Canola Oil: Pros and Cons
By David Ruth
Recently I was telling some friends about my current interest in research related to the effects of dietary proteins, carbohydrates and various kinds of fats on human health. They asked me if I had looked into the possible adverse effects of canola oil. The son of one of my friends told him recently that he thought it very unhealthy to ingest canola oil, and that it was a mistake to think of canola oil as a health food. I said that I remembered hearing something about that controversy, but I had not yet looked into it.
So I began checking various sources for information about the controversy. I started with one of the websites that in the past has most impressed me concerning other issues, “Authority Nutrition” by Kris Gunnars from Iceland. Kris claims to be an “Evidence Based” source of information about nutrition information. She buttresses her claim by referencing peer-reviewed publications for most of the points she makes and by providing direct links to the referenced articles. Kris’s article about Canola (http://authoritynutrition.com/canola-oil-good-or-bad/ ) seemed a balance of good and bad news about the health benefits of canola oil, but it became obvious that Kris had concluded that the healthier alternative was to eliminate canola oil from our diets. After my first reading, she had me fairly convinced that I should avoid using all of the canola oil I had already purchased. Subsequently, however, I re-read her arguments more carefully and looked at the evidence she provided for her conclusion. Here is what Kris had to say [with my comments in bracketed italics]:
- “Most canola oil (about 90%) is produced from genetically engineered rapeseeds.” [This may or may not be a sufficient reason for some to avoid canola oil – though oil that is correctly labeled “Organic” would not, as Kris pointed out in an aside, be genetically engineered.]
- “Most canola oil is made using an industrial process that involves high heat, deodorization and the use of the toxic solvent hexane. In addition, significant amounts of trans fats (up to 4.2% of total fats) are formed during this process.” [The study Kris cites can be found at (http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4522.1994.tb00244.x/abstract ). That study found that the high heat used in processing most canola oils can result both in the production of trans fats and in rancidity (oxidization) that is masked by the deodorization process. Again, however, cold pressed and organic canola oil would not contain such oxidized or trans fats.]
- “Canola oil is low in saturated fats (7%), high in unsaturated fats (63%) and relatively high in polyunsaturated fats (28%) with Omega-6 and Omega-3 fats in a 2:1 ratio.” [These are the numbers that manufacturers tout (with FDA approval) as the main reason why canola oil is a healthy alternative. Kris, however, tries to undermine this claim with the following list of pros and cons:]
- “Although saturated fat has been considered harmful in the past, several recent studies have shown that it really has nothing to do with heart disease. Therefore, the low saturated fat content of canola oil is completely irrelevant, although it does allow for some excellent marketing slogans.” [Kris makes an good point here. The recent studies she cites(http://ajcn.nutrition.org/content/early/2010/01/13/ajcn.2009.27725.abstract ) and (http://archinte.jamanetwork.com/article.aspx?articleid=1108492 ) support her conclusion –but they are obviously not evidence that canola oil is bad for our health.]
- “Unsaturated fats are the healthful kinds of fats found in olive oil.” [The abundance of Monounsaturated Fatty Acids (MUFAs, as they are also called) is the most persuasive evidence that canola oil, at least in its cold pressed form, is good for us. Kris does not argue against this evidence.]
- “The Omega-6/Omega-3 ratio is good, but the type of Omega-3, alpha-linolenic acid (ALA), must be converted to DHA and EPA in order to be useful in humans and we are not able to do this conversion efficiently.” [Kris’s argument is that fatty fish may be better for us than canola oil – but this is not to say that canola oil is not good for us. Although Kris does not document the efficiency argument, a 2006 study in the Proceedings of the Nutritional Society finds that the highest conversion rate was 9% (http://www.ncbi.nlm.nih.gov/pubmed/16441943) ]
- “Keep in mind that although we need some amount of polyunsaturated fats, we absolutely do not need a lot. Eating a lot of canola oil would raise your intake of polyunsaturated fats to unnatural levels, much higher than we were exposed to throughout evolution.” [The source Kris cites for her suggestion that the amount of polyunsaturated fats in canola oil may be too high is not peer reviewed research, but rather the opinion of Stephen Guyenet at (http://wholehealthsource.blogspot.com/2008/09/pracical-approach-to-omega-fats.html ) Stephen does not provide research evidence for his opinion, but rather bases it on what he calls “evolutionary diets”. I think of such diets as good sources of hypotheses to be tested by conducting scientific research, just as I see folk remedies as hypotheses for medical research.]
- Kris cites seven controlled studies show that canola oil lowers LDL cholesterol and triglyceride levels by up to 25%, and that is has no effect on HDL levels [HDL=good, LDL=bad]. She says that these are short-term studies, however, concerning risk factors, not heart disease itself. She sites two longer term studies that she says show such oils can actually increase heart disease in the long term. [One of the two studies cited (http://www.bmj.com/content/346/bmj.e8707 )does show that replacing dietary saturated fat with omega-6 linoleic acid, in the absence of omega-3 fatty acids increases heart disease. The other study (http://www.ncbi.nlm.nih.gov/pubmed/16387724 ) shows that eating more omega-3 fatty acids and less omega-6 lessens the risk of cardiovascular disease. These studies do not provide evidence for Kris’s contention that canola oil can increase heart disease in the long term.]
- Kris concludes: “If you can get your hands on organic, cold-pressed canola oil, then it won’t be as high in oxidized fats and trans fats, so I suppose it is fine to consume. But I definitely wouldn’t make it a large percentage of calories and I would definitely NOT cook with it, as it is still too high in polyunsaturated fats.” And, she continues, “Overall, canola oil is not as bad as other vegetable oils (like soybean oil), but it is still far from being healthy. You would do much better eating olive oil or coconut oil.” [You can see most of Kris’s arguments and evidence at http://authoritynutrition.com/canola-oil-good-or-bad/ Her specific argument about cooking with oils that are high in polyunsaturated fats is that cooking with polyunsaturated fats can result in lipid oxidation and the creation of transfats. This argument is presented at http://authoritynutrition.com/healthy-cooking-oils/ Kris supplies only one reference for her contention that cooking with polyunsaturated fats (PUFA) is not healthful. That reference is to a 2001study published in 2006 in the online Journal of Foodservice. (http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4506.2001.tb00028.x/pdf ) It addresses repeated use of oils by restaurants and therefore may not be relevant in evaluating the healthfulness of cooking at home. Note also that the study was published in an on-line journal that stopped publishing in 2009 and was probably not a peer-reviewed journal.]
Given the very weak evidence that Kris supplied about cooking with PUFAs, I decided to look for more evidence related to the use of canola oil in cooking. At a website called LiveStrong (http://www.livestrong.com/article/184705-canola-oil-health-risks/ ):
- The author cites “a 2014 review article published in Vascular Pharmacology”, saying that it discusses the detrimental effects of heated oils on cardiovascular health, such as vascular inflammation and arteriosclerosis.” [Note that the reference is very vague in that it does not provide enough information to easily find the referenced article, nor does it say that the detrimental effects are anything more than “discussed”. A search of the Journal Vascular Pharmacology for 2014 turned up one article (http://www.sciencedirect.com/science/article/pii/S1537189114000536 ). Like the research cited by Kris, that study dealt with the cardiovascular effects of repeated heating of vegetable oils as happens in fast food facilities. It found that lipid oxidation occurs with repeated heating of such oils.]
So I decided to do my own search for research articles concerning cooking with canola oil. After a fairly exhaustive search I found a study published in the December 2010 issue of Food Chemistry (http://www.sciencedirect.com/science/article/pii/S0308814610006084). The authors studied the formation of trans fatty acids (TFAs) in commercially available canola oil. The results were that negligible amount of TFAs resulted from heating the oil for up to four hours. The results of frying potatoes in the oil were the same. That provided much more authoritative and relevant information about home use of canola oil than both the study cited by Kris and the one referenced by LiveStrong.
Looking at other websites for opinions and information about canola oil:
The section of the Mayo Clinic’s Healthy Lifestyle website on Dietary fats is available at: http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/in-depth/fat/art-20045550
- The Mayo Clinic staff list Saturated Fats and Trans Fats as harmful. They say that Saturated fat raises LDL cholesterol levels (and therefore increase the risk of cardiovascular disease), and that it may also increase the risk of type 2 diabetes. Trans fats, they say, not only raise LDL levels, but such fatty acids reduced HDL levels. [This, of course, is basically in agreement with Kris Gunnar’s analysis, but she counters with the recent studies that show no relationship between saturated fat intake and the diseases themselves.]
- They say that monounsaturated fatty acids (MUFAs) improve blood cholesterol levels, and they may benefit insulin levels and blood sugar control. [Kris agrees that such fatty acids are healthful.]
- They say that polyunsaturated fatty acids (PUFAs) also improve blood cholesterol levels and may also help decrease the risk of type 2 diabetes.
- They mayo staff single out the Omega-3 PUFAs as “especially beneficial to your heart.” They say that the Omega-3 fats found in fish appear to decrease the risk of coronary artery disease and protect against irregular heartbeats. It also helps lower blood pressure levels. [They Mayo staff agree with Kris that plant based Omega-3 fats aren’t converted and used as efficiently as animal based Omega-3 fatty acids.]
- Concerning cooking, the Mayo staff say nothing about the danger of cooking with PUFA. In fact, one of the recommendations is the use canola oil when baking. “Canola oil is also low in saturated fat and has a high proportion of monounsaturated fat, which makes it a healthy and safe choice when it comes to cooking oils.” [Since the Mayo site seems to be regurgitating the official line on saturated fats and makes no reference to recent studies exonerating saturated fats of their role in causing cardiovascular disease, I have to assume that they may not be aware of the conflicting results about cooking with PUFA. So I go to other sites.]
A site called EatingWell has a little article answering the question: How Healthy is Canola Oil Really? (http://www.eatingwell.com/nutrition_health/nutrition_news_information/how_healthy_is_canola_oil_really )
- “The truth is there are no sound scientific studies suggesting a link between canola oil and any disease.”
- “EatingWell often uses canola oil in our recipes because it’s one of the healthiest oil choices. It’s a good source of monounsaturated fats, the kind that, when used to replace saturated fats like butter and cheese, can help reduce “bad” LDL cholesterol levels and lower your risk of heart disease. Canola is the richest cooking-oil source of alpha-linolenic acid, an omega-3 fat that has been linked to heart health.” [No evidence is presented for any of this—so it just seems like it is reproducing the consensus as it has existed until recently.]
One of my favorite sites for medical advice is WebMD. (http://www.webmd.com/food-recipes/canola-oil ) Here is what Stephanie Watson and Kathleen Zelman say about canola oil:
- “Canola oil is one of the best oils for heart health. Made from crushed rapeseeds, it has less saturated fat than any other oil commonly used in the U.S. Check out the numbers: Canola oil has 7% saturated fat, compared to 12% for sunflower oil, 13% for corn oil, and 15% for olive oil. Cutting down on saturated fats helps cut your cholesterol levels. Canola oil is also very high in healthier unsaturated fats.” [Again, this ignores recent evidence about saturated fats.]
- “It’s higher in the omega-3 fatty acid alpha-linolenic acid (ALA) than any other oil except flaxseed oil. ALA is particularly important to have in your diet because your body can’t make it. Studies show that ALA may help protect the heart through its effects on blood pressure, cholesterol, and inflammation.” [No evidence is provided for this conclusion.]
- The FDA allows canola oil makers to label their products with a qualified health claim that there is “limited and not conclusive” scientific evidence that switching out saturated fat for the same amount of canola oil may reduce risk of heart disease. [They go on to say that canola oil is especially good for cooking because of its relatively high smoke point. That smoke point, by the way, is 400 degrees F vs. 380 degrees for olive oil.]
I then looked at a site that had an inflammatory headline about the dangers of canola oil to see if there were any “facts” I hadn’t yet seen. It was at http://www.naturalnews.com/043948_canola_oil_hidden_health_dangers_food_bar.html
Here are the unsubstantiated claims I found:
- Canola depletes vitamin E.
- Canola increases the rigidity of membranes, which can trigger degenerative diseases.
- Because of canola’s high sulfur content, it goes rancid easily, which can exacerbate allergies and compound problems for people with bronchial or asthmatic issues.
- Human studies reveal canola causes an increase in lung cancers.
- Canola can shorten lifespan of animals and lower platelet count.
- Daily canola consumption can raise your triglycerides over 40 percent.
- Canola oil molds quickly and also inhibits enzyme function.
- It opens the door for free radicals, undermining natural antioxidants, and can be linked to increased incidence of many diseases.
- Canola leaves no foul taste when it’s spoiled, so it’s hard to tell if you’re eating rancid erucic acid.
[Since no evidence is presented for these claims, and since other articles on the site claimed such things as: “Tetanus vaccines found spiked with sterilization chemical to carry out race-base genocide against Africans” and “The five biggest lies about Ebola being pushed by government and mass media”, I decided not to follow up on those claims.]
Finally, I decided to look at what Internet Hoax sites have to say about Canola Oil.
A 1999 posting by Dr. Dean Edell (http://www.healthcentral.com/drdean/408/16307.html ) is titled, “Canola Oil: Latest Internet Hoax Victim.” Citing the Internet Hoax Watch Center, Dr. Edell, after listing a number of warnings similar to the above, says, “The bottom line: there’s no scientific evidence that canola oil is unhealthy or bad for us. So hit the delete key if this hoax comes your way.”
At Snopes.com, Barbara Mikkelson says that the internet rumors about the dangers of canola oil are false: “This light, tasteless oil’s popularity is due to the structure of its fats. It is lower in saturated fat (about 6%) than any other oil. Compare this to the high saturated fat content of peanut oil (about 18%) and palm oil (at an incredibly high 79%). It also contains more cholesterol-balancing monounsaturated fat than any oil except olive oil and has the distinction of containing Omega-3 fatty acids, a polyunsaturated fat reputed to not only lower both cholesterol and triglycerides, but also to contribute to brain growth and development. In other words, it’s a healthy oil. One shouldn’t feel afraid to use it because of some Internet scare loosely based on half-truths and outright lies.” The full article, which was updated in August of 2013, is available at: http://www.snopes.com/medical/toxins/canola.asp#swqDIZdOG0mATliu.99
On the website, Urban Legends (http://urbanlegends.about.com/library/blcanola.htm ), Peter Kholer says that behind this internet hoax about canola oil there is a book: Young Again: How to Reverse the Aging Process by John Thomas, first published in 1994 by Plexus Press. Most of the claims circulating on the internet are drawn from the unsubstantiated opinions expressed by Thomas, who proudly proclaims that he is anti-science. Peter systematically refutes the more important claims. [Note, however, that the Hoax articles do not address the issue of extracting the oil using high heat and hexane gas.]
My take-away on all of the above is that unless I someday find any actual evidence about negative effects of cold pressed canola oil, I judge it a quite healthy choice for adding to recipes and for cooking, provided you don’t raise its temperature past its 400 degree F smoke point.
I have, however, become very wary of chemically extracted canola oil and am eliminating it from my diet.