June 30, 2010
The dietary teaching of the 1990s warned Americans to avoid fats at all costs. This energy-dense stuff would cause fatness, artery clogging, and myriad other harmful health effects. Terrified, dieters turned to all the “low fat” products they could find. Eager to capitalize on the craze, food manufacturers cut the fat (and loaded up on the sugar) to offer an abundance of highly-processed “fat free” crackers, cookies, chips, breads, and ice creams. Dieters consumed these products en masse, but yet Americans continued to get fatter. Meanwhile, across the Atlantic in the countries bordering the Mediterranean Sea, the healthiest eaters in the world continued to relish olive oil, fatty fish, nuts, and other very healthy, high-fat foods. Now well-established as the most heart healthy way of eating, the Mediterranean diet is based on an eating plan which contains significantly more calories from fat (about 35-40% of calories) than what the American Heart Association has historically recommended (<30%). However, as research demonstrating the beneficial effects of the Mediterranean Diet accumulates, the dietary teaching in the United States is changing gears.
It turns out that not all fat is “bad.” While it is true that fat contains 225% more calories per gram than protein and carbohydrates (9 calories per gram for fat versus 4 calories/gram for protein and carbohydrate) and thus it must be consumed in moderation for weight control, certain fats possess extraordinary health benefits. Others however deserve their bad reputation for promoting heart disease, obesity, and poor health.
In general, unsaturated fatty acids are the more heart-healthy fats. Unsaturated fats contain one (“monounsaturated” or more (“polyunsaturated”) double bonds between carbon atoms, are typically liquid at room temperature, and are fairly unstable, making them susceptible to oxidative damage and a shortened shelf life. The most heart healthy of the unsaturated fats are monounsaturated fats and a certain type of polyunsaturated fat. Monounsaturated fat increase HDL (high-density lipoprotein), the “good cholesterol” which helps to reduce atherosclerosis and cardiovascular disease. Common sources include olive, canola, and peanut oils. Essential fatty acids are a type of polyunsaturated fat that must be obtained from the diet. Unlike other fats, the body cannot produce omega-3 (linolenic acid) (“good fat”) or omega-6 (linoleic acid) fatty acids (see “bad fats”). Omega-3 is an essential fatty acid found in egg yolk and cold- water fish like tuna, salmon, mackerel, cod, crab, shrimp, and oyster. Omega-3 fatty acids promote a healthy immune system and help protect against heart disease and many other diseases. They also contribute to reduced blood clotting, dilation of blood vessels, and reduced inflammation. Americans tend not to get enough of omega-3 fatty acids. A Mediterranean Diet includes at least two servings of omega-3-rich cold-water fish per week.
Saturated fats are “bad fats” because they increase levels of LDL (low-density lipoprotein), the “bad” cholesterol which leads to atherosclerosis and cardiovascular disease. These fats contain no double bonds between carbon atoms making them typically (but not always) solid at room temperature and very stable. Think of a stick of butter as an example. Foods high in saturated fat include red meat, full-fat dairy products, and tropical oils like coconut and palm. Saturated fat should be avoided with no more than about 10% of total daily calories from saturated fat.
Trans fat, listed as “partially-hydrogenated” oil on a food ingredient list, result from a man-made effort to make unsaturated fat solid at room temperature in an effort to prolong its shelf life. The process involves breaking the double bond of the unsaturated fat. The product is a heart-damaging fat that increases LDL cholesterol even more than saturated fat. Due to legislation requiring food manufacturers to include the amount of trans fat on the nutrition label if it is more than 0.5g per serving, many processed foods that used to be high in trans fat such as chips, crackers, cakes, peanut butter, and margarine are now “trans-fat free.” Check the label and look on the ingredients list for “partially hydrogenated” oil to determine if a food still contains trans fat. If so, avoid that food.
One of the essential fatty acids, the polyunsatured fat omega-6 is found in flax seed, canola, and soybean oils and green leaves. Both the heart-healthy omega-3 and less heart-healthy omega 6 polyunsaturated fats decrease total cholesterol, LDL cholesterol, and HDL cholesterol. Both also are used to make eicosanoids. Eicosanoids are oxygenated fatty acids that the body uses to signal cellular responses. Those eicosanoids made from omega-6 tend to cause inflammation and increase blood pressure and blood clotting. Eicosanoids made from omega-3 have the opposite effect as they reduce blood clotting, dilate blood vessels, and reduce inflammation. This balancing act between omega-6 and omega-3 is essential for maintaining normal circulation and other essential processes. The problem is that most Americans consume an abundance of omega-6 fatty acids and not enough omega-3 fatty acids. Reducing consumption of omega-6 fatty acids and increasing consumption of omega-3 fatty acids may lower chronic disease risk.
In sum, what kinds and how much fat to eat is not as simple as we once thought. The old rule of the thumb that “all fat is bad” has proven incorrect. For weight management it still comes down to calories, regardless if they come from fat, protein, or carbohydrate, you must consume fewer calories than you expend to lose weight. But for optimal health, it turns out that the equation is a little bit more complicated.
Natalie Digate MuthContributor
Natalie Digate Muth, MD, MPH, RD, FAAP is the Senior Advisor for Healthcare Solutions for the American Council on Exercise, a board-certified pediatrician and Fellow of the American Academy of Pediatrics, a Diplomat of the American Board of Obesity Medicine, registered dietitian and board-certified specialist in sports dietetics, and ACE Certified Health Coach. She is the author of "Eat Your Vegetables and Other Mistakes Parents Make: Redefining How to Raise Healthy Eaters" and the textbook "Sports Nutrition for Health Professionals." She has been ACE certified since 1998.