October 2018 Issue
Healthful Oils: The Canola Controversy
By Carrie Dennett, MPH, RDN, CD
Today's Dietitian
Vol. 20, No. 10, P. 12
What, if anything, is behind the frightening headlines about this mild-mannered oil?
There's a great deal of negative information in the media and on the internet about canola oil, most of it based on misinterpretation of scientific research—or on no research at all. An article headlined "Stop Using Canola Oil Immediately! Canola Oil Dangers"1 includes assertions about the allegedly deleterious effects of genetically modified (GM) plants, while "Canola Oil Proven to Destroy Your Body and Mind"2 extrapolates heavily from a single mouse study.3 For decades, canola has been criticized via viral e-mails and blog posts because the oil of its parent plant—rapeseed—was used as a motor lubricant in the mid-1900s, even though canola and rapeseed bear little resemblance. What does the science say about canola oil, and how can dietitians best advise patients who wonder what oil to use in their home kitchens?
History
Much of the misinformation about canola stems from the fact that the canola plant is a cultivar of the rapeseed plant, and rapeseed oil contains very high levels of erucic acid, which in large amounts can be toxic to humans. Erucic acid was linked to myocardial lipidosis—an accumulation of lipids in heart muscle fibers that progressively deteriorates and weakens the muscle—in animal experiments back in the 1960s.4
However, canola oil is selectively bred to be low in erucic acid. Breeders developed low-erucic acid rapeseed (LEAR) in the 1960s,4 and in the early 1970s, traditional plant breeding techniques further reduced erucic acid levels.4,5 The resulting oil became known as "canola," a contraction of "Canadian" and "ola," which means oil.4 Neither LEAR nor canola oils have caused myocardial lipidosis in pigs or monkeys but did produce it in male albino rats. However, researchers said this type of rat seems to have a peculiar way of metabolizing vegetable oils, making pigs a more accurate model for evaluating the effects of oils in humans.4
Today, oilseed products that don't contain less than 2% erucic acid and less than 30 micromoles of glucosinolates can't use the term "canola."5 Glucosinolates are phytochemicals that cause an unpleasant sulfur odor during processing and in excess amounts have been linked to thyroid disease,4 despite having health benefits otherwise.6 In 2017, the average level of erucic acid in oilseed products was 0.01%.7 Some farmers still grow high-erucic acid rapeseed, but only under contract for specific industrial uses, such as environmentally friendly lubricants.5
From Field to Bottle
Canola is a member of the Brassicaceae family, which also includes broccoli, cabbages, and cauliflower. It's grown primarily in the prairie regions of western Canada, with some acreage planted in Ontario and the Pacific Northwest and small amounts grown in the midwestern and southeastern United States.5 As the yellow-flowering canola plant matures, it forms what look like small pea pods, each containing about 20 tiny round black or brownish-yellow seeds.5
About 80% of the canola grown in Canada is genetically modified to be herbicide resistant. However, only one gene in the plant has been modified, and genes are proteins. Processing removes all proteins from canola oil, so canola oil made from GM seed is considered equivalent to canola oil from non-GM canola plants.8
Once harvested, canola seeds are rolled or flaked to rupture the seed's cells and make the oil easier to extract. Next, the seeds are cooked and mechanically pressed, which squeezes about 80% of the oil out of the seed. This expeller or "first press" oil then may be further refined to be used as a liquid oil, margarine, or shortening.5 "It's important to know that the steps of extracting and refining plant oils are separate processes," says Shaunda Durance-Tod, MSc, RD, CanolaInfo program manager. "Most expeller-pressed canola oil is also refined, but it's due to the market demand rather than [out of] necessity."
Solvents often are used to remove as much of the remaining oil as possible after mechanical pressing. Food-grade hexane is commonly used because it enables 99% of the oil to be released, although this is controversial because hexane is an airborne pollutant that can harm the ozone layer and has neurotoxic effects if inhaled.9-12 "One thing that people don't realize is that the solvent extraction is done within a closed system and that the hexane is then recovered in a process called desolventization so that it can be reused," Durance-Tod says. Desolventization typically uses steam distillation.13,14 "The hexane is contained within the system, and there isn't any residual hexane in the oil."
Deodorizing with steam is another part of the refining process.14 "Depending on the end use, it's often desirable to consumers or food manufacturers to have a neutral-flavored oil so that the other ingredients stand out and aren't overpowered by the taste of the oil," Durance-Tod says. A very small amount of trans fatty acids are produced during the deodorization process, although the amount isn't considered to be significant.15
For cold-pressed canola oil, the seeds aren't heated before, during, or after the pressing process. Instead, they're cleaned and crushed then pressed slowly to limit friction and avoid raising the temperatures above 140° F (60° C). They don't undergo further refinement and may have a more healthful fatty acid and antioxidant profile. "Canola oil produced in this way has a deep yellow color with a much more distinctive flavor that varies depending on where it was grown," Durance-Tod says. "These oils are suitable when you do want to have the flavor, such as a dip for bread, salads, or even roasting vegetables."
The Science on Health
Canola oil is 62% oleic acid, an omega-9 monounsaturated fatty acid (MUFA); 19% linoleic acid, an essential omega-6 polyunsaturated fatty acid (PUFA); 9% alpha-linolenic acid (ALA), a plant-based omega-3 PUFA; and about 7% saturated fatty acid (SFA).16 Canola oil has the lowest SFA content of any common cooking oil—less than one-half the amount of olive or soybean oil—and the most ALA at 1.3 g per tablespoon. Due to its unsaturated fat content, in 2006 the FDA authorized a qualified health claim for canola oil's ability to reduce the risk of heart disease when used in place of saturated fat.17
A 2014 study published in the British Journal of Nutrition examined whether canola oil could be a reasonable substitute for olive oil as part of a Mediterranean-style diet. Both canola oil and olive oil have similar levels of MUFAs, primarily from oleic acid. Canola oil has the advantage of containing ALA, which evidence increasingly links to cardiovascular health.15,16,18 On the other hand, extra virgin olive oil (EVOO) has the benefit of being produced using pressing at low temperatures, allowing it to retain the phenolic compounds and other components that may reduce inflammation and oxidative stress. Antioxidants in both canola oil and EVOO protect PUFAs from damage when exposed to heat, but EVOO has a more favorable antioxidant-to-PUFA ratio than canola oil, so it retains more antioxidants after cooking.15
Although canola oil has a high smoke point of 468° F, one concern is that its high content of fragile ALA means that it produces two to five times more potentially toxic compounds such as acetaldehyde and acrolein when heated past 350° F, compared with olive oil or EVOO. However, there's no evidence that using fresh canola oil for shallow frying under normal home kitchen conditions poses a health risk.15
Unlike olive oil, studies on canola oil and health generally use biomarkers, not disease incidence or mortality, as outcomes.15 A 2013 review in Nutrition Reviews found that replacing saturated fats with canola oil appears beneficial for decreasing total cholesterol and LDL cholesterol, improving glucose tolerance and insulin sensitivity, and maintaining normal triglyceride levels. However, the results of studies comparing canola oil with other vegetable oils rich in PUFAs or MUFAs are less consistent.19
More recently, data from the Canola Oil Multicenter Intervention Trial found that in subjects at risk of metabolic syndrome, diets high in MUFAs from canola oil or high-oleic canola oil reduced central adiposity and blood pressure more than diets high in PUFAs from flax-safflower oil or corn-safflower oil blends, or from a high-oleic canola oil enriched with the omega-3 DHA.20 However, the trial didn't include olive oil in the comparison.
There are currently no intervention or observational studies to show that canola oil has the same cardiovascular health benefits as EVOO. Canola oil's observed benefits on CVD biomarkers likely are due to its ALA content.15 While the research is clear that substituting PUFAs for saturated fats reduces CVD risk, the evidence for MUFAs, while promising, would benefit from more clinical trials.18
Bottom Line
While canola oil doesn't have equivalent health benefits as EVOO, the bad press is overblown.21 Canola oil is a neutral-flavored oil that's rich in heart-healthy fats, and its versatility makes it equally appropriate for salad dressings, marinades, and cooking at all heats.
— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times, owner of Nutrition By Carrie, and author of Healthy for Your Life: A Holistic Approach to Optimal Wellness.
References
1. Stop using canola oil immediately! 6 canola oil dangers. Dr. Axe website. https://draxe.com/canola-oil-gm/
2. Mercola J. Canola oil proven to destroy your body and mind. Mercola website. https://articles.mercola.com/sites/articles/archive/2017/12/27/canola-oil-health-effects.aspx. Published December 27, 2017.
3. Lauretti E, Praticò D. Effect of canola oil consumption on memory, synapse and neuropathology in the triple transgenic mouse model of Alzheimer's disease. Sci Rep. 2017;7:17134.
4. Dupont J, White PJ, Johnston KM, et al. Food safety and health effects of canola oil. J Am Coll Nutr. 1989;8(5):360-375.
5. Where does canola oil come from? Canolainfo.org website. https://www.canolainfo.org/canola/where-does-canola-oil-come-from.php
6. Dinkova-Kostova AT, Kostov RV. Glucosinolates and isothiocyanates in health and disease. Trends Mol Med. 2012;18(6):337-347.
7. Quality of western Canadian canola 2017 — fatty acid composition. Canadian Grain Commission website. https://www.grainscanada.gc.ca/canola/harvest-recolte/2017/quality-report/hqc17-qrc17-9-en.html. Updated February 26, 2018.
8. Canola: the myths debunked. Canola Council of Canada website. https://www.canolacouncil.org/oil-and-meal/canola-oil/canola-the-myths-debunked/
9. Environmental Protection Agency. Hexane. https://www.epa.gov/sites/production/files/2016-09/documents/hexane.pdf
10. Anderson GE. Solvent extraction. American Oil Chemists' Society Lipid Library website. http://lipidlibrary.aocs.org/OilsFats/content.cfm?ItemNumber=40337. Accessed August 21, 2018.
11. California Environmental Protection Agency, Office of Environmental Health Hazard Assessment, Reproductive and Cancer Hazard Assessment Branch. Consideration of n-Hexane for listing under Proposition 65 as known to cause reproductive toxicity. https://oehha.ca.gov/media/downloads/proposition-65/chemicals/n-hexanehid090117.pdf. Published September 2017.
12. Wakelyn PJ, Wan PJ. Edible oil extraction solvents: FDA regulatory considerations. Inform. 2004;15(1):22-23.
13. Unger EH. Processing. In: Daun JK, Eskin NAM, Hickling D, eds. Canola: Chemistry, Production, Processing, and Utilization. Urbana, IL: AOCS Press; 2011:163-188.
14. De Greyt W. Deodorization. American Oil Chemists' Society Lipid Library website. http://lipidlibrary.aocs.org/OilsFats/content.cfm?ItemNumber=40326. Accessed August 21, 2018.
15. Hoffman R, Gerber M. Can rapeseed oil replace olive oil as part of a Mediterranean-style diet? Br J Nutr. 2014;112(11):1882-1895.
16. Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association. Circulation. 2017;136(3):e1-e23.
17. Summary of qualified health claims subject to enforcement discretion. US Food and Drug Administration website. https://www.fda.gov/food/labelingnutrition/ucm073992.htm. Updated February 15, 2018.
18. Kris-Etherton PM, Fleming JA. Emerging nutrition science on fatty acids and cardiovascular disease: nutritionists' perspectives. Adv Nutr. 2015;6(3):326S-337S.
19. Lin L, Allemekinders H, Dansby A, et al. Evidence of health benefits of canola oil. Nutr Rev. 2013;71(6):370-385.
20. Liu X, Kris-Etherton PM, West SG, et al. Effects of canola and high-oleic acid canola oils on abdominal fat mass in individuals with central obesity. Obesity (Silver Spring). 2016;24(11):2261-2268.
21. Liu AG, Ford NA, Hu FB, Zelman KM, Mozaffarian D, Kris-Etherton PM. A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion. Nutr J. 2017;16:53.