February 2015 Issue
Heart-Healthy Oils: They're Not All Created Equal
By Judith C. Thalheimer, RD, LDN
Vol. 17 No. 2 P. 24
Here's an update on what's trending on store shelves and the latest science on the healthful fats they contain.
Supermarket shelves are crowded with different kinds of oils, many claiming to be healthful choices. Each type of oil has a different mix of saturated, monounsaturated, and polyunsaturated fatty acids. In addition, there are refined oils and unrefined oils; high-oleic, fortified, and genetically modified oils; salad oils; and frying oils. Since fatty acids in the diet have a significant impact on heart health, choosing the right oil can be a daunting task for many clients and patients.1 Dietitians can help them unravel the mysteries of the oil aisle and make heart-healthy fats a part of a balanced diet.
All plants use triglycerides to store their excess energy. By pressing or crushing the seeds or pulp of plants, these triglycerides can be extracted as oil.2 There are many different kinds of fatty acids, classified by the length of their carbon chains and the number and position of any double bonds, and no oil has just one type of fatty acid. "We categorize fats as monounsaturated, polyunsaturated, or saturated, but the fats we eat are all a mixture of these types of fatty acids," says Sonya Angelone, MS, RDN, CLT, a spokesperson for the Academy of Nutrition and Dietetics (the Academy). That's important to understand, because when it comes to cardiovascular health, the type of fat is more important than the amount of fat.3
Fatty Acids and Heart Health
"We know that replacing saturated fat in the diet with unsaturated fat decreases cardiovascular disease risk," says Jill Weisenberger, MS, RDN, CDE, FAND, author of 21 Things You Need to Know About Diabetes and Your Heart. Eating foods that contain saturated fats raises LDL cholesterol levels in the blood, increasing the risk of heart attack and stroke.4 The 2010 Dietary Guidelines for Americans, the World Health Organization, and the Academy all recommend that saturated fats shouldn't exceed 10% of total calories.1 The latest guidelines from the American Heart Association and American College of Cardiology recommend limiting saturated fat intake even further, to less than 7% for the general population, and 5% to 6% for those with high LDL cholesterol. For a 2,000-kcal diet, that's about 13 g.5 Although a recent systematic review raised questions about the link between saturated fat intake and coronary heart disease, this review is highly controversial.1,6 (See "Saturated Fat — Not So Bad or Just Bad Science?" in the November 2014 issue of Today's Dietitian.)
"The latest guidelines still recommend decreasing saturated fats and replacing those calories with unsaturated fats, because that's what the totality of the evidence is telling us," says Penny Kris-Etherton, PhD, RD, distinguished professor of nutrition at Pennsylvania State University. "We know that saturated fat intake increases LDL cholesterol, and that any increase in LDL increases risk of heart disease."
Saturated fatty acids typically are associated with animal fats such as lard and butter, but they also make up the majority of fatty acids in coconut, palm, and palm kernel oils. These tropical oils have been touted as healthful choices due to their unusually high proportion of medium-chain triglycerides (MCTs).1 Unfortunately, most of the research on MCTs that can be related to heart health was done on saturated fatty acids with eight and 10 carbon chains. Forty-four percent of the MCTs in coconut oil are actually 12 carbons long. In addition, coconut and palm oils contain a high proportion of cholesterol-raising longer-chain saturated fats.1 Less-refined versions of these oils, such as cold-pressed coconut oil and red palm oil, retain a larger portion of health-promoting minor components such as carotenes, but since they have the same fatty acid profile as refined versions, these oils would still be considered a poor choice for heart health.
However, removing saturated fats is only part of the equation. What replaces those fats in the diet equally is important. "So often people trying to eat less fat end up eating more sugar or other simple carbohydrates," Angelone says. "You can't replace saturated fats with carbs and expect a better health outcome, because carbohydrates increase insulin secretion, which signals the liver to manufacture saturated fat."
According to Kris-Etherton, replacing saturated fats with oils rich in any unsaturated fat will have a positive impact on heart health. "I recently collaborated on a multicenter study in which we compared the effect of traditional canola oil with a version high in monounsaturated fats and one fortified with the polyunsaturated long-chain omega-3 fatty acid DHA," Kris-Etherton says. "While there were some differences, all these oils decreased LDL cholesterol and improved the cardiovascular disease risk profile in participants, because they are all low in saturated fat."
"For heart health, you want to replace saturated fats with polyunsaturated fats, especially the long-chain polyunsaturated fats," Angelone says. "These fatty acids have a very positive effect on the cardiovascular system." The two most common polyunsaturated fatty acids in plant oils are the omega-3 fatty acid alpha-linolenic acid (ALA) and the omega-6 fatty acid linoleic acid (LA).1 Both ALA and LA are essential nutrients, meaning the human body can't make them so they must come from food.1 More than 50% of the fatty acids in cottonseed, soybean, corn, sunflower, safflower, walnut, grapeseed, and flaxseed oil are polyunsaturated.
Omega-3 Fatty Acids
Most of the research on omega-3 fatty acids has been done on the longer-chain omega-3s found in fish. Still, the shorter-chain omega-3 ALA in plants also shows heart-healthy traits. An 11-country study in Europe reported less heart disease in countries that typically use oils high in ALA, and diets rich in ALA have been reported to lower lipid levels, reduce vascular inflammation, and reduce blood pressure in people with high cholesterol.1 "ALA is anti-inflammatory and has other heart-healthy properties, like thinning the blood," Angelone says. "Flaxseed and chia seed oils are particularly good sources. Just remember to keep them cold, because they oxidize easily."
Food lipids are very susceptible to oxidation. The oxidative process limits shelf life and leads to the unpleasant taste and smell of rancidity. It also may raise the risk of cardiovascular disease. Oxidized fatty acids have been shown to speed up atherosclerosis development and are linked to several other negative health effects. How much damage oxidized oils can do to our health is still unclear. Oils that are rich in polyunsaturated fatty acids, such as flaxseed, grapeseed, and walnut, are the most susceptible to oxidation, which is triggered by exposure to light, heat, and oxygen.7 Oils should be stored tightly capped in a cool, dark place, and frying oil never should be reused. Oils high in polyunsaturated fats, especially fish, nut, and flaxseed oils, should be kept in the refrigerator.8
Omega-6 Fatty Acids
Omega-6 LA, the other essential fatty acid in plant oils, is the most highly consumed polyunsaturated fat.1 Safflower, grapeseed, sunflower, wheat germ, corn, walnut, and cottonseed oils are among the highest in omega-6 fatty acids.9
In a 2009 advisory, the American Heart Association reported that consuming 5% to 10% of calories from omega-6 polyunsaturated fatty acids is better for heart health than consuming less.1 LA is found in virtually all foods commonly consumed in the Western diet so the typical intake of omega-6 polyunsaturated fatty acids in the United States doesn't seem to be a problem. "The American Heart Association recommends getting 5% to 10% of calories from omega-6 fatty acids," Weisenberger says. "We're right on target with an intake of about 7% of our calories."
LA can be converted in the body to the longer-chain arachidonic acid (ARA), which is a precursor of prostaglandins that promote inflammation, blood clotting, and blood pressure–raising vasoconstriction.1 It would seem reasonable, then, to worry that dietary LA could be bad for cardiovascular health, but that doesn't appear to be the case. A systematic review of randomized controlled trials found no evidence that LA increased inflammatory markers, and a 2011 review reported dietary LA intake wasn't related to tissue levels of ARA.1 "Inflammation isn't necessarily a bad thing. It's crucial for healing," Angelone says. "People think omega-6s are bad and omega-3s are good, but we need both in balance to keep our immune systems running properly. Omega-6 starts the healing process by alerting the immune system to a problem, then omega-3 takes over."
With the move to eliminate trans fats from foods, the amount of polyunsaturated fats in the American diet could possibly change. Trans fatty acids, mostly manmade artifacts of oil hydrogenation, extend the shelf life of processed foods. "There are a lot of new oils coming out on the market that are pumped up in monounsaturated fats at the expense of polyunsaturated fats, because lower-poly oils are more shelf stable," Kris-Etherton says. "We don't want people decreasing intake of polys too much, because polys are good for us."
The Changing Face of the Oil Aisle
Selective breeding or other genetic modification methods can change the fatty acid profile of oils. For example, rapeseed oil naturally is high in erucic acid, a fatty acid that's toxic in high quantities.10 Rapeseed plants have been bred selectively to produce seeds lower in erucic acid and higher in heart-healthy oleic acid. The resulting product is marketed as canola oil.10 Oils bred to be high in heart-healthy oleic acid, such as high-oleic canola, sunflower, and safflower, are growing in popularity in the processed foods industry, because this monounsaturated fat is more shelf stable than the polyunsaturated fats that typically are dominant in oils.11 As trans fats are removed from processed foods, high-oleic oils are taking their place.11 In addition, modern genetic modification processes are being used to include other types of omega-3 fatty acids in oils. In the United States, the FDA has granted generally recognized as safe status to soybeans genetically modified to produce stearidonic acid, another omega-3 fat.1 According to the Monsanto website, this product, designed to help food manufacturers increase the omega-3 content of processed foods, is in the end stages of research and development.12 The health benefits of stearidonic acid are unclear.1 Several companies are working on inserting genes from microalgae into canola plants to create an oil that contains DHA, the same heart-healthy omega-3 fatty acid found in seafood.13,14 While seeds genetically modified to produce DHA aren't ready for the marketplace, canola oil with marine DHA added to it is already on the shelves.15 A recent multicenter trial showed that DHA-enriched high-oleic canola oil improves lipid profiles and lowers predicted cardiovascular risk.16
The third type of fatty acids, monounsaturated, has been linked to reducing LDL cholesterol and triglycerides and raising HDL cholesterol levels. Diets in which these fatty acids represent more than 12% of energy intake are associated with lower fat mass and decreased blood pressure compared with diets containing less than 12%.1 Monounsaturated fatty acids are found in a large variety of foods, including oils from vegetables, nuts, and seeds. Olive, avocado, and canola oils are high in monounsaturated fats, but the highest levels are found in oils that have been modified to increase levels of oleic acid, such as high-oleic safflower and sunflower oils (see graph). Oleic acid, an omega-9 monounsaturated fatty acid, is one of the most abundant fatty acids found in foods, and accounts for 12% of calories in the American diet.1 Research indicates that oleic acid lowers total and LDL cholesterol when it replaces saturated fats in the diet.1 "We need both polyunsaturated and monounsaturated fats in our diets," Kris-Etherton says. "We don't really know at this point what the most beneficial ratio is, but we do know that any unsaturated fats replacing saturated fats will improve cardiovascular health."
Refined vs Unrefined
Most cooking oils contain no additives, preservatives, or special flavorings. For centuries, heating or crushing the oily parts of plants, like the nuts or seeds, extracted oils. In more modern times, the process of extracting vegetable oils has become much more efficient. Manufacturing cooking oil now involves cleaning, grinding, and pressing the seeds, and extracting the oil with a chemical solvent such as hexane. Most oils are then refined, mixed with an alkaline substance, washed, and filtered, and/or distilled. Refining removes trace elements that give oils an undesirable taste, smell, or color. But oils such as olive, avocado, peanut, palm (known as red palm), sunflower, and coconut can be cold-pressed. This method entails minimal processing. The resulting oils contain more plant chemicals such as antioxidants and sterols that contribute to their healthfulness.17 Unrefined oils are more heart-healthy and flavorful, but less stable. They may need to be refrigerated, and many can't be heated. It's important to keep in mind that unrefined oils have the same fatty acid profile and calorie content as refined.17 From a nutritional standpoint, all oils should be used sparingly, and it's recommended that oils high in saturated fats, whether refined or unrefined, should be avoided.
Research on the impact of specific fatty acids on heart health is ongoing. To date, data support replacing saturated fatty acids with omega-3 and omega-6 polyunsaturated fats. The best omega-3 to omega-6 ratio and how much monounsaturated fat to include in the ideal diet haven't been determined yet. While fats are calorie-dense, they help with the absorption of fat-soluble nutrients, are important in cooking, provide an appealing mouth feel, and aid in satiety. Understanding the impact particular fatty acids have on the cardiovascular system, and knowing which oils contain the highest percentage of each, can help make these liquid fats part of a heart-healthy diet. Dietitians are uniquely positioned to translate this emerging and complex research for their clients, making the oil aisle a less daunting place to shop.1
— Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer, a community educator, and the principal of JTRD Nutrition Education Services.
1. Vannice G, Rasmussen H. Position of the Academy of Nutrition and Dietetics: dietary fatty acids for healthy adults. J Acad Nutr Diet. 2014;114(1):136-153.
2. Plant oils and fats. Cyberlipid website. http://www.cyberlipid.org/glycer/glyc0005.htm
3. US Department of Agriculture, US Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed. Washington, DC: US Government Printing Office; 2010.
4. Saturated fats. American Heart Association website. http://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/HealthyEating/Saturated-Fats_UCM_301110_Article.jsp. Updated January 12, 2015.
5. Eckel RH, Jakicic JM, Ard JD, et al. 2013 AHA/ACC guideline on lifestyle management to reduce cardiovascular risk: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 2014;129(25 Suppl 2):S76-S99.
6. Kupferschmidt K. Scientists fix errors in controversial paper about saturated fats. Science. March 24, 2014. http://news.sciencemag.org/health/2014/03/scientists-fix-errors-controversial-paper-about-saturated-fats
7. Wasowicz E, Gramza A, Hes M, et al. Oxidation of lipids in food. Pol J Food Nutr Sci. 2004;13/54(SI 1):87-100.
8. Bishop K. Everything you need to know about storing oils/fats. Preparedness Pro website. http://www.preparednesspro.com/everything-you-need-to-know-about-storing-oilsfats. Updated November 15, 2012. Accessed August 30, 2014.
9. Foods highest in total omega-6 fatty acids. Self.com website. http://nutritiondata.self.com/foods-000141000000000000000-w.html
10. Zeratsky K. Nutrition and healthy eating: I've read that canola oil contains toxins. Is this true? Mayo Clinic website. http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/expert-answers/canola-oil/faq-20058235. Updated March 27, 2013.
11. Winslow A. What exactly is "high-oleic" oil? Eating made easy website. http://eating-made-easy.com/what-exactly-is-high-oleic-oil/. Updated November 18, 2011.
12. Stearidonic acid (SDA) omega-3 soybeans: currently in phase IV of Monsanto's R & D pipeline. Monsanto website. http://www.monsanto.com/products/pages/sda-omega-3-soybeans.aspx
13. Watson E. Dow: DHA from canola oil still 'some years away.' Nutraingredients website. http://www.nutraingredients-usa.com/Suppliers2/Dow-DHA-from-canola-oil-still-some-years-away. Updated May 31, 2011.
14. Sustainable DHA canola closer to reality. Nufarm website. http://www.nufarm.com/assets/26570/1/Omega-3collaborationupdatereleaseJan2014Final.pdf?download. Updated January 30, 2014.
15. Canola oil with omega-3 DHA. Crisco website. http://www.crisco.com/products/canola-oil-with-omega-3-dha-15-801
16. Jones PJ, Senanayake VK, Pu S, et al. DHA-enriched high-oleic acid canola oil improves lipid profile and lowers predicted cardiovascular disease risk in the canola oil multicenter randomized controlled trial. Am J Clin Nutr. 2014;100(1):88-97.
17. Secrest R. Cooking oil. MadeHow website. http://www.madehow.com/Volume-1/Cooking-Oil.html