A Review of Cooking Oil Qualities and Influences on Human Health

Katherine Wohl, RDN, LD, IFNCP

 

The use of various plant-based cooking oils has become a significant component of the modern diet. Oils contribute essential fatty acids (EFAs) and polyphenols that can offer unique health benefits. Each seed, nut, or fruit used as the source for any oil has a variety of qualities that may be influential on cellular physiology, inflammatory pathways, and other areas of human health. Their impact can be either positive or negative on the body based on the different qualities of each, including its composition, processing, refinement, among other factors. Because of their significance in our current diet and their influence on health, it’s important to understand not only what your best choices are, but also why – so you can better navigate the often-confusing public health messaging surrounding them.

 

Why Is This an Important Topic?

 

Over the past 50 years, calories from plant-based oils have risen steeply and even more significantly in more recent years. In fact, it has been the most rapid, sharpest increase in the consumption of any food. (1-4) While the term “vegetable oil” is used as the umbrella term for many of these oils, they are not actually coming from vegetables, but rather seeds, nuts, legumes, and to a lesser extent, fruit. While there are many that fall under this category, some included are corn, soybean, sunflower, safflower, canola, peanut, flaxseed, olive, and coconut oil. Whenever there is a rapid increase in consumption of a particular food, there is evidence to how that food group influences human health – and the impact of oils on the body is no exception.

 

How to Assess Plant-Based Oils

It goes without saying that not all oils are created equal in terms of their quality and potential influence on health. Most of us have been surrounded by messaging suggesting “good” vs “bad” oils in one way or another. Yet, what’s been missing in this conversation is a more thorough assessment of the nutritional and biochemical influences that a particular oil has on the body based on its composition and how it has been processed. To best understand how oils impact on health, its necessary to look more closely at how to assess oils:

  • Omega index (Omega 6: Omega 3 ratio): Seed oils – including safflower, sunflower, corn, cottonseed sesame, peanut, soybean, and canola oil – comprise 90% of oils consumed in North America and are largely made up of omega 6 fatty acids with low levels of omega 3 fatty acids (flaxseed oil being the exception). Elevated ratios are  associated with inflammation and may contribute to physiologic imbalance in the body. (5-6)
  • Influence on eicosanoid production: The fatty acids provided by plant oils lead to the production of eicosanoids – molecules that can be pro-inflammatory or anti-inflammatory in nature. An imbalance in the type of eicosanoids produced, which can happen due to overconsumption of omega 6 fatty acids that produce those that are more inflammatory, may lead to chronic conditions or a compromised immune system. (5)
  • Cell structure, mitochondria, and phospholipid membrane: Mitochondria, small organelles within each cell, are critical to health and when damaged can lead to widespread health implications. A large reason mitochondria become damaged is due to the impact of polyunsaturated fatty acids on the phospholipid bilayer – the membrane that is composed of lipids and surrounds the mitochondria. High intakes of polyunsaturated fatty acids, again linked to the overconsumption of seed oils, creates an unstable membrane that is more susceptible to oxidative stress and influences cellular functioning, driving disease processes. (7-8)
  • Smoke point and polar compounds: Oils are highly sensitive to temperatures which effects where and how they’re used with cooking. The smoke point of an oil refers to the highest temperature an oil can be heated without burning and producing harmful chemicals. Less commonly discussed is polar compounds which should also be used as part of this assessment. When higher levels of polar compounds result from the heating of a particular oil, more free radicals are generated which are harmful to health. It’s important to consider both the smoke point and polar compounds when evaluating cooking with a particular oil. For example, some oils such as canola and grapeseed have very high smoke points and are recommended for high heat cooking; however, the polar compounds generated after heating are very high – making them more damaging than it appears. On the other hand, olive oil, which can be heated to moderate temperatures, generates very low polar compounds and similarly, coconut oil can withstand high heat with low polar compounds created.
  • The impact of food processing: It’s not only the inherent qualities of a particular oil that matter, but what happens to that oil in the way it is processed and refined. Due to the influence of the food industry and the desire for oils without a strong taste that won’t cause separation, most industrial seed oils go through heavy processing where they are refined, bleached, and deodorized (RBD.) This process requires very high levels of heat, often twice the temperature used to create polar compounds, producing excessive amount of lipid peroxidases and forming trans fatty acids, which makes them so damaging. On the other hand, cold-pressed olive oil goes through very little processing and is never refined, bleached, and deodorized – which is why it maintains its flavor and color while also making it a much more favorable choice. (9-10)
  • Polyphenol content: With everything described above, it’s clear certain oils, namely highly processed, omega 6 rich seed oils, can negatively impact the body – drawing on the body’s reserves and requiring more in terms of detoxification. However, the right choice in oils can have a net positive effect on the body because of what they do contain. This is yet another reason that olive oil has rightly been held in high regard – it contains abundant amounts of polyphenols. When vegetables are cooked with olive oil, research has shown a higher level of nutrient bioavailability in the end dish – meaning thar you get more antioxidants than you would if eating the vegetables alone. This speaks to the molecules in plant foods working together synergistically which beneficially impacts our bodies. (11)

The Impact on Human Health

When considering the various qualities of oils described above, it becomes clear why they have such a far-reaching impact on health. While certain oils have the potential to positively influence our physiology, others can help serve to drive inflammation, oxidation, and imbalances that may drive chronic conditions. Perhaps this is most widely discussed in the area of cardiovascular disease risk and the well-known lipid theory that suggests that consuming fats and oils that raise cholesterol levels increase one’s risk for heart disease. More and more research is revisiting this and suggesting a new theory – the oxidized linoleic hypothesis – that heart disease is not simply a matter of cholesterol in the blood, but a function of inflammation, damaged arterial walls, oxidative stress and these together drive heart disease. Further, oxidation starts to become responsible due to the imbalance of linoleic acid in the body. (12-13)

However, oils have a far greater influence on health than heart disease alone. Research has been done in the areas of brain health and bone mineralization and showed negative impacts of higher levels of omega 6 fatty acids. (14-16) Canola oil has been shown to have a negative effect on insulin sensitivity and blood glucose levels. Adult women with type 2 diabetes showed increased inflammation, insulin resistance, and oxidative stress with canola oil compared to olive oil and a separate study which showed that young Australians were 2-3 times more likely to develop metabolic syndrome with regular use of canola or sunflower oil. (17-19) Yet to speak again to the benefits oils can have, olive oil showed favorable outcomes in inflammatory markers and GI symptoms in individuals with IBD. (20) All this to show that there is a very small window of physiologic compatibility with certain oils, and outside of that window, they begin to impact health. (21)

Guidelines for Use of Specific Oils

  • Olive oil, avocado oil, coconut oil and will stand up to modest amounts of heat without the production of free radicals and lipid peroxidases.
  • Flaxseed oil has an excellent omega 6: 3 ratio – because it does not stand up to higher temperatures, it is best use for salad dressing, not cooking.
  • For animal fats, grass fed butter and ghee are very well balanced with a 1:1 omega 6:3 ratio in butter and can be used for higher heat cooking.
  • Remove predominant omega 6 fatty acid sources, including: corn oil, soybean, sunflower, safflower, canola, peanut oil, cottonseed oil, and other vegetable oils.

 

Because oils are so present in our diet, this topic can feel overwhelming if you are just beginning to make changes in your life. The beautiful thing is that once you make the right swaps, it not only becomes a simple part of your lifestyle but also profoundly impacts your health in a positive direction!

The information and resources provided in this article are based on the opinions of the author unless otherwise noted. All information is intended to assist readers to make their own informed  nutrition and health decisions after consulting with their health care provider. All products sold and distributed by Nutritional Medicinals are conventional whole foods and are not intended to diagnose, treat, prevent or cure any disease or condition.

 

References

  1. Modern American Diet Has Gotten Bigger, Heavier on Grains and Fat. 2016. USDA Economic Research Service; Pew Research Center Analysis.
  2. U.S. Trends in Food Availability and a Dietary Assessment of Loss-Adjusted Food Availability, 1970-2014, EIB-166 USDA, Economic Research Service.
  3. Loss-Adjusted Availability of U.S. Calories by Food Group. Updated 2017. USDA, Economic Research Service Loss-Adjusted Food Availability data.
  4. How the American diet has changed since 1970. 2016. USDA Economic Research Service; Pew Research Center analysis.
  5. Gray, B., Steyn, F., Davies, P. et al. Omega-3 fatty acids: a review of the effects on adiponectin and leptin and potential implications for obesity management. Eur J Clin Nutr 67, 1234–1242 (2013).
  6. Tobias Pischon. Circulation. Habitual Dietary Intake of n-3 and n-6 Fatty Acids in Relation to Inflammatory Markers Among US Men and Women, Volume: 108, Issue: 2, Pages: 155-160, DOI: (10.1161/01.CIR.0000079224.46084.C2)
  7. Ting, H., Chen, L., Chen, J. et al. Double bonds of unsaturated fatty acids differentially regulate mitochondrial cardiolipin remodeling. Lipids Health Dis 18, 53 (2019).
  8. Marcus K. Dymond. Mammalian phospholipid homeostasis: evidence that membrane curvature elastic stress drives homeoviscous adaptation in vivo. J. R. Soc. Interface 2016 13 20160228; DOI: 10.1098/rsif.2016.0228. Published 17 August 2016.
  9. Guillaume C., et al. “Evaluation of Chemical and Physical Changes in Different Commercial Oils during Heating”. Acta Scientific Nutritional Health 2.6 (2018): 02-11.
  10. Azizian, H., and Kramer, J. K. G., A Rapid Method for the Quantification of Fatty Acids in Fats and Oil with Emphasis on trans Fatty Acids Using Fourier Transform Near Infrared Spectroscopy (FT-NIR), Lipids, 2005; 40:855-867.
  11. Ramírez-Anaya JDP, Castañeda-Saucedo MC, Olalla-Herrera M, Villalón-Mir M, Serrana HL, Samaniego-Sánchez C. Changes in the Antioxidant Properties of Extra Virgin Olive Oil after Cooking Typical Mediterranean Vegetables. Antioxidants (Basel). 2019;8(8):246. Published 2019 Jul 26. doi:10.3390/antiox8080246
  12. Harris WS and von Schacky C. The Omega-3 Index: A New Risk Factor for Death from CHD? Preventive Medicine 39:212-220
  13. DiNicolantonio JJ, O’Keefe JHOmega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Heart 2018;5:e000898. doi: 10.1136/openhrt-2018-000898
  14. Taha, A.Y. Linoleic acid–good or bad for the brain?. npj Sci Food 4, 1 (2020). https://doi.org/10.1038/s41538-019-0061-9
  15. Varela-López A, Ochoa JJ, Llamas-Elvira JM, López-Frías M, Planells E, Speranza L, Battino M, Quiles JL. Loss of Bone Mineral Density Associated with Age in Male Rats Fed on Sunflower Oil Is Avoided by Virgin Olive Oil Intake or Coenzyme Q Supplementation. Int J Mol Sci. 2017 Jun 29;18(7):1397.
  16. Bullon P, Battino M, Varela-Lopez A, Perez-Lopez P, Granados-Principal S, Ramirez-Tortosa MC, Ochoa JJ, Cordero MD, Gonzalez-Alonso A, Ramirez-Tortosa CL, Rubini C, Zizzi A, Quiles JL. Diets based on virgin olive oil or fish oil but not on sunflower oil prevent age-related alveolar bone resorption by mitochondrial-related mechanisms. PLoS One. 2013 Sep 16;8(9):e74234.
  17. Samarji R, Balbaa M. Anti-diabetic activity of different oils through their effect on arylsulfatases. J Diabetes Metab Disord. 2014;13(1):116. Published 2014 Dec 9.
  18. Atefi M, Pishdad GR, Faghih S. The effects of canola and olive oils on insulin resistance, inflammation and oxidative stress in women with type 2 diabetes: a randomized and controlled trial. J Diabetes Metab Disord. 2018;17(2):85-91.