively converted all the way to DHA in the first place.
In a study from 1992 (2), vegans ate 9-10% of their calories as LA and, of course, had no natural dietary source of DHA. Whether large amounts of LA harm the DHA status of vegans has yet to be determined, but this meta-analysis indicates that reducing LA, a recommendation vegan health professionals have long suggested as a way to reduce inflammation and increase the conversion of ALA to DHA, might not be effective. It also provides more evidence that a DHA supplement might be the only reliable way for vegans to increase DHA levels, since reducing (or, actually, “not increasing”) LA intake does not appear to matter.
I have not changed my recommendations to limit LA based on this meta-analysis alone, but I’m leaning in that direction. Hopefully, there will be more research to come.
References
1. Johnson GH, Fritsche K. Effect of Dietary Linoleic Acid on Markers of Inflammation in Healthy Persons: A Systematic Review of Randomized Controlled Trials. Journal of the Academy of Nutrition and Dietetics. 2012 Jul;112(7):1029-41. | linklink
July 14th, 2012 at 9:10 pm
Consistent with this changing view of n-6 fatty acids, see also Fritsche, K.L. Too much linoleic acid promotes inflammation – doesn’t it? Protaglandins,Leukotrienes and Essential Fatty Acids, 2008; 79: 173-175. The possibility that n-6 fatty acids may not be as inflammatory as previously thought seems to fit with the fact that nuts and seeds have typically been found to have anti-inflammatory effects.
July 15th, 2012 at 9:55 am
Jack, do you think there is a problem in eating tahini daily?
July 15th, 2012 at 7:29 pm
Daniel,
No, I don’t.
July 16th, 2012 at 1:57 am
Agree with you Jack and Kate. Fritche et al., what Kate refers to, is another robust evidence that LA intake is not converted into AA.
May 22nd, 2013 at 1:58 am
“Hopefully, there will be more research to come.”
However, while COX-1 and COX-2 are both located in the blood vessels, stomach and the kidneys, prostaglandin levels are increased by COX-2 in scenarios of inflammation. – http://en.wikipedia.org/wiki/Prostaglandin#Cyclooxygenases
http://www.atsjournals.org/doi/abs/10.1165/rcmb.2008-0105OC
http://tpx.sagepub.com/content/32/6/650
http://www.ncbi.nlm.nih.gov/pubmed/15695412
http://ajplung.physiology.org/content/297/5/L892
http://ajplung.physiology.org/content/287/5/L981
I am sure there is more exogenous toxins which cause the increase expression of COX-2 enzyme, as only natural.
Based on the science, it seems that the Omega 6’s are best limited by those living in polluted cities, those who smoke and those who inhale or ingest toxins.