Soybean Oil Diet Raises DNA Damage Markers in Mice Compared with Coconut Oil

A 12-week mouse study has found that a diet rich in polyunsaturated fatty acids from soybean oil produced significantly higher levels of a blood DNA damage marker and greater mitochondrial DNA damage in the liver than a diet based on saturated fat from coconut oil. The work, published in the journal Genes and Environment, was carried out by Masatomi Shimizu, Ayako Daizo, Kenichi Kawada, Masayo Ikeda and Petr Grúz, and adds a cautionary note to the widely promoted practice of replacing saturated fats with seed oils for their cholesterol-lowering effects.

The researchers set out to test a long-standing tension in nutrition science. Polyunsaturated fatty acids, particularly the n-6 variety abundant in soybean oil, are recommended because they lower plasma total and esterified cholesterol, changes widely regarded as protective against cardiovascular disease. Yet the same chemical unsaturation that underlies those metabolic effects makes PUFAs highly vulnerable to lipid peroxidation, a chain reaction that generates reactive aldehydes such as 4-hydroxy-2-nonenal, 4-hydroxy-2-hexenal and malondialdehyde. These molecules can react with DNA to form exocyclic adducts, including 1,N6-etheno-2′-deoxyadenosine, or εdA, which are established markers of genotoxicity and potential initiators of carcinogenesis.

To compare the two dietary patterns directly, the team fed three-week-old male C57BL/6J mice isocaloric high-fat diets in which 30 percent of calories came from fat, either coconut oil or soybean oil, for 12 weeks. Eight mice were assigned to each group, and food intake was monitored every three days throughout the experiment. The animals were housed individually under controlled light, temperature and humidity conditions, and all procedures were approved by the Animal Experimentation Committee of Seitoku University. At the end of the feeding period, blood and liver samples were collected for biochemical analysis, gas chromatography of fatty acids, ELISA-based quantification of εdA adducts, a quantitative PCR assay of mitochondrial DNA integrity, and Western blotting of protein adducts derived from lipid peroxidation products.

The metabolic results largely reproduced classical findings. Mice on the soybean oil diet had significantly lower plasma total cholesterol and cholesterol ester than the coconut oil group, but significantly higher plasma triacylglycerol. They also gained more weight on average, with higher feed efficiency and more retroperitoneal fat, although the difference in body weight gain did not reach statistical significance. Total feed intake was almost identical between the groups at 231.7 grams. In contrast, the coconut oil group showed a significant elevation in plasma total ketone bodies, which the authors attribute to hepatic ketogenesis driven by the medium-chain fatty acids characteristic of coconut oil. Liver weight increased more in the saturated fat group, while hepatic cholesterol and triacylglycerol contents did not differ significantly between the diets.

Gas chromatography confirmed that each diet reshaped membrane fatty acid composition in the expected direction. Mice fed soybean oil showed markedly higher levels of linoleic acid, alpha-linolenic acid and arachidonic acid in the liver, along with significantly higher arachidonic acid in erythrocyte membranes, while monounsaturated fatty acids such as oleic acid declined. The coconut oil diet, which contains essentially no essential fatty acids, induced a biochemical state of essential fatty acid deficiency: mead acid, the hallmark of that deficiency, appeared in both tissues, and the triene-to-tetraene ratio was elevated to 1.34 in liver and 0.80 in erythrocyte membranes, values consistent with overt deficiency. Remarkably, despite this biochemical signature and the massive compensatory synthesis of n-9 fatty acids, the deficient mice showed none of the classic symptoms described in the historical literature, such as polydipsia or skin disorders, over the 12-week period.

The genotoxicity findings were the study’s central result. Blood levels of εdA, a DNA adduct formed by the reaction of lipid peroxidation products with DNA, were significantly higher in the soybean oil group than in the coconut oil group. Liver εdA levels showed a similar trend toward higher values in the polyunsaturated fat group, but this difference was not statistically significant. More strikingly, the quantity of an 8.2-kilobase mitochondrial DNA fragment amplified from liver, which serves as an inverse marker of mitochondrial DNA damage, was significantly lower in the soybean oil group, indicating a greater degree of mitochondrial DNA damage in that group. The authors interpret these patterns as consistent with the membrane enrichment in n-6 PUFAs observed on the soybean oil diet, a composition they suggest plausibly heightens susceptibility to lipid peroxidation.

Western blot analysis of liver proteins added nuance to the picture. Protein-bound 4-hydroxy-2-nonenal, a major reactive aldehyde derived from n-6 PUFAs such as linoleic acid, showed a trend toward higher levels in the soybean oil group, but the difference fell just short of significance at P = 0.054. Protein-bound malondialdehyde trended in the opposite direction, toward lower levels in the soybean oil group, also without statistical significance at P = 0.101. Most unexpectedly, protein-bound 4-hydroxy-2-hexenal, which is primarily derived from n-3 PUFAs, was significantly lower in the soybean oil group even though alpha-linolenic acid was markedly increased in their livers. The authors suggest that n-6 PUFA-driven lipid peroxidation predominated under soybean oil conditions, and they also note that the monoclonal antibodies used for detection may cross-react with other adducts, possibly derived from the abundant mead acid in the coconut oil group, so the 4-hexenal result should be interpreted with caution.

The authors frame their findings as evidence of a trade-off between metabolic benefit and genomic risk. In their discussion, they propose that the elevated ketone body levels seen on the coconut oil diet may be mechanistically linked to the lower genotoxicity markers, citing literature indicating that beta-hydroxybutyrate acts as a signaling molecule with antioxidant effects and can promote the expression of genes involved in resistance to oxidative stress. They also point out that saturated fatty acids are chemically resistant to lipid peroxidation because they lack the reactive carbon-carbon double bonds that make PUFAs vulnerable, and that monounsaturated fatty acids such as the oleic acid synthesized by the deficient mice share this stability. At the same time, they acknowledge that the lower cholesterol levels achieved on the soybean oil diet represent a genuine metabolic change that is conventionally considered favorable.

Several limitations deserve emphasis when weighing these results. The study involved young male mice followed for only 12 weeks, with eight animals per diet group and some analyses based on smaller numbers after outlier removal, so the findings cannot be extrapolated directly to long-term health outcomes in humans. The authors themselves note that future studies are needed to establish whether the observed increases in εdA adducts and mitochondrial DNA damage translate into disease processes such as carcinogenesis or aging. They also raise, but do not resolve, a provocative question about whether the recommended intake of essential PUFAs for homeothermic vertebrates may be overestimated, given that their deficient mice remained apparently healthy while synthesizing compensatory fatty acids. What the study does establish is that, in this experimental setting, the choice between two dietary fats measurably shifted markers of endogenous genotoxic stress in parallel with membrane fatty acid composition, and that the diet conventionally framed as the healthier option carried the higher burden of DNA damage markers in the blood and liver.

Subject of Research: Effects of polyunsaturated versus saturated dietary fat on DNA damage markers in mice

Article Title: A PUFA-rich diet increases endogenous genotoxic stress and mitochondrial DNA damage in mice

Article References: Shimizu, M., Daizo, A., Kawada, K., Ikeda, M., & Grúz, P. (2026). A PUFA-rich diet increases endogenous genotoxic stress and mitochondrial DNA damage in mice. Genes and Environment, 48(1), Article 12. https://doi.org/10.1186/s41021-026-00360-4

Image Credits: AI Generated

DOI: 10.1186/s41021-026-00360-4

Keywords: polyunsaturated fatty acids, soybean oil, coconut oil, lipid peroxidation, DNA damage, mitochondrial DNA, etheno DNA adducts, ketone bodies, essential fatty acid deficiency, mouse study, nutrition, genotoxicity