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.
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. | link
2. Sanders TA, Roshanai F. Platelet phospholipid fatty acid composition and function in vegans compared with age- and sex-matched omnivore controls. Eur J Clin Nutr. 1992 Nov;46(11):823-31. | link