Early in his career as a patent examiner Albert Einstein had a boss whose credo was "You have to remain critically vigilant". He urged the young Albert to question every premise, challenge conventional wisdom and never accept the truth of something merely because everyone else views it as obvious; resist being credulous. Einstein developed an independence of judgment that allowed him to challenge basic assumptions.

What has me thinking about Einstein is not his theory of relativity, but rather a book I've just read by Carol Tavris and Elliot Aronson called "Mistakes Were Made (but not by me): Why We Justify Foolish Beliefs, Bad Decisions, and Hurtful Acts". Tavris and Aronson propose that a lot of what ails us as a society is based on our inability to admit that we've been wrong. And what I'm leading up to here is that perhaps it's time we admitted that our promotion of high omega-6 vegetable oils might have been a bit over the top. In our valid haste to get trans fats out of the diet, I fear that not enough attention was paid to the possible downside of just what would replace hydrogenated vegetable oils in the myriad of products that used them. The general thinking was that replacing trans fats with saturated fats would merely be a leap out of the fat and into the fire since "everybody knows" that saturated fats lead to heart disease. (I'll present evidence against that notion in another piece). We now know that perception becomes reality irrespective of fact when enough people believe it; or in other words, if we feel it's true, then it is --even if it isn't! Those of you old enough might recall when our advice to all (cardiac patient or not) was to severely limit the intake of the demon egg. Sure enough, we have egg on our collective faces over that one...though nobody seems particularly embarrassed by how wrong we were (nutrition is an evolving science, after all).

So my issue now is not to suggest that animal fats should at least partially replace hydrogenated fats (although I think they should), but instead to dray attention to the real threat posed by excessive intake of the omega-6 fatty acids, especially when that intake further skews an already inappropriate ratio of omega-6:omega-3. The importance of omega-3s in the diet won't be discussed today, since I'm pretty sure that most people are aware of this fact already.

Statistics reveal that the diet of the average person in developed countries contain roughly ten times more vegetable oil than it did fifty years ago. I would go so far as to suggest that we're consuming roughly 1000 times more than we did a century ago. After all, who could squeeze a corn cob? Expressed oil simply wasn't available, although those who lived around the Mediterranean did have olive oil with its relatively low level of linoleic acid. Over fifty years ago it was determined that the necessary requirement for essential fatty acids is fulfilled when 1 to 2 percent of the total daily caloric intake is provided by linoleic acid...a diet of 1800 calories per day should provide 2 to 4 grams of linoleic acid (an omega-6 fatty acid). Current intake of linoleic acid, by many estimates, is in the 19-22 percent range...and going higher. There has been speculation that the effectiveness of statin treatment is due to not only lowering serum fatty acid concentrations, but also to altering the relative percentages of omega-6 and omega-3 fatty acids. It is evident from the research literature that lipid oxidation in vivo can and does occur (with linoleic acid being one of the prime substrates), and that this is detrimental to human health.

Omega-6 and Cancer
Linoleic acid is the only fatty acid to exhibit an unequivocal cancer-enhancing effect in rodents, impacting mammary, pancreatic and colon cancer. A number of nutrients exhibit tumour-enhancing properties, but excessive levels of intake are usually required. This is not the case, however, with linoleic acid of which only five times the amount needed for optimal growth will bring about mammary tumour development in rats. The effect of "fat type: has been the subject of a great deal of research, but the effects are almost always related to linoleic acid intake. The more linoleic acid in a product (corn oil, for example), the more carcinogenesis enhancement compared to low linoleic acid foods like fish oils, dairy fat and beef tallow.

In 1997 D.P. Rose examined the effect of dietary fatty acids on breast and prostate cancer and concluded that "omega-6 fatty acids perform functions in experimental prostate cancer progression similar to those described for breast cancer" and that saturated fats have no effect on breast carcinogenesis or progression. S. L. Goodstine's research indicated that a higher omega-3:omega-6 ratio would reduce the risk of breast cancer, especially in pre-menopausal women. Hilakivi-Clarke looked at the influence of maternal diet on breast cancer risk among female offspring and determined that "a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat-and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats". It's not a great stretch to postulate that the same may be true regarding prostate cancer risk in male offspring of mothers on diets rich in linoleic acid. In fact, writing a commentary in Carcinogenesis, Bartsch was of the opinion that a high intake of PUFAs stimulates several stages in the development of mammary, colon and possibly prostate cancer from an increase in oxidative DNA damage to effects on cell proliferation, free estrogen levels to hormonal catabolism. Results from the EURAMIC (European Community Multicentre Study on Antioxidants, Myocardial Infarction, and Cancer) breast cancer study also provide evidence for the hypothesis that the balance between omega-6 and omega-3 may play a role in breast cancer. Spanish researchers found that an excess of omega-6 fats in the diet accelerates breast cancer by altering the activity of a group of genes.

Looking specifically at prostate cancer Godley researched biomarkers of essential fatty acid consumption and found that "linoleic acid consumption was positively associated with prostate cancer risk, which is consistent with results from animal experiments". Wang investigated the impact of high versus low-fat diet on risk of prostate cancer and found that fat reduction was definitely helpful The reporting of that study, however, generally failed to mention that the source of the fat in the high-fat diet was linoleic acid (0mega-6) rich corn oil. A 2006 study found that a diet rich in omega-6 fatty acids appeared to promote the spread of prostate cancer, while a diet rich in omega-3s impeded the spread. Hughes-Fulford in 2006 found a significant link between the ratio of omega-6:0mega-3 and prostate cancer and was quoted as saying she would never use any of the high-linoleic acid oils. In 2007 Neuhauser and his group found that omega-6 rich oils increase, and dairy foods decrease prostate cancer risk.

Among several conditions laid at the foot of excessive linoleic acid intake are asthma. eczema, allergic rhinitis, and hay fever. Additionally, PUFAs have been associated with weight gain in adults and children. Writing in Obesity Reviews, Ailhud summarized "experimental evidence which supports polyunsaturated fatty acids of the omega-6 series as being potent promoters of both adipogenesis in vitro and adipose tissue development in vivo during the gestation/lactation period. It is proposed that unnoticed changes in fatty acid composition of ingested fats over the last decades have been important determinants in the increasing prevalence of childhood overweight and obesity" And finally, a case-control study Nkondjock gave evidence that substituting polyunsaturated fatty acids with saturated or monounsaturated fatty acids may reduce pancreatic cancer risk.

Thomas Edison once said "The doctor of the future will give no medicine, but will interest his patients in the care of the human body, in diet and in the cause of prevention of disease". Though Edison was no dietitian, I think he was on to something. I also think we must strive to avoid "group think"...the process whereby like-minded people, talking only with one another, usually end up believing a more extreme version of what they thought before they started to talk. One of the reasons for this, according to American researchers David Meyers and G.D. Bishop, is that when people's views are confirmed by others they tend to become more confident and more extreme. Another reason is that most people are loath to come down on the wrong side of an issue on which there seems to be consensus.
Refernces available on request.