Inflammation is thought to be involved in the etiology of many chronic diseases, including heart disease, diabetes and some cancers. For this reason, the changing scientific consensus that omega-6 polyunsaturated fat (PUFA) does not promote inflammation, as once thought, is an important development. A new paper showing that the omega-6 essential fatty acid linoleic acid intake is associated with a reduced risk of developing diabetes may put to bed any lingering doubts.1 This issue is germane to users of soybean oil and consumers of soyfoods, because the fat in these products is comprised predominantly of omega-6 PUFA.2
As background, for several decades, thinking has been that linoleic acid promotes inflammation by virtue of its in vivo conversion to arachidonic acid, from which are produced eicosanoids and other compounds that promote inflammation. In contrast, the thinking is that omega-3 fat is anti-inflammatory.3 And, that the ratio of omega-6 fat to omega-3 fat is one measure to assess the inflammatory potential of the diet.4 However, in 2017, the American Heart Association5 reported that little direct evidence supports the notion that linoleic acid is pro-inflammatory and a host of other organizations agree that the ratio of omega-6 to omega-3 fat is not a useful indicator.6-11
A meta-analysis published this summer found that linoleic acid intake, and tissue linoleic acid levels, are associated with a decreased risk of developing diabetes. The analysis included 23 articles and 31 prospective studies and involved nearly 300,000 individuals.1 During the median follow-up period which ranged from four to 32 years, 22,639 participants developed type 2 diabetes mellitus. When comparing the highest versus the lowest intake category, linoleic acid was associated with a 6% decreased risk of diabetes. Also, for each one standard deviation increment in linoleic acid concentration in adipose tissue/blood components, risk was reduced by 15%. Both findings were statistically significant. These findings are consistent with observational studies showing that the replacement of saturated fat with polyunsaturated fat is associated with better glycemic control and increased insulin sensitivity.12
This newly published meta-analysis is notable in and of itself, but especially so because a commentary was written in response to this research. The author, Matthias Schulz, from the University of Potsdam in Germany, appropriately emphasized that “conclusions from the meta-analysis regarding a role of higher LA [linoleic intake] in the diet as a measure to prevent diabetes may need to be made cautiously.”13 There is no arguing with this sentiment, especially because observational studies are not designed to establish cause and effect relationships. However, Dr. Schulz went on to comment that “this important meta-analysis clearly shows that harmful effects of increasing dietary LA should not be expected.”
That last comment is particularly significant because there is persuasive evidence that higher linoleic acid intake is associated with a reduced risk of cardiovascular disease.14 Evidence showing linoleic acid does not increase risk, and may in fact decrease risk, of other chronic diseases such as diabetes, may clear the way for consumers hesitant to use soybean oil because of its high omega-6 fat content.
Finally, there is ample reason to conclude omega-6 fat is not pro-inflammatory. For example, the in vivo conversion of linoleic acid to arachidonic acid is negligible. In other words, research results do not support the concept that increasing linoleic acid intake has an effect on increasing tissue levels of arachidonic acid.15 Furthermore, some of the hormones and other compounds produced from arachidonic acid exert anti-inflammatory effects.5 There is even evidence indicating linoleic acid is anti-inflammatory. For example, de Pablo et al.16 found that among participants of the European Prospective Investigation into Cancer and Nutrition (EPIC), erythrocyte levels of linoleic acid were inversely associated with risk of rheumatoid arthritis, an autoimmune and inflammatory disease.
In conclusion, evidence generated over the past decade shows linoleic acid intake is associated with lower risk of chronic disease and is not pro-inflammatory. The predominant fatty acid in soybean oil, and in the fat in soyfoods, is linoleic acid.
- Mousavi SM, Jalilpiran Y, Karimi E, et al. Dietary intake of linoleic acid, its concentrations, and the risk of type 2 diabetes: A systematic review and dose-response meta-analysis of prospective cohort studies. Diabetes Care. 2021.
- Slavin M, Kenworthy W, Yu LL. Antioxidant properties, phytochemical composition, and antiproliferative activity of Maryland-grown soybeans with colored seed coats. J Agric Food Chem. 2009;57:11174-85.
- Simopoulos AP. Omega-3 fatty acids in health and disease. Prog Clin Biol Res. 1990;326:129-56.
- Simopoulos AP. The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases. Exp Biol Med (Maywood). 2008;233:674-88.
- Harris WS, Mozaffarian D, Rimm E, et al. Omega-6 fatty acids and risk for cardiovascular disease: a science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. 2009;119:902-7.
- de Deckere EA, Korver O, Verschuren PM, et al. Health aspects of fish and n-3 polyunsaturated fatty acids from plant and marine origin. Eur J Clin Nutr. 1998;52:749-53.
- Wang C, Chung M, Lichtenstein A, et al. Effects of Omega-3 Fatty Acids on Cardiovascular Disease. Evidence Report/Technology Assessment No. 94 (Prepared by Tufts-New England Medical Center Evidence-based Practice Center, under Contract No. 290-02-0022). AHRQ Publication No. 04-E009-2. Rockville, MD: Agency for Healthcare Research and Quality. March 2004.
- Institute of Medicine 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. https://doi.org/10.17226/10490.
- Stanley JC, Elsom RL, Calder PC, et al. UK Food Standards Agency Workshop Report: the effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health. Br J Nutr. 2007;98:1305-10.
- Kris-Etherton PM, Innis S, Ammerican Dietetic A, et al. Position of the American Dietetic Association and Dietitians of Canada: dietary fatty acids. J Am Diet Assoc. 2007;107:1599-611.
- EAT FOR HEALTH. Australian Dietary Guidelines Providing the scientific evidence for healthier Australian diets. https://www.eatforhealth.gov.au/sites/default/files/content/n55_australian_dietary_guidelines.pdf. 2013.
- Imamura F, Micha R, Wu JH, et al. Effects of saturated fat, polyunsaturated fat, monounsaturated fat, and carbohydrate on glucose-insulin homeostasis: A systematic review and meta-analysis of randomised controlled feeding trials. PLoS Med. 2016;13:e1002087.
- Schulze MB. Dietary linoleic acid: Will modifying dietary fat quality reduce the risk of type 2 diabetes? Diabetes Care. 2021.
- Wang DD, Li Y, Chiuve SE, et al. Association of specific dietary fats with total and cause-specific mortality. JAMA internal medicine. 2016;176:1134-45.
- Rett BS, Whelan J. Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-type diets: a systematic review. Nutr Metab (Lond). 2011;8:36.
- de Pablo P, Romaguera D, Fisk HL, et al. High erythrocyte levels of the n-6 polyunsaturated fatty acid linoleic acid are associated with lower risk of subsequent rheumatoid arthritis in a southern European nested case-control study. Ann Rheum Dis. 2018;77:981-7.
This blog sponsored by the Soy Nutrition Institute and the United Soybean Board.