Olive oil may have a positive impact on blood lipid levels, but some evidence shows that excess amounts in the diet may cause the progression of atherosclerosis.Most people think that olive oil and other high mono-unsaturated fats (MUFAs) would be heart-healthy additions to their diets. If you are using olive oil or any other high MUFA oil in place of butter, margarine, or other fats containing large amounts of saturated fatty acids (SFA) or trans fatty acids (TFA) then most research suggests this would be healthier. However, there are no clinical trials proving a diet high in MUFA will reverse or prevent clogged arteries.Lipid levels do not tell allA diet high in MUFAs does result in favorable changes in blood lipids when it replaces SFA or TFA in the diet. And it is widely assumed that these changes will slow the progression of atherosclerosis in humans because they reduce LDL or “bad” cholesterol, maintain HDL or “good” cholesterol and reduce the ratio of total cholesterol to HDL. It is important to note, however, that while these changes in blood lipids are favorable if you look at the numbers, they do not prove that a diet high in MUFAs prevents or reverses atherosclerotic lesions.A five year study of monkeys comparing the effects of 3 diets high in polyunsaturated fatty acids (PUFA), SFA and MUFA (35% fat) suggests that improved blood lipids with a high MUFA diet does not necessarily mean less atherosclerosis. This study was designed to mimic a previous study in humans that had shown improved blood lipids in humans. Just as in the human study, the monkeys’ LDL dropped dramatically on both the high PUFA and high MUFA diets compared to the high SFA diet. Again like in humans, the HDL fell significantly on the high PUFA diet but rose slightly on the high MUFA compared with the high SFA diet. However, when they examined the monkey’s arteries the researchers found just as much atherosclerosis on the high MUFA diet as the high SFA diet. By contrast, on the high PUFA diet the atherosclerosis progressed significantly less despite a much lower HDL.Clearly then this research on monkeys questions the long held assumption that changes in blood lipids with differing dietary fats allow one to accurately predict the progression or regression of atherosclerosis.A Mediterranean diet does not simply mean more olive oilThe recent Lyon Diet Heart Study, which showed a significant reduction in mortality, was reported in the media as a Mediterranean diet. It was certainly not a high MUFA diet. The MUFA content was only 12.9% of the calories or about the same as what Americans are now currently consuming. The participants ate 50% less cholesterol, more fiber and a lower ratio of Omega 6s to Omega 3s (4.3 versus 18.3) compared with people eating more typical Western diets. The results of this study do not prove that a diet high in olive oil or other MUFA oils would help reduce the risk of heart disease or promote the regression of atherosclerosis. More research is needed to determine what caused the lower CAD death rate on the more Mediterranean-style diet. This study’s authors suggested it may have been stabilization of the heart muscle membranes due to the higher omega 3 to omega 6 ratio but other factors could be involved as well.The bottom lineAdding calories in the form of olive oil or any refined oil to your diet means that you must subtract these extra calories from another source or you will store these calories as fat. Olive oil is calorie dense and nutrient poor. While it does contain phytochemicals with antioxidant properties, you are far better off getting these from fruits and vegetables that are low in calories and rich in fiber, vitamins and minerals. Your best bet for a heart healthy diet to prevent or regress coronary artery disease is to replace most or all of the beef and poultry you eat with beans and a little fish, eat whole grains in place of refined carbohydrates and increase your intake of fruits and vegetables. Avoid excess sugar and fat, including refined oils, and switch to nonfat dairy products. Dr. James J. Kenney, PhD, RD, FACN is the Nutrition Research Specialist for the Pritikin Longevity Centers. He is on the Board of Directors for the National Council for Reliable Health Information and is Board Certified as a Specialist in Human Nutrition by the American Board of Nutrition.