Epidemiologic studies have consistently shown that a Mediterranean diet protects against coronary heart disease, obesity, type-2 diabetes and cancer. But one recent study entitled Monounsaturated Fatty Acids and Atherosclerosis by Brown et al, attempted to reveal a direct correlation between monounsaturated fat consumption and atherosclerotic plaque development in deficient (apo) B transgenic and Low density lipoprotein receptor (LDLr) mice. Both types of mice are commonly used in cholesterol and atherosclerotic research, to determine plaque formation with the consumption of certain foods. Apolipoprotein E (Apoe) is a plasma (liquid portion of blood) glycoprotein found on the surface of lipid transporting lipoproteins and plays a critical role in the removal of cholesterol and triglycerides from the blood. Low density lipoprotein receptor (LDLr) which was first discovered by Brown and Goldstein who subsequently received the Nobel Prize in medicine for their research, is found on the cells surface for accepting cholesterol containing LDL for incorporation into the cell membrane. Remember, cholesterol is a necessary component of all cell types in the body. LDLr-deficient mice develop medium arterial plaques in 12 weeks on certain high cholesterol diets while Apoe-deficient mice develop arterial plaque in 14 weeks and thus each serve as good biological model for atherogenic promoting foods. So the researchers in the study fed each transgenic mouse a monounsaturated fat that wasn’t derived from extra virgin olive oil, but used oleic enriched safflower oil. They found both types of mice fed monounsaturated oleic acid-enriched safflower oil developed increased very low density lipoproteins (VLDL) and equivalent rates of atherosclerotic plaque formation. This study mentioned another in which Green Monkeys developed atherosclerosis when consuming monounsaturated fatty acids alongside green monkeys fed saturated fats. Researchers in that study discovered that the monkeys fed an atherogenic diet developed coronary artery blockage because enlarged LDL particles were enriched by oleate as seen in the study with transgenic Apoe and LDLr deficient mice. It seems the causative factor in both cases was the accumulation of neutral lipids in the liver which were converted by an enzyme called Acyl-CoA-cholesterol-o-acyltransferase 2 or ACAT2 into cholesterol oleate which is picked up by LDL and carried into the blood stream where it has a tendency to deposit in arterial walls triggering an immune response that leads to atherosclerosis. Researchers in the same study used both transgenic mice that had there ACAT2 gene deleted and after feeding these ACAT2 deficient mice a diet high in monounsaturated fats, discovered no aortic atherosclerosis. Brown and his team concluded that dietary consumption of monounsaturated oleic fatty acids contribute to atherosclerosis by converting into Oleoyl-CoA which is then esterified to cholesterol oleate by the enzyme ACAT2. After conversion to cholesterol oleate by ACAT2, it’s packaged onto very low density lipoproteins (VLDL) and sent into circulation where it contributes to atherosclerosis by being taken up by macrophages that have a tendency to continue to eat cholesterol and lipid fractions until they balloon into foam cells, which is a critical step in atherogenesis.
Brown et al point out that epidemiology can’t define causality by claiming that one single factor like olive oil in the Mediterranean diet protects against atherosclerosis, but researchers must measure disease in a setting controlled for all but the one factor, not any substitutive markers. The authors of this study did concede the limitations of both studies and that olive oil, which they didn’t use, contains cardio-protective bioactive compounds like oleuropein, carotenoids and other anti-atherogenic phytosterols in its nonsaponifiable fractions which may mediate any atherogenic effect from the oleic acid.
I would say this was a poorly designed study that reveals nothing about the health benefits of extra virgin olive oil and its role in protecting the cardiovascular system. The authors admit that extra virgin olive oil provides more than just oleic acid, but cardiovascular protective antioxidants and phytosterols. This particular study is illustrative of how processed foods (oleic acid-enriched-safflower oil) contribute to dis-ease in the body. Extra virgin olive oil is a unique monounsaturated fat that needs to be studied in a similar controlled trial using experimental animal models and not substituted with damaged, enriched processed oil.
Current Atherosclerosis Reports: Monounsaturated Fatty Acids and Atherosclerosis: Opposing Views from Epidemiology and Experimental Animal Models, J. Mark Brown PhD, Gregory L. Shelness, PhD and Lawrence L. Rudel PhD, 2007.
Thanks for Reading - By Tommy Brooks