Using flax seed oil liberally
In an attempt to replicate the putative fatty acid profile of Paleolithic diets, some people use flax seed oil as a source of omega-3 fatty acids.
One tablespoon (15 mL) of flax seed oil supplies 1.7 g of omega-6 linoleic acid (LA), and 7.2 g of omega-3 alpha-linolenic acid (ALA).
Research shows that both linoleic and linolenic acid have proinflammatory effects. Fang et al compared the effects of four 18-carbon fatty acids—oleic, linoleic, linolenic, and stearic acids-- on the expression of the proinflammatory genes cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS) in human retinal pigment epithelium (RPE). Stearic acid is the primary saturated fatty acid found in beef fat, oleic is the monounsaturated fat that dominates olive oil and most nut oils, linoleic is the omega-6 polyunsaturated fat found in most seeds including flax, and linolenic is the omega-3 richly supplied by flax and hemp seeds.
Fang et al found that “oleic acid, linoleic acid (LA), or linolenic acid increased the expression of iNOS and COX-2 genes and the production of prostaglandin E(2 )and nitric oxide (NO) in RPE, whereas the saturated fatty acid stearic acid had little effect on these genes.”
According to the USDA, one tablespoon of beef tallow supplies 2.4 g of stearic acid, and only 0.4 g of linoleic acid, and only 0.08 g of linolenic acid. Hence, we can conclude that beef fat has very little inflammatory potential compared to flax oil, and that it is wiser to eat conventional beef fat than to add flax oil to your food—unless you relish the idea of losing your eyesight to macular degeneration.
Nelson et al performed an experiment to determine the effect of flax seed oil supplementation on inflammatory markers in “healthy” men and women who had abdominal obesity but had no chronic disease, took no medications, and did not exercise. The intervention involved increasing linolenic acid to 5% of total energy intake while decreasing other fat intake to keep caloric intake constant. Nelson et al measured interleukin-6, C-reactive protein, serum amyloid A, and tumor necrosis factor-alpha as markers of inflammation before and after the 8 week intervention.
What happened? Nothing. Nelson et al found found no significant changes in the inflammatory factors after eight weeks of flax oil supplementation.
In “Distribution, interconversion, and dose response of n–3 fatty acids in humans,” Arterburn et al report that non-adipose tissues contain only minute quantities of ALA and EPA. In most organs, DHA generally exceeds EPA 5- to 30-fold, and in the brain and retina, by several hundredfold. They further note that adipose tissue contains about one percent ALA but only very small amounts of DHA or EPA.
These facts imply that 1) we have no need for a continuous supply of ALA, 2) ALA readily contributes to adipose, and 3) we do need a contiuous supply of DHA and EPA (neither supplied by flax oil).
Arterburn et al also report that “ALA has the highest rate of oxidation among all unsaturated fatty acids,” about 22% in women and 33% in men. In addition, “Diets high in ALA appear to increase the rate of ALA oxidation, limiting its accumulation in plasma and reducing its conversion rate to EPA and DHA.” These facts imply that the body places a relatively low value on ALA as a structural lipid and that cells use ALA oxidation to limit the amount of ALA in tissues.
Arterburn et al also report that “The fractional conversion of ALA to EPA…varies between 0.3% and 8% in men, and the conversion of ALA to DHA is <4% and often undetectable in males” but it appears more efficient in women: up to 21% is converted to EPA and up to 9% is converted to DHA.
Also check out: Dietary modification of inflammation with lipids.
In sum, dietary ALA, from flax oil, does not contribute significantly to non-adipose tissue levels of n-3 fatty acids, and because we have limited ability to convert it to EPA or DHA, it does not contribute significantly to tissue levels of those n-3s, or to reduction of n-6 (arichidonic acid, ARA) levels in tissues. However, it may contribute to inflammation and to adipose tissue.
No hunter-gatherer tribe ate flax seed oil, but several ate fish or other marine oils. Hence, it seems wise for modern foragers to follow the same example: get your omega-3s from fish oil and limit or avoid flax oil.
But don’t overdo the fish oil either: Dietary supplementation with eicosapentaenoic acid can decrease natural killer cell activity.
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