Dietary fats and breast cancer riskBMJ 2013; 347 doi: https://doi.org/10.1136/bmj.f4518 (Published 16 July 2013) Cite this as: BMJ 2013;347:f4518
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This article reports good evidence that omega 3 fatty acids prevent breast cancer. The role of omega 6 fatty acids is also important. These increase the risk of cancer. Omega 6 fatty acids are the main constituent of vegetable oil. This risk is shown in the recovered data from the Sydney Heart reported in the BMJ of 5 February 2013. The evaluation demonstrates that substituting n6 linoleic acid for saturated fat causes an increase in all cause mortality. Heart disease trials that substitute n6 fatty acid containing vegetable oil for saturated fat show increased cancer rates where the trial continues seven or more years. These results occur because n6 fatty acids are incorporated into cell membranes. Because they are polyunsaturated they are easily oxidised, unlike saturated fatty acids which are stable. When oxidised, the cell membrane is damaged and the cell is destroyed. Repeated cell destruction in epithelial membranes results in cancer.
The ideal ratio of n6:n3 fatty acids in the diet is 1:1. In the West it is 20:1. Before industrial processing made it possible to manufacture vegetable oil in the early 20th century, cancer and heart disease were rare. The recent practice of feeding of grains to animals to fatten them up is a problem. Grass fed animals have a balance of omega 3 and 6. Feeding grains to animals particularly in the last 3 months before slaughter removes omega 3 and boosts omega 6. Conjugated linoleic acid (CLA) which protects humans from obesity and cancer is also depleted by grain feeding. Grass fed or grass finished meat can now only be obtained direct from a few specialist farms. Olive oil is another problem. It contains no omega 3 and 10-12% omega 6. The amount of omega 6 may be much higher if rumours are true that most olive oil is mixed with cheap vegetable oil. Incidentally the high proportion of monounsaturated fat in olive oil causes obesity.
The belief that vegetable oils protect against heart disease is wrong. A trial reported in the BMJ of 1965 substituted omega 6 linoleic acid or olive oil for saturated fat. After two years the omega 6 linoleic acid group had most heart attacks despite a lowering of total cholesterol. Olive oil was almost as bad. This is due to oxidation of polyunsaturated fatty acids in LDL particles. The inhabitants of Roseto, Pennsylvania in the 1950s and 60s stood out for their lack of heart disease. They did not eat olive oil. They kept pigs (not fed on grain like modern pigs) in their gardens and ate plenty of lard.
Humans evolved over two million years to eat animals. Animal fat contains the perfect ratio of saturated, monounsaturated and polyunsaturated fat for our metabolisms. If the animal is grass fed the polyunsaturated fat is a healthy mixture of n3 and n6 fatty acids. We should eat fish and grass fed meat. We should cook with lard or beef dripping.
Competing interests: No competing interests
This literature search of the possible protective effects of fish oils on breast cancer omits to mention hormonal status. The presence of HRT or of the contraceptive pill are significant confounders in any study of breast cancer aetiology. Recent data from USA and Canada showed significant reduction in breast cancer on stopping HRT. Young females should not get cancer in the numbers they currently do in developed countries. There is no female mammal that has anything like the prevalence of breast cancer that women from teens to thirties and forties get. Young men have not got a comparable cancer and their cancer incidence begins much later in life. This suggests that young and not so young females are exposed to a carcinogen that neither mammals nor men are exposed to.What is it then that is responsible for the early and inexorible incidence of breast cancer in young women and in older women? Could this be iatrogenic female hormones in the form of HRT and contraceptive pill? Is it not plausible that the discrepancy that Zheng et al noticed between responses in developed western countries compared to asian and other less developed regions to protection by fish oils, is due to different exposures to female hormones be it as HRT or contraception? This elegant study shows a dose response relation to fish oils but it is difficult to interpret in the absence of data showing dose and duration of any extraneous female hormone exposure.
Competing interests: No competing interests