Seed oils like sunflower, linseed, grapeseed, and canola are vegetable oils extracted from plant seeds. They’re widely used for cooking and various other purposes. However, some argue that seed oils may not be beneficial, comparing their production process to that of motor oil.
Dr. Layne Norton, a PhD in Nutritional Sciences, delved into the research-backed health benefits of seed oils in late December 2024.
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Study Dissection
A recent study published in the British Journal of Nutrition examined individuals with non-alcoholic fatty liver disease and compared the effectiveness of three treatment approaches: (1)
- The Standard of Care: Government dietary guidelines on limiting sugar-rich foods, increasing polyunsaturated (PUFAs) and monounsaturated (MUFAs) fatty acids intake, and reducing saturated fatty acids (SFAs) to promote a healthier diet.
- 5:2 Diet (e.g., intermittent fasting)
- Low-Carb, High-Fat Diet
All the diets aimed to provide approximately 1,900 calories per day for men and 1,600 calories for women. The low-carb, high-fat diet comprised 50% to 80% fat, 10% to 40% protein, and minimal carbohydrates. Following the 5:2 diet, female participants consumed 500 calories; males consumed 600 calories on two designated days each week. On the remaining five days, female participants consumed 2,000 calories, while male participants consumed 2,400 calories.
Researchers collected blood samples and analyzed plasma fatty acid content to track changes in liver fat based on the proportion of saturated (SFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fats in the participants’ diets.
Results
After twelve weeks, researchers analyzed the participants’ liver stiffness and fat content changes. While there were minimal differences between the three groups overall, the study found a link between changes in liver stiffness fat content and specific fatty acid concentrations. Notably, higher dietary intake of saturated fats was associated with smaller reductions in liver fat and stiffness. Despite this, all groups experienced improvements due to weight loss and reductions in body mass index (BMI).
Participants who consumed more saturated fat or had elevated plasma levels of saturated fat showed less improvement than those who consumed more unsaturated fats. This was particularly evident with omega-6 polyunsaturated fatty acids (PUFAs), especially alpha-linolenic acid (ALA), demonstrating the strongest association with reduced liver stiffness and fat content. These beneficial fats are commonly found in seed oils.
Significantly, while the improvements across all groups were primarily attributed to weight loss, researchers adjusted for changes in BMI to ensure the findings were not solely due to weight reduction. Even after accounting for BMI differences, the associations with omega-6 PUFAs and ALA persisted, as did the relationship with saturated fats. This underscores specific fatty acids’ role in improving liver health.
Take Home
Arguing that seed oils are harmful based solely on their production process is ultimately irrelevant. “It doesn’t matter how something’s made; what matters is whether it has positive or negative effects on the thing we are measuring,” Dr. Norton explained.
Omega-6 PUFAs benefit liver fat and stiffness in individuals with non-alcoholic fatty liver disease, especially when compared to the effects of saturated fats.
Concerns About Omega-6
Some argue that omega-6 fatty acids in seed oils can oxidize and become rancid, potentially leading to inflammation and the production of free radicals in the body.
Dr. Norton referenced four studies where participants consumed PUFAs from seed oils, such as alpha-linolenic acid, instead of saturated fats, with results that showed no harmful effects on metabolic health or inflammation. The outcomes were either neutral or beneficial. (2)(3)(4)(5)
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References
- Tillander, V., Holmer, M., Hagström, H., Petersson, S., Brismar, T. B., Stål, P., & Lindqvist, C. (2024). Associations between dietary fatty acid and plasma fatty acid composition in non-alcoholic fatty liver disease: secondary analysis from a randomised trial with a hypoenergetic low-carbohydrate high-fat and intermittent fasting diet. The British journal of nutrition, 132(4), 1–13. Advance online publication. https://doi.org/10.1017/S0007114524001673
- Mozaffarian, D., Micha, R., & Wallace, S. (2010). Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS medicine, 7(3), e1000252. https://doi.org/10.1371/journal.pmed.1000252
- Masson, C. J., & Mensink, R. P. (2011). Exchanging saturated fatty acids for (n-6) polyunsaturated fatty acids in a mixed meal may decrease postprandial lipemia and markers of inflammation and endothelial activity in overweight men. The Journal of nutrition, 141(5), 816–821. https://doi.org/10.3945/jn.110.136432
- Pigsborg, K., Gürdeniz, G., Rangel-Huerta, O. D., Holven, K. B., Dragsted, L. O., & Ulven, S. M. (2022). Effects of changing from a diet with saturated fat to a diet with n-6 polyunsaturated fat on the serum metabolome in relation to cardiovascular disease risk factors. European journal of nutrition, 61(4), 2079–2089. https://doi.org/10.1007/s00394-021-02796-6
- Bjermo, H., Iggman, D., Kullberg, J., Dahlman, I., Johansson, L., Persson, L., Berglund, J., Pulkki, K., Basu, S., Uusitupa, M., Rudling, M., Arner, P., Cederholm, T., Ahlström, H., & Risérus, U. (2012). Effects of n-6 PUFAs compared with SFAs on liver fat, lipoproteins, and inflammation in abdominal obesity: a randomized controlled trial. The American journal of clinical nutrition, 95(5), 1003–1012. https://doi.org/10.3945/ajcn.111.030114
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