An old clinical study has initiated a new discussion about whether polyunsaturated fat is really better for your heart than saturated fat. Replacing saturated fat with polyunsaturated fats high in linoleic acid (corn, safflower, soybean, sunflower, cottonseed oils) was a mainstay of dietary advice to lower cholesterol and prevent cardiovascular disease for many years. Recently, doubts have been raised about whether this really works and if the linoleic acid contents of these oils are as healthy as was once thought.
Dr Christopher Ramsden of the National Institutes of Health and his colleagues obtained unpublished records of a trial that took place between 1968 and 1973 in a nursing home and some state mental hospitals in Minnesota. Patients in these institutions were randomly assigned to have a control diet that was high in saturated fat and low in polyunsaturated fat, or an intervention diet that contained 9% saturated fat and 13% polyunsaturated fat.
What the study showed must have surprised the researchers, because they did not publish all their results. The intervention diet did lower cholesterol, but the study found that there actually was no difference between their groups in deaths from heart disease, strokes or related conditions and no difference in total deaths. They suggested there was a small beneficial effect on younger patients. Dr Ramsden obtained most of the study data, and re-analyzed its findings. Ramsden and coauthors confirmed the lack of any effect of the intervention diet on heart and cardiovascular health or total deaths. They also found that patients aged 65 years or older were actually harmed. Furthermore, those whose cholesterol was lowered the most, were the most likely to die. Ramsden also found that five other clinical studies that substituted linoleic acid for saturated fat found no benefit in either deaths from heart disease or total deaths.
So what does this study mean? Is saturated fat actually good for you? My answer is NO! What this study clearly demonstrates is something that we can easily see in hindsight: consuming lots of linoleic acid is bad for you! While linoleic acid might lower cholesterol, it is an omega-6 fatty acid. Omega-6 fatty acids increase inflammation, especially when they are eaten in the high amounts that have characterized the American diet in recent decades. We know inflammation aggravates cardiac disease and cancer as well. A diet of 13% linoleic acid may lower your cholesterol, but its pro-inflammatory effect could be lethal!
There are many diets being promoted today that advocate going for high levels of saturated fat in your diet. Coconut oil, lard and butter, along with fatty meats like bacon, are all the rage. A new review of 21 studies finds that coconut oil does raise cholesterol, though not as much as butter. A review of 5 cohort studies in breast cancer patients finds that those who ate the most saturated fat were 63% more likely to die of breast cancer than those who ate the least, so we cannot recommend saturated fat for cancer patients. Saturated fat and polyunsaturated fat can both have villainous aspects.
So what’s left to eat? We recommend that our patients lower overall consumption of fats and oils, and replace butter, coconut oil, lard and unhealthy polyunsaturated fats with more healthful fats and oils. Good choices include those rich in monounsaturated fats as well as those containing omega-3 fats, which reduce inflammation. These include high-quality olive oil and canola oil, and high-oleic versions of safflower and sunflower oils as well as several other types of plant, seed and nut oils that can be used for different applications. Much of your fat intake should also come from nuts like almonds and walnuts, flax seeds or fatty omega-3 rich fish. Fats and oils are just a small part of a healthy and balanced plant-based diet. Block Center dietitians can help you with an individualized diet strategy that works for you, tailored to your disease conditions and health goals, as well as your need to eat a satisfying diet.