June 2019 Issue
Healthful Fats: The Skinny on Unrefined Plant Oils
By Sharon Palmer, MSFS, RDN
Vol. 21, No. 6, P. 12
It used to be that you had a few choices of cooking oils on supermarket shelves, such as corn oil, soybean oil, and canola oil—all clear, pale, odorless, and tasteless. Then along came the popularity of olive oil, which added a flavorful, unrefined, extra-virgin oil to the options. But today the range of unrefined plant oils has surged dramatically. You can find unrefined, cold-pressed avocado, almond, peanut, grapeseed, hemp, flaxseed, red palm, walnut, and coconut oils in supermarkets—particularly in natural food stores. And you also can find blends of unrefined oils, such as Vega Omega Oil Blend, which is made of unrefined, organic hemp, flaxseed, pumpkin seed, and coconut oils, as well as oils from green tea, black cumin, black raspberry, blueberry, cranberry, and pomegranate. It’s clear that consumers have a wide range of oils to use for cooking, dressing their salads, and topping their pasta. But what are the nutritional implications of these unrefined, cold-pressed oils?
Behind the Labels
Refined oils are those that have been heated and have had chemical solvents applied to extract the oil, producing the best industrial yield from a plant, such as soybeans, sunflower seeds, or corn. However, this process results in the worst-quality oils in terms of health properties, according to Janet Bond Brill, PhD, RDN, FAND, LDN, an expert on heart health and dietary fats and author of Cholesterol Down: 10 Simple Steps to Lower Your Cholesterol in 4 Weeks — Without Prescription Drugs. In contrast, unrefined plant oils are those that are defined as “virgin,” meaning the oil is extracted mechanically without heat or chemical solvents. “Cold” refers to those oils that use no heat during the extraction process. When high temperatures are applied to plants such as olives, there can be a loss of volatile aromas, as well as polyphenols, antioxidants, and vitamins. “Pressed” refers to crushing in a mill in order to obtain the oil.
“Unfortunately, there is no regulation ensuring that unrefined oils are in fact unrefined,” Brill says. The one exception is olive oil. In the European Union (EU), the designations “cold” and “pressed” are regulated for olive oil, Brill explains, but outside of the EU, the regulation for these terms pertaining to olive oil don’t apply, so consumers have no assurance that these statements are true. For assurance, Brill suggests looking for olive oil with the highest polyphenol content (above 500), a free fatty acid level of 0.2% or lower, and peroxides at well below 10 meq/kg. In addition, you can look for certification seals, such as Protected Designation of Origin (or PDO), Protected Geographical Identification (or PGI), Australian Olive Oil Association, the California Olive Oil Council, and Association 3E.
Overall, we know that plant-based oils rich in unsaturated fatty acids, such as sunflower, rapeseed, corn, soybean, and olive, are linked with lower LDL and total cholesterol and triglyceride levels, and higher HDL cholesterol levels, in comparison with less healthful fats such as butter.1 In theory, unrefined plant oils should go beyond mere fatty acid profile benefits, because they contain more of the phytochemical compounds and micronutrients from the original plant. Unfortunately, there isn’t much scientific evidence on the range of unrefined plant oils on shelves today to support this theory, other than for the unrefined plant oil king: extra-virgin olive oil.
The unrefined plant oil with the lion’s share of evidence-based benefits is extra-virgin olive oil. “The scientific data supporting the health benefits of authentic extra-virgin olive oil, plus the existence of regulatory bodies for olive oil, make choosing olive oil as your main fat the best choice—at least until the other oils can compete in terms of data and regulation,” Brill advises. Indeed, hundreds of studies have documented the health benefits of extra-virgin olive oil, a key part of the Mediterranean diet. In 2018, the International Olive Oil Council convened worldwide experts at the Robert Mondavi Institute for Wine and Food Science in California to summarize the data on the human health effects of olive oil consumption. They highlighted the benefits of this oil for CVD, breast cancer, Alzheimer’s disease, and diabetes, in addition to the lifestyle, taste, and cultural benefits related to the Mediterranean diet food traditions.2
Another emerging unrefined oil is from avocado, which has an oil extraction process similar to that of olive oil, explains Brill, who rates this oil as the second best choice after olive oil. Avocado oil extraction involves removing the skin and pit, grinding the flesh to a paste, malaxation (slow churning) for 40 to 60 minutes at 45° to 50° C, and separation using a centrifuge to obtain the oil. This slightly higher temperature doesn’t affect the quality of the oil, Brill says, which has 76% monounsaturates, 12% polyunsaturates, and 12% saturates—very similar to olive oil. The main antioxidant is α-tocopherol, with a minor presence of δ-tocopherol, and components such as chlorophylls and carotenoids.
Other unrefined oils, such as hemp and flaxseed, may have potential benefits related to their plant-based omega-3 fatty acid content. Hemp oil contains 2 g omega-3 fatty acids per tablespoon, and flaxseed oil contains about 7 g per tablespoon. However, these oils often are used as dietary supplements rather than culinary oils.
Not All Unrefined Oils Are Equal
Just because the oil is unrefined, it doesn’t mean the oil has a healthful lipid profile. “My two pet peeves are coconut oil and palm oil,” Brill says. She stresses that the claim that coconut oil is a health food stems from the misconception that coconut oil contains mostly medium-chain triglycerides, so the oil is presumed to have a neutral effect on blood LDL cholesterol levels. In addition, the high amount of lauric acid in coconut oil is presumed to increase HDL cholesterol. “This is simply not the case,” says Brill, who reports that more than 50 years ago the saturated fatty acids lauric acid, myristic acid, and palmitic acid were found to be hypercholesterolemic.3 “Approximately 92% of the fat in coconut oil is saturated, consisting of primarily the big three saturated fatty acids: about 49% lauric acid, 18% myristic, and 9% palmitic.”
Red palm oil may be marketed as another unrefined, healthful oil, but it also has a high percentage of saturated fatty acids—roughly 50% of the total fatty acids are saturated, with a high percentage of palmitic acid (44%).4 “The high percentage of hypercholesterolemic saturated fatty acids in palm oil clearly makes this a poor choice for heart health, regardless of how it’s processed,” Brill says.
What’s the bottom line on these oils? “The claim that the oil is unrefined does not automatically make it a health food. Just because it is from a plant also does not automatically make it a healthful oil,” Brill says.
In the Kitchen
One of the main culinary benefits of unrefined plant oils is the aroma and flavor still present in the oil. So, if you want your stir-fry to taste of peanuts, add unrefined peanut oil. If you want your cookies to taste of walnuts, use unrefined walnut oil. The sky’s the limit for the flavor properties you can gain in numerous dishes, such as salad dressings, marinades, savory recipes, baked goods, stir-fries, side dishes, and pasta dishes.
But how do unrefined plant oils perform in the kitchen? “The more refined the oil, the higher the smoke point,” Brill says. Which means that unrefined oils may lose quality as cooking temperature rises. Indeed, some unrefined oils have quite low smoke points—flaxseed oil is about 225° F. However, many have higher smoke points. For example, the smoke point of olive oil is 410° F, which should cover most cooking done in a home kitchen.
Unrefined plant oils often come with a steep price tag, further highlighting the option of using these oils as a special culinary ingredient rather than as a replacement for all of the fat in a traditional recipe. The high price and sensitivity of many unrefined oils may make them better choices for no-heat culinary uses, such as for salad dressings, finishing pastas, and glazing finished savory dishes. While we’re waiting for the science, recommend extra-virgin olive oil as the No. 1 cooking oil with other heart-healthy options to round out the health and flavor appeal of a plant-based diet.
— Sharon Palmer, MSFS, RDN, is known as the Plant-Powered Dietitian. She recently obtained her MS in Sustainable Food Systems and is the nutrition editor for Today’s Dietitian.
1. Schwingshackl L, Bogensberger B, Benčič A, Knüppel S, Boeing H, Hoffmann G. Effects of oils and solid fats on blood lipids: a systematic review and network meta-analysis. J Lipid Res. 2018;59(9):1771-1782.
2. Visioli F, Franco M, Toledo E, et al. Olive oil and prevention of chronic diseases: summary of an international conference. Nutr Metab Cardiovasc Dis. 2018;28(7):649-656.
3. Mensink RP. Effects of stearic acid on plasma lipid and lipoproteins in humans. Lipids. 2005;40(12):1201-1205.
4. Mancini A, Imperlini E, Nigro E, et al. Biological and nutritional properties of palm oil and palmitic acid: effects on health. Molecules. 2015;20(9):17339-17361.