Once upon a time, I had used to take refined vegetable oils for cooking as heart-healthy. But when I did more research on fats and oils, it hard hit on my belief. I have a mindset of accepting facts even it goes against my belief. From then I thought to write an article on this. And after many years I am going to write about this with this article Cooking oil with polyunsaturated fats, aldehydes & lifestyle diseases. Although polyunsaturated fatty acids (PUFA) are found in different types of cooking oils, these types of fatty acids are predominantly found in most vegetable oils. If you look at the past, you will see vegetable oils are a comparatively newer addition to our diet.
Although we need polyunsaturated fatty acids as essential fats, polyunsaturated fatty acids don’t fit as cooking a medium. Polyunsaturated fatty acids are promoted as heart-healthy, but there is a lesser-known dark side. A big reason is the generation of toxic aldehydes. , we will go through why I am telling this.
Cooking oil with polyunsaturated fats, aldehydes & lifestyle diseases
Before moving further let’s have a glimpse of types of fats
- Saturated fats(SFA): no double bonds in the carbon chain (common source: dairy fats, animal fats, coconut oil)
- Monounsaturated fats(MUFA): one double bond in the carbon chain (example: Oleic acid, olive oil)
- Polyunsaturated fats(PUFA): two or more double bonds in the carbon chain (Example: Linoleic acid or omega-6, omega-3 groups (Alpha-Linolenic acid, Eicosapentaenoic acid or EPA, Docosapentaenoic acid or DHA)-mostly vegetable oils
While choosing a cooking oil, I am more concerned about safety matters than healthy. Here I am not talking about the crucial omega 3 to omega 6 ratio, that I had written earlier. The following points I found as crucial while choosing oils for cooking.
Polyunsaturated fatty acids are less stable and easily oxidized
Due to two or more double bonds in the carbon chain, polyunsaturated fatty acids are less stable and more reactive to oxygen and heat. As oxidation mostly occurs in double bonds, polyunsaturated fatty acids have the least resistance to oxidation. Consequently, the risk of oxidation increases with the number of double bonds present in the fatty acid. (1) Oxidation of fatty acid means the production of the harmful components. Oil with a higher amount of omega 6 polyunsaturated fatty acids like Linoleic acid (LA), Alpha Linoleic acid are less stable and more easily damaged by heat and oxidation.
Cooking oil with polyunsaturated fats, aldehydes & lifestyle diseases: Polyunsaturated fatty acids release a high amount of aldehydes when heated
During heat-generating cooking practices, toxic aldehydes are generated as a result of oxidation of fats or oil. Oral intake of such highly toxic reactive aldehydes enters into blood circulation after absorption in the intestine. Regular ingestion of such toxic compounds increases oxidation and so the oxidative stress inside the body. (2) And increased oxidation or oxidative stress is known to promote cellular damage by inducing DNA damage, protein alteration, and fatty acid oxidation. Similarly, increased oxidation with an increased entry of such toxic compounds like aldehydes further causes damage to tissues, organs, and early aging. Indeed, their toxic pro-inflammatory results promote adverse health effects in a broad spectrum, including impairment of metabolic health, promote cancer, cardiovascular disease, the induction of gastropathic properties such as peptic ulcers and more.
Many studies provide a high level of evidence for the adverse health risks presented by these food toxins. Many scientists, health experts had warned about the toxic effects. Since less stable polyunsaturated fatty acids are much more susceptible to heat degradation than other types of fatty acids, cooking with oil with a higher amount of polyunsaturated fatty acids, produce the highest levels of hazardous toxic compounds. And more high heat or deep-fried involves more toxic compound forms. (3, 4, 5, 6, 7)
Read more about other foods that cause inflammation and lead to cell damage.
Vegetable oils, Polyunsaturated fatty acids, and toxic hydroxynonenal
With recent developments, high heating cooking of oils with omega-6 polyunsaturated fatty acids generates a toxic compound called hydroxynonenal, an aldehyde as a result of oxidation of fatty acids. Hydroxynonenal is considered an important marker of oxidative stress, an inflammatory stimulant, a contributory agent to several diseases, including Alzheimer’s. (8, 9)
Hydroxynonenal inhibits the cell’s ability to recycle damaged proteins and stabilize cell components like the lysosomal membrane. And recycle, or autophagy failure due to daily consumption of omega-6 rich vegetable oils in the progression of cell death has been reported. Neuronal death to Alzheimer’s disease has been suggested with particular attention to hydroxynonenal. Excessive consumption of deep-fried foods that release such toxic compounds is regarded as the top contributing factor in the development of lifestyle diseases like Alzheimer’s disease, type 2 diabetes, obesity, and other metabolic diseases. (10,11,12) Those diseases are commonly linked with toxins, inflammations, cell damage, enlarged fat cells, and more.
Moreover, a 2020 paper published in the journal of Foods demonstrated oxidized oils high with polyunsaturated fatty acid induce neuronal cell death and apoptosis, a form of programmed cell death. (13)
Comparison of aldehyde generation among polyunsaturated, monounsaturated and saturated fats
Almost all oils generate aldehydes when heated. However, due to no or lesser number of the double bond, saturated and monounsaturated fatty acids naturally offer better resistance to heat and oxidation. In a study, researchers compared mono-unsaturated fatty acids-rich culinary algae oil with some other oils such as sunflower, corn with a higher percentage of polyunsaturated fatty acids. They found cooking oil with a higher percentage of PUFA produced a much broader pattern of toxic aldehydes. For example, they found PUFA-rich sunflower oil heated for a period of 90 min produced reactive aldehydes to a much higher level than monounsaturated fatty acid-rich algae oil. (14)
In another study researchers at De Montfort University found PUFA dominated oils had produced much higher aldehydes in comparison to oils that had saturated fatty acids as major when heated for periods of 0–90 min at 180 °C. (15)
Smoke Point of cooking oil
The smoke point is the temperature at which oil starts to produce smoke. When cooking oil reaches the smoke point, it’s biochemical structure changes dramatically and releases toxic compounds. I prefer cooking oil that has a naturally higher smoke point.
However, the smoke point of oils can be a little tricky. The smoke point of cooking oils is also raised during the industrialization process by adding hydrogen atoms in the reactor. (16) In the refining process, oils are also heated to remove the volatile compounds for longer self-life and higher smoke points. But, oil can go to several industrial processes during which delicate fatty acids in oils can be already damaged.
During the industrialization of oil, oil can go through several steps like chemical oil extraction, refining then goes through processes such as bleaching, high temperature deodorizing, and high heat involvement. And oil can go through a temperature range of 240-300°C during the industrialization process. (17)Although many constituents of edible oils interact readily with air or other components to oxidize, antioxidants like vitamin E, Carotenoids in oil resist this process and thus help to preserve the oil quality. (18)However, refined oils are more susceptible to oxidation because refining removes their natural antioxidants. Antioxidants in oils prevent fatty acids from oxidation. (19) Some manufacturer practices adding of antioxidant vitamins in the later stage. But before that oil already can go rancid. In natural form, more stable oil means less oxidation.
When it comes to cooking, I don’t prefer oils with a high amount of polyunsaturated fatty acids as cooking oil. And personally I don’t use those oils. I prefer to take polyunsaturated fatty acids directly from nuts, seeds, fish oil, and algae oil. Saturated fatty acids and monounsaturated fatty acids provide better resistance to heat as well as oxidation. Excessive intake of saturated fats is not preferable. So, we need to balance somewhere in-between. Also, I prefer minimally processed oils like the cold press, wood press, expeller press, etc over chemical extraction and high heat involvement industrial process.
Disclaimer: Information provided here are generalized information for informational and entertainment purpose only, not intended to provide one to one health consultation or replace practice of a qualified practitioner.Different people may have different health condition and may have different reaction to the same food. Hence it has been advised to consult with health care provider before application of any of above information Source and references: 1.A., Malvis & Simon, Peter & Dubaj, Tibor & Sládková, Alexandra & Haz, Ales & Jablonsky, Michal & Sekretár, Stanislav & Schmidt, Stefan & Kreps, Frantisek & Burčová, Zuzana & Hodaifa, Gassan & Surina, Igor. (2019). Determination of the Thermal Oxidation Stability and the Kinetic Parameters of Commercial Extra Virgin Olive Oils from Different Varieties. Journal of Chemistry. 2019. 1-8. 10.1155/2019/4567973 2.Moumtaz S, Percival BC, Parmar D, Grootveld KL, Jansson P, Grootveld M. Toxic aldehyde generation in and food uptake from culinary oils during frying practices: peroxidative resistance of a monounsaturate-rich algae oil. Sci Rep. 2019;9(1):4125. Published 2019 Mar 11. doi:10.1038/s41598-019-39767-1 3.O'Brien PJ, Siraki AG, Shangari N. Aldehyde sources, metabolism, molecular toxicity mechanisms, and possible effects on human health. Crit Rev Toxicol. 2005;35(7):609-662. doi:10.1080/10408440591002183 4.GROOTVELD, M., SILWOOD, C.J., ADDIS, P., CLAXSON, A., SERRA, B.B. and VIANA, M. (2001), HEALTH EFFECTS OF OXIDIZED HEATED OILS1. Foodservice Research International, 13: 41-55. doi:10.1111/j.1745-4506.2001.tb00028.x 5.Grootveld M, Percival BC, Grootveld KL. Chronic non- communicable disease risks presented by lipid oxidation products in fried foods. Hepatobiliary Surg Nutr. 2018;7(4):305-312. doi:10.21037/hbsn.2018.04.01 6.Yamashima T, Boontem P, Shimizu H, Ota T, Kikuchi M, et al. (2020) Vegetable Oil-derived ‘Hydroxynonenal’ Causes Diverse Cell Death Possibly Leading to Alzheimer’s and Related Lifestyle Diseases. J Alzheimers Dis Parkinsonism 10: 483 7.Nowak JZ. Oxidative stress, polyunsaturated fatty acids-derived oxidation products and bisretinoids as potential inducers of CNS diseases: focus on age-related macular degeneration. Pharmacol Rep. 2013;65(2):288-304. doi:10.1016/s1734-1140(13)71005-3 8.Shoeb M, Ansari NH, Srivastava SK, Ramana KV. 4-Hydroxynonenal in the pathogenesis and progression of human diseases. Curr Med Chem. 2014;21(2):230-237. doi:10.2174/09298673113209990181 9.https://en.wikipedia.org/wiki/4-Hydroxynonenal 10.Tetsumori Yamashima, Tsuguhito Ota, Eishiro Mizukoshi, Hiroyuki Nakamura, Yasuhiko Yamamoto, Mitsuru Kikuchi, Tatsuya Yamashita, Shuichi Kaneko, Intake of ω-6 Polyunsaturated Fatty Acid-Rich Vegetable Oils and Risk of Lifestyle Diseases, Advances in Nutrition, , nmaa072, https://doi.org/10.1093/advances/nmaa072 11.Yamashima T (2017) Vegetable Oil: The Real Culprit behind Alzheimer’s Disease. J Alzheimers Dis Parkinsonism 7: 410. DOI: 10.4172/2161-0460.1000410 12.Yamashima T (2020) Possible Prevention of Alzheimer’s Disease by Aldehyde Dehydrogenase: A Perspective Review. J Alzheimers Dis Parkinsonism 10: 489 13.Ueno Y, Kawamoto Y, Nakane Y, et al. Oxidized Perilla and Linseed Oils Induce Neuronal Apoptosis by Caspase-Dependent and - Independent Pathways. Foods. 2020;9(5):538. Published 2020 Apr 26. doi:10.3390/foods9050538 14.Moumtaz S, Percival BC, Parmar D, Grootveld KL, Jansson P, Grootveld M. Toxic aldehyde generation in and food uptake from culinary oils during frying practices: peroxidative resistance of a monounsaturate-rich algae oil. Sci Rep. 2019;9(1):4125. Published 2019 Mar 11. doi:10.1038/s41598-019-39767-1 15.Grootveld M, Percival BC, Grootveld KL. Chronic non- communicable disease risks presented by lipid oxidation products in fried foods. Hepatobiliary Surg Nutr. 2018;7(4):305-312. doi:10.21037/hbsn.2018.04.01 16.https://en.wikipedia.org/wiki/Vegetable_oil 17.© FAO 1994, Processing and refining edible oils,Chapter 5 : Processing and refining edible oils, Report of a joint expert consultation, Organized by the Food and Agriculture Organization of the United Nations and the World Health Organization Rome, 19- 26 October 1993, http://www.fao.org/3/v4700e/v4700e0a.htm 18.Processing Edible Oils, by Russell Schaufler, Penn State Extension, Dec. 12, 2013 https://extension.psu.edu/processing- edible-oils 19.https://www.syft.com/detection-edible-oil-oxidation/