Anecdotally, many athletes report that daily consumption of linseed oil reduces post-workout soreness and muscle tightness and also seems to lower the risk of developing a respiratory-system infection. Some even go so far as to contend that regular linseed ingestion helps them carry out greater quantities of high-quality training. Can linseed oil really act in such a miraculous way?
Well, there are plausible physiological mechanisms for such benefits, and these mechanisms hinge on something called alpha-linolenic acid (ALA), an essential fatty acid (meaning it is necessary for complete health and must be supplied in the diet) which is found in high concentrations in linseed oil, as well as walnut and canola oils. ALA is an omega-3 fatty acid, and in the human body it can be used to form an important, longer-chain omega-3 fatty acid called eicosapentaenoic acid (EPA). EPA and its omega-3 siblings, docosapentaenoic acid and docosahexaenoic acid (DHA), are also found naturally in fish and fish oils, and they can all be rapidly incorporated into cell membranes, where they can have a profound influence on metabolic events within cells. Basically, these longer-chain omega-3 fatty acids are thought to help control cell-to-cell communication, enzyme function, immune-system operations, and even gene expression.
As you are probably aware, modern European and American diets tend to be fairly low in ALA and the longer-chain omega-3 fats like EPA and fairly high in an 'n-6' fatty acid called linoleic acid, or LA. LA is present in high concentrations in soy, corn, safflower, and sunflower oils, and once ingested it can be readily converted to another n-6 compound called arachidonic acid (AA). If you're a typical 'westerner,' your cell membranes reflect your diet and thus contain high levels of AA and low concentrations of EPA. That information should be of more than esoteric interest because AA is used to produce two key compounds called prostaglandin E2 (PGE2) and leukotriene B4 (LTB4). PGE2 and LTB4 are pro-inflammatory, ie, they tend to promote inflammation in trouble spots throughout the body (for example, in tissues which have become infected by pathogens - or which have been stressed and damaged by exercise). Specifically, PGE2 can cause pain and blood-vessel dilation, and LTB4 can work together with PGE2 to promote vascular leakage and the extravasation of fluid, creating redness, swelling, and discomfort in the affected area. EPA, which you'll recall can be formed from the ALA in linseed oil, is an inhibitor of the conversion of AA to PGE2 and LTB4 and thus can be viewed as a compound which helps to keep inflammation under control. Athletes are naturally interested in ALA (and linseed oil), believing that ingestion of the compound(s) might be an effective way to control post-workout soreness and stiffness and therefore shorten between-workout recovery time.
However, if you're following along closely, you're probably saying, 'Wait a minute! I thought that inflammation was a normal and essential part of the healing process. If we take away inflammation, won't we be interfering with our natural ability to heal?' If those were your questions, that's good thinking! However, bear in mind that what we have on the table now is 'Western inflammation,' ie, the inflammation associated with high n-6 fatty-acid intakes. This is not necessarily the optimal inflammation pattern for humans; in fact, there is good evidence that in our past history we ingested much higher quantities of n-3 fatty acids and thus (probably) had quite different inflammatory responses to various stressors. Thus, pro-n-3 nutritional experts are simply saying that with more n-3 fatty acids in the
diet the inflammatory response would not go away - it would simply be different. It would be less flamboyant, with less redness, stiffness, swelling, and pain, but perhaps equally (or even more) effective at patching up tissues or ridding the body of pathogens.
Speaking of pathogens, some experts believe ALA can also have a positive effect on the immune system, in addition to its toning of the inflammatory response. To examine this possibility, scientists decided to feed laboratory mice a diet supplemented with linseed oil, which contains a high concentration of ALA. Other mice ate normally or else followed diets low in ALA and high in beef tallow, safflower oil, or fish oil. Each of these dietary groups was divided into two sub-groups; one sub-group engaged in intense exercise (swimming until exhaustion) over an eight-week period while the other was sedentary (Benquet, C et al, 'Modulation of Exercise-Induced Immunosuppression by Dietary Polyunsaturated Fatty Acids in Mice,' Journal of Toxicol Environ Health, Vol. 43(2), pp. 225-237, October 1994).
The protective effect of linseed oil
The researchers challenged the immune systems of the mice by exposing them to sheep red blood cells and were able to show that strenuous exercise markedly suppressed the immune-system response to the foreign cells, except in the mice which consumed linseed oil. Thus, it's possible that diets high in linseed oil might preserve at least some aspects of immune-system function during periods of rugged training.
There is also scientific evidence that suggests that increased ALA and EPA intakes can help control inflammatory disease processes in humans. As potentially potent anti-inflammatory agents, it's very possible that ALA and EPA might help athletes recover more quickly after intense or prolonged workouts.
Although the ALA story is a fascinating one, it's important to note that ALA may not even be the main player on the linseed-oil stage. Linseed oil contains another chemical called beta-sitosterol which also appears to have profound physiological properties. Most notably, beta-sitosterol appears to have cholesterol-lowering properties, and it may well play a key role in immune-system function and inflammation, too.
What happened in South Africa
Very recently, researchers at the Department of Medical Microbiology in
Tygerberg, South Africa took a close look at the effects of beta-sitosterol ingestion on ultra-marathon runners. Nine runners were given capsules containing beta-sitosterol and a 'sterolin' called beta-sitosterol glucoside, while eight athletes received placebo pills. After the race, the runners who received active capsules (with beta-sitosterol and beta-sitosterol glucoside) showed less neutrophilia, lymphopenia and leukocytosis, compared to their counterparts who received placebo capsules (Bouic PJ (firstname.lastname@example.org), et al., 'The Effects of B-Sitosterol (BSS) and B-Sitosterol Glucoside (BSSG) Mixture on Selected Immune Parameters of Marathon Runners: Inhibition of Post Marathon Immune Suppression and Inflammation,' International Journal of Sports Medicine, Vol. 20(4), pp. 258-262, May 1999).
The placebo-treated individuals showed significant increases in their total white-blood-cell numbers, as well as in their neutrophil levels after the race, an indication that they were involved in a large-scale inflammatory response, compared to the beta-sitosterol group. In addition, the beta-sitosterol ultra-marathoners increased concentrations of two key lymphocytes - CD3+ and CD4+ cells. In addition, the lucky runners who took in the active capsules significantly decreased their cortisol: DHEAs ratio, suggesting again that they had less of an inflammatory response but also that they were less immune-suppressed during the post-ultra-marathon recovery period.
'These findings justify further investigations into the use of the phytosterols to prevent the subtle immunosuppression associated with excessive physical stress,' concluded the researchers in understated fashion.