Re: Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis
Congratulations to Christopher Ramsden et al on producing a study which will hopefully bring some positive changes to more than cardiovascular health alone. (1)
The modern diet has overemphasised the need to consume polyunsaturated fats in the belief that they were a healthy choice, particularly in cholesterol management. They have in fact caused cyclo-oxygenase-2 (cox-2) overexpression and therefore inflammation. Is cholesterol, which is vital for good health, the real villain in cardiovascular health? A recent article published in the BMJ (2) advised the public against consuming too many eggs as they contained cholesterol. If they didn’t there would be no egg, and indeed no chicken – quite a conundrum! Generations have been persuaded by the food and drug industry that ‘functional foods’ such as margarines fortified with EFAs will give us good health, have we been duped?
The biological mechanisms (delta 5 and delta 6 desaturases) required for the uptake of essential fatty acids such as omega 3 and 6 are impaired in those with diabetes (particularly type 2 diabetes (T2DM), a population group at high risk of cardiovascular disease).
The successful absorption of EFAs also relies on adequate levels of certain vitamins and minerals. The poor absorption of EFAs is further confounded by consuming a high carbohydrate diet such as recommended to those with T2DM.
Over nutrition triggers the onset of oxidative stress in the liver due to higher availability and oxidation of fatty acids, with development of hyperinsulinemia and insulin resistance, and omega 3 long-chain polyunsaturated FA depletion, with enhancement in the omegas 6/3 LCPUFA ratio favouring a pro-inflammatory state. (3)
Commercial food processing destroys a significant amount of EFAs, along with their oxygenating ability.
Consumption of good quality omega 6 and 3 EFAs is a haphazard affair. Polyunsaturated oils are unstable and very quickly become rancid. Oxidized fatty acids are dangerous to our health. Lipid peroxidation and oxidative stress are important factors in this damage. (4)
Further damage is also caused by heating polyunsaturated fats in cooking (particularly frying foods).
Many omega 3 research trials did not consider the omega 3/6 essential fatty acid ratio which is vital to the eicossanoid balance. The correct omega 3/6 ratio is fundamental to holistic health for all. I believe that with simple dietary intervention diabetes complications such as retinopathy and nephropathy, could be ameliorated or prevented. Of real concern is the epidemic of T2DM in young people encompassing those of reproductive age. Healthy fertility and reproduction fundamentally rely on good nutrition, including EFAs in plentiful supply. Poor maternal health is a cause for concern and may predict poor health in the next generations.
As the study authors suggest their findings may have important implications for worldwide dietary advice. In this context it would be helpful to look at different aspects of the trial not just dietary fats. The study may reflect the benefits of the Australian lifestyle, level of exercise, vitamin and mineral status, quality of meat (including the quality and method of animal feeding/farming), quality of fats and oils, fish consumption, consumption of processed/fried foods and carbohydrate intake. The study of fats and lipids is a highly complex matter warranting a holistic approach. I hope further studies on this subject can also be aimed at primary prevention of disease with potentially promising results.
(1) Christopher E Ramsden, Daisy Zamora, Boonseng Leelarthaepin, Sharon F Majchrzak-Hong, Keturah R Faurot, Chirayath M Suchindran, Amit Ringel, John M Davis, Joseph R Hibbeln, Use o f dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ 2013;346:e8707
(2) Ying Rong, Li Chen, Tingting Zhu, Yadong Song, Miao Yu, Zhilei Shan, Amanda Sands, Frank B Hu, Liegang Liu, Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies. BMJ 2013;346:e8539
(3) Valenzuela R, Videla LA.The importance of the long-chain polyunsaturated fatty acid n-6/n-3 ratio in development of non-alcoholic fatty liver associated with obesity. Food Funct. 2011 Nov;2(11):644-8. doi: 10.1039/c1fo10133a. Epub 2011 Oct 19.
(4) Moore, K., and L. J. Roberts 2nd. 1998. Measurement of lipid peroxidation. Free Radic. Res. 28: 659–671
Competing interests: No competing interests