June 2019 Issue
Ask the Expert: Oxidized Oils and Heart Disease
By Toby Amidor, MS, RD, CDN
Today’s Dietitian
Vol. 21, No. 6, P. 8
Q: Some of my clients are asking about oxidized oils. How do oils get oxidized, and do they impact heart health?
A: In the past decade, there’s been growing concern about the effects of consuming vegetable oils that have undergone oxidation, such as canola and olive oils, on heart health. There are many steps throughout processing, storage, and cooking in which oils can be oxidized. Oil processing, fatty acid composition of the oil, and exposure to air, heat, or light, all increase oxidation.1,2 Because unsaturated oils have shorter chain fatty acids than saturated oils, they oxidize more quickly.3 In terms of CVD risk, evidence of harm is limited and controversial, and research still supports the recommendation to replace saturated and trans fats with unsaturated vegetable fats.
Research
Fred Kummerow, PhD, a German-born American biochemist, theorized that oxidized cholesterol (or oxysterols) contributes to heart disease and claimed that his animal and human research showed that consumption of excess polyunsaturated fatty acids from vegetable oils contributes to oxidized cholesterol. In a 2013 review article, he posited that oxidized lipids double heart disease risk by increasing calcium deposits on the arterial walls (leading to atherosclerosis) and interrupting blood flow (contributing to heart attack and death). Kummerow explained that oxidized cholesterol encourages production of sphingomyelin—a phospholipid found in the cellular membrane of the coronary artery—enhancing the interaction between the membrane and ionic calcium and therefore increasing the risk of calcification in the arteries.4
Kummerow’s theory isn’t without controversy. A 2018 article reviewed results from observational studies and concluded that a high intake of omega-6 polyunsaturated fatty acids, compared with saturated fats or carbohydrates, is associated with a lower risk of cardiovascular events. The authors asserted that intervention studies also suggest that omega-6 fats reduce concentrations of LDL cholesterol in a dose-dependent manner compared with carbohydrates.5
Recommendations for Clients
Although debate continues regarding the risks of consuming unsaturated fat, guidelines still suggest replacing saturated and trans fats with unsaturated fats in the diet. The 2015–2020 Dietary Guidelines for Americans (DGA), the Food and Agriculture Organization of the United Nations and World Health Organization, and the American Heart Association all make this recommendation.6-8 That said, the DGA limits vegetable oil consumption to 27 g per day on a 2,000-kcal diet.6
If clients still are worried about the risks of vegetable oil oxidation, there are several steps RDs can suggest to minimize oxidation. Oils should be stored in a cool, dry place out of sunlight and away from the stove (or other heat source). Olive or vegetable oil can be stored for six to 12 months unopened in the pantry, three to five months in the pantry after opening, or four months in the refrigerator after opening. Canola oil can be stored unopened for one year in the pantry, while nut oils can be stored six to 12 months in the pantry, three to eight months in the pantry after opening, and six to eight months in the refrigerator after opening.9 If clients purchase large containers of oil that go unused for longer, recommend they buy smaller amounts and replenish regularly as needed.
— Toby Amidor, MS, RD, CDN, is the founder of Toby Amidor Nutrition (http://tobyamidornutrition.com) and a Wall Street Journal best-selling author. Her four cookbooks are Smart Meal Prep for Beginners, The Easy 5-Ingredient Healthy Cookbook, The Healthy Meal Prep Cookbook, and The Greek Yogurt Kitchen. She’s a nutrition expert for FoodNetwork.com and a contributor to U.S. News Eat + Run, Muscle&Fitness.com, and MensJournal.com.
References
1. Nawar WW. Chemical changes in lipids produced by thermal processing. J Chem Educ. 1984;61(4):299-302.
2. Choe E, Min DB. Mechanisms and factors for edible oil oxidation. Comp Rev Food Sci Food Safety. 2006;5(4):169-186.
3. Leyton J, Drury PJ, Crawford MA. Differential oxidation of saturated and unsaturated fatty acids in vivo in the rat. Br J Nutr. 1987;57(3):383-393.
4. Kummerow FA. Interaction between sphingomyelin and oxysterols contributes to atherosclerosis and sudden death. Am J Cardiovasc Dis. 2013;3(1):17-26.
5. Maki KC, Eren F, Cassens ME, Dicklin MR, Davidson MH. ω-6 polyunsaturated fatty acids and cardiometabolic health: current evidence, controversies, and research gaps. Adv Nutr. 2018;9(6):688-700.
6. US Department of Health & Human Services. Dietary Guidelines for Americans 2015–2020: Eighth Edition. http://health.gov/dietaryguidelines/2015/guidelines/. Published January 7, 2016.
7. Fats and fatty acids in human nutrition. Proceedings of the Joint FAO/WHO Expert Consultation. November 10-14, 2008. Geneva, Switzerland. Ann Nutr Metab. 2009;55(1-3):5-300.
8. The skinny on fats. American Heart Association website. https://www.heart.org/en/health-topics/cholesterol/prevention-and-treatment-of-high-cholesterol-hyperlipidemia/the-skinny-on-fats?s=q%253Dvegetable%252520oil%2526sort%253Drelevancy. Updated April 30, 2017. Accessed April 18, 2019.
9. FoodKeeper app. Foodsafety.gov website. https://www.foodsafety.gov/keep/foodkeeperapp/index.html