Dietary recommendations regarding fat consumption are by no means a settled matter. Scientists are still debating this complex topic, and some may disagree on how much fat and which types of fat are most likely to ensure a healthy heart and brain. Instead of trying to untangle the latest research, concentrating on eating a healthy diet overall may be the best bet for your brain, an MGH expert suggests.
“The most important thing is the big picture,” says MGH neurologist Marie Pasinski, MD. “We have to look at the best studies that follow large groups of people over time. In these studies there’s no doubt that the Mediterranean diet—which encourages the consumption of healthy monounsaturated and polyunsaturated fats found in nuts, fish, olive and canola oils, while discouraging unhealthy saturated fats and trans fats—comes out ahead in many factors that positively affect the brain.”
A contributor to recent discussions regarding dietary fat was a study published in the Feb. 5, 2013 issue of the journal BMJ. This research suggested that polyunsaturated vegetable oils that contain high percentages of linoleic acid (such as safflower oil, sunflower oil, corn oil, and soybean oil) might be worse for cardiovascular health than saturated fats (fats found in animal products such as butter, cheese, and fatty meats). The research findings challenged well-established guidelines on fat consumption promulgated by the American Heart Association (AHA), which encourage the consumption of cholesterol-lowering polyunsaturated fats to avoid the dangers of saturated fats, which are thought to boost levels of “bad” blood-vessel-clogging LDL cholesterol.
The BMJ research involved an analysis of unpublished data from a 1966-1973 heart study of 458 men with a history of heart disease. Half of the participants consumed a normal diet with saturated fats, and half were told to restrict saturated fats and replace them with safflower oil, an omega-6 polyunsaturated fat. The researchers found that over three years, the safflower oil group experienced a higher risk of death from heart disease, and from all causes overall, than the other group. The researchers theorized that although they have beneficial effects on cholesterol levels, polyunsaturated fats with linoleic acid may also promote negative factors associated with higher heart-attack risk, such as inflammation, oxidation, or clotting.
“This study is interesting, but alone it doesn’t change the prevailing view that saturated fats are not good for the heart or the brain,” says Dr. Pasinski. “It is a relatively small study involving only men who previously had a coronary event. Moreover, the researchers did not provide information about the consumption of healthy monounsaturated fats, such as olive or canola oil, or of unhealthy trans fats—hydrogenated fats made by chemically altering the structure of vegetable oil to add solidity, which are known to raise levels of LDL cholesterol and lower levels of ‘good’ HDL cholesterol. The study also refutes a large body of research that has demonstrated the cardiovascular benefits of linoleic acid.”
To add to the confusion, other recent research has included studies that call into question the benefits of low-fat diets, which typically restrict or eliminate healthy fats and replace fat calories with sugars and carboyhydrates, and linked low dietary levels of saturated fats with improved clearance from the brain of a hallmark of Alzheimer’s disease (AD), toxic beta-amyloid protein. (See page 5.)
Rather than trying to make sense of sometimes conflicting data on dietary fats, it might be more productive to focus instead on a whole-diet approach, Dr. Pasinski suggests.
“An impressive body of research suggests that people who consume a Mediterranean-style diet experience lower risk for AD and stroke,” she says. “A study published in February 2014 in the online journal PLoS One found that among a large group of firefighters, those who adhered to a Mediterranean-style diet were 35 percent less likely than those who ate a normal American diet to develop metabolic syndrome—a constellation of factors that negatively affect the heart and brain, including obesity, high blood pressure, unhealthy blood sugar levels and unfavorable lipid profiles.
“Olive oil, an essential component of the Mediterranean-style diet, has been associated with better cognitive performance and lower stroke rates.”
Dr. Pasinski, a Harvard neurologist and author of the bestselling book on brain health, Beautiful Brain, Beautiful You, points out that fat may not be the only factor that explains the positive effects of the Mediterranean diet. Beneficial foods such as whole grains, vegetables, legumes and fruit are the mainstay of every meal. Fish, seafood, and nuts are dietary staples, while poultry and eggs are served less frequently. Small amounts of wine are typically taken with meals.
This healthy eating plan contains abundant amounts of antioxidants and micronutrients that benefit the heart and brain. The diet is also low in red meats, dairy products, and sweets—regular consumption of which has been linked to health problems. The Mediterranean-style diet’s well-balanced variety of basic nutrients promotes healthy blood vessels and helps brain cells renew themselves and resist disease and metabolic changes that may come with aging.
A balance of fats
The chemical structure of fatty acids contained in fats and oils, and the balance of fats an individual consumes, strongly impact brain health. Too much unhealthy fat can harm the brain by clogging blood vessels with waxy cholesterol plaque, impairing communication among cells, negatively influencing mood, and discouraging the formation of nerve connections important to learning, concentration and memory. Beneficial fats, on the other hand, are essential cerebral building blocks. They make up brain structures, including the myelin sheaths that coat nerve fibers and neuronal membranes.
Generally speaking, fats that worsen blood cholesterol levels are considered unhealthy, and those that improve them are considered healthy. Fats that should be restricted or eliminated from the diet are trans fats and saturated fats that are solid at room temperature. Brain-healthy fats, or unsaturated fats, are derived from plant sources such as nuts, seeds and vegetable oils, and from fish. Consuming these fats may help lower levels of LDL and increase levels of HDL, resulting in healthier blood vessels.