Seed oils: are they bad for you?

By the Voltra team · Updated 30 September 2026

What the fuss is about

Seed oils are cooking oils such as canola, corn and soybean, which nutrition influencers often criticise [4]. The worries are that they're high in omega-6 fat, which some link to inflammation, and that traces of the chemicals used to extract them may remain after processing [4].

In the US, the dietary guidelines for 2025–2030 say: "When cooking with or adding fats to meals, prioritize oils with essential fatty acids, such as olive oil. Other options can include butter or beef tallow." [5] The same page keeps the limit: "In general, saturated fat consumption should not exceed 10% of total daily calories." [5]

Omega-6 and inflammation

The theory is that the body turns linoleic acid, the main omega-6 in these oils, into arachidonic acid and then into compounds that drive inflammation [6]. The trials that tested it don't show that. A 2012 review of 15 randomised trials in healthy people found no significant changes in a wide range of inflammation markers, including C-reactive protein (CRP) [6]. A 2017 meta-analysis of 30 trials with 1,377 people found no significant effect on CRP or the other markers measured; only in the trials with the biggest increases in linoleic acid might CRP rise [2].

What about the balance of omega-6 to omega-3? A 2010 FAO and WHO expert report found no basis for a specific ratio as long as intakes of both are within its recommended ranges, which for linoleic acid is 2.5% to 9% of daily energy [7]. On 2,000 kcal a day that's about 6 to 20 g of linoleic acid, at 9 kcal per gram of fat (calculated) [7]. The upper figure, 20 g, is the linoleic acid in about 50 g of sunflower oil or 37 g of corn oil (calculated) [8]. For omega-3 from fish, see our omega-3 guide.

Heart disease and cholesterol: what the trials found

WHO funded both Cochrane reviews [9] [10].

The two old trials are the ones critics cite; their data were recovered and re-analysed decades later [11] [12]. In the Sydney trial, which used safflower oil and a safflower-oil margarine, the trans fat in people's diets wasn't recorded [11]. The Minnesota trial ran in six state mental hospitals and a nursing home; replacing saturated fat with corn oil lowered cholesterol but not deaths [12].

On LDL cholesterol the evidence is firmer. WHO rates it as high-certainty evidence that replacing saturated fat with polyunsaturated fat, monounsaturated fat or carbohydrate lowers LDL, and says: "The greatest reduction in LDL cholesterol was observed for polyunsaturated fatty acids, followed by monounsaturated fatty acids and then carbohydrates." [1] A network meta-analysis of 54 trials compared the fats directly: for each 10% of daily energy moved from butter to safflower, sunflower, rapeseed (canola), flaxseed, corn, olive, soybean, palm or coconut oil, or even beef fat, LDL came out 0.23 to 0.42 mmol/L lower, and butter and lard ranked worst; the authors noted the overall low quality of the evidence [13]. Ghee wasn't among the fats tested. For diets built on animal fat, see our carnivore diet guide and keto guide.

Studies that measure linoleic acid in the blood point the same way. Pooling 30 cohort studies with 68,659 people, higher levels were linked with a lower risk of cardiovascular disease, cardiovascular death and ischaemic stroke [14]. That shows a link, not cause and effect, and two of the authors reported research support from Unilever for the work [14].

What WHO and the American Heart Association advise

WHO's 2023 guideline: "WHO recommends that adults and children reduce saturated fatty acid intake to 10% of total energy intake (strong recommendation)." [1] It recommends replacing saturated fat with polyunsaturated fat (a strong recommendation), or with monounsaturated fat from plants or fibre-rich carbohydrate (conditional), and keeping trans fat to 1% of energy (strong) [1]. In the trials behind the polyunsaturated swap, the fat came mainly from plant oils rich in linoleic acid [1]. On 2,000 kcal a day, 10% is about 22 g of saturated fat, the amount in about 36 g of ghee (calculated) [8].

WHO's healthy-diet advice spells out the swap, cutting saturated fat by "replacing butter, lard and ghee with oils rich in polyunsaturated fat, such as soybean, canola (rapeseed), corn, safflower and sunflower oils" [15].

The American Heart Association reached the same view in 2017: trials that replaced saturated fat with polyunsaturated vegetable oil cut cardiovascular disease by about 30%, and it concluded that replacing saturated fat with unsaturated fats, especially polyunsaturated, will lower cardiovascular disease [16]. Its 2021 guidance advises liquid plant oils in place of tropical oils and partially hydrogenated fats [17].

Ghee, olive oil and vegetable oils

USDA FoodData Central [8]. The ghee row is USDA's anhydrous butter oil, which has the full breakdown; USDA's record named clarified butter (ghee), taken from a product label, gives 60 g of saturated fat. Sunflower is USDA's linoleic sunflower oil (under 60% linoleic acid).

USDA FoodData Central [8]: omega-6 is linoleic acid (18:2), omega-3 is alpha-linolenic acid (18:3). USDA's sunflower oils range from 3.6 g of linoleic acid per 100 g (high-oleic) to 65.7 g (high-linoleic).

Ghee and palm oil are about half or more saturated fat. Olive and canola oil are mostly monounsaturated. Corn and soybean oil are mostly polyunsaturated, and this sunflower oil is about 40% polyunsaturated; in all three, 88% to 99% of the polyunsaturated fat is linoleic acid (calculated). Canola and soybean oil also carry some plant omega-3 [8].

The Gulf's own food guides say the same. Kuwait's lists ghee and butter among the saturated fats and says: "Use unsaturated fats and oils while cooking to limit your intake of saturated fats." [18] It also says to cook without added oil where you can, and to use as little as possible [18]. Qatar's advises avoiding saturated and trans fats such as ghee, and says: "Use healthy vegetable oils such as olive, corn and sunflower in moderation." [19] Oman's 2026 guide says: "When cooking or frying, pick vegetable oils which are rich in unsaturated fats, such as canola, sunflower, corn, soy, olive or sesame oil." It also says to limit butter, animal ghee, vegetable ghee and palm and coconut oil [20].

Industrial trans fat comes from partially hydrogenating vegetable oils [1]. WHO has validated the rules Saudi Arabia, Oman and the UAE have put in place to eliminate it from their food supplies [21].

Frying and re-using oil

Saudi Arabia's food and drug authority (SFDA) explains that frying oil changes chemically in storage and when it's exposed to heat and light, forming substances that are harmful to health; the more often oil is used or misused, the more harmful oxidation products form [22]. Oils richer in polyunsaturated fat are more prone to go rancid and form these products, especially when heated [22]. Its advice: fry at 180 °C or less, keep food bits out of the oil, cool it quickly after frying and store it in opaque containers [22]. In 2023 the SFDA also "cautioned against using the oil more than twice" [3].

SFDA [22]. The smoke point drops the more the oil is exposed to air or re-used [22].

Restaurants are checked too: SFDA inspectors test frying oil with a meter, and oil that reads above 24% on its polarity scale is treated as unfit to eat and has to be changed [23].

In Voltra

Cooking fat is easy to leave out when you log a home-cooked dish, and oil and ghee are almost pure fat: USDA gives olive oil 884 kcal and ghee 900 kcal per 100 g [8]. In the Eat tab, search for ghee (سمن), olive oil (زيت زيتون) or sunflower oil and add what you used, or tap Describe and include the oil or ghee in what you type. Voltra sets a daily calorie target for you, and the oil or ghee you log counts toward it.

Frequently asked

Sources

1. World Health Organization (2023). Saturated fatty acid and trans-fatty acid intake for adults and children: WHO guideline. Recommendations and rationale, pp. ix–xii.
2. Su H, Liu R, Chang M, Huang J, Wang X (2017). Dietary linoleic acid intake and blood inflammatory markers: a systematic review and meta-analysis of randomized controlled trials. Food Funct 8(9):3091–3103. Abstract. 30 trials, 1,377 people.
3. Saudi Food and Drug Authority (2023). SFDA offers various recommendations for safe food frying (news, 3 April 2023). Frying advice.
4. Harvard T.H. Chan School of Public Health (2025). Are seed oils healthful or harmful? (news, 27 February 2025). Cited only for what is claimed about seed oils.
5. U.S. Department of Agriculture and U.S. Department of Health and Human Services (2026). Dietary Guidelines for Americans, 2025–2030. Incorporate healthy fats.
6. Johnson GH, Fritsche K (2012). Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials. J Acad Nutr Diet 112(7):1029–41. Abstract. 15 trials in healthy people; funding source not stated in the abstract.
7. FAO and WHO (2010). Fats and fatty acids in human nutrition: report of an expert consultation. FAO Food and Nutrition Paper 91. Summary of conclusions, pp. 16–17.
8. U.S. Department of Agriculture, Agricultural Research Service (2019). FoodData Central, SR Legacy: butter oil, anhydrous (173412), and related oil and fat records. Also 171314 (clarified butter, ghee), 171413 (olive), 171017, 171025 and 172338 (sunflower), 171029 (corn), 172336 (canola), 171411 (soybean) and 171015 (palm).
9. Hooper L, Martin N, Jimoh OF, Kirk C, Foster E, Abdelhamid AS (2020). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev 8:CD011737. Abstract. Funded by WHO.
10. Hooper L, Al-Khudairy L, Abdelhamid AS, et al. (2018). Omega-6 fats for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev 11:CD011094. Abstract. Funded by WHO.
11. Ramsden CE, Zamora D, Leelarthaepin B, et al. (2013). Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ 346:e8707. Abstract and discussion. Recovered data from a 1966–73 trial.
12. Ramsden CE, Zamora D, Majchrzak-Hong S, et al. (2016). Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ 353:i1246. Abstract. Recovered data from a 1968–73 trial.
13. Schwingshackl L, Bogensberger B, Benčič A, Knüppel S, Boeing H, Hoffmann G (2018). Effects of oils and solid fats on blood lipids: a systematic review and network meta-analysis. J Lipid Res 59(9):1771–1782. Abstract and results. 54 trials.
14. Marklund M, Wu JHY, Imamura F, et al. (2019). Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality. Circulation 139(21):2422–2436. Abstract. 30 cohort studies; two authors report research support from Unilever for this work.
15. World Health Organization (2026). Healthy diet (fact sheet, 26 January 2026). Healthy diet: fats.
16. Sacks FM, Lichtenstein AH, Wu JHY, et al.; American Heart Association (2017). Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association. Circulation 136(3):e1–e23. Abstract.
17. Lichtenstein AH, Appel LJ, Vadiveloo M, et al. (2021). 2021 Dietary guidance to improve cardiovascular health: a scientific statement from the American Heart Association. Circulation 144(23):e472–e487. Abstract.
18. Public Authority for Food and Nutrition, Kuwait (2023). Kuwait Food-Based Dietary Guidelines (English edition). Printed pp. 23–24. Also in Arabic.
19. Supreme Council of Health, Qatar (2015). Qatar Dietary Guidelines (English edition). Printed p. 22. Also in Arabic.
20. Ministry of Health, Sultanate of Oman (2026). The Omani Guide for Healthy Eating 2026. Guideline 10. Also in Arabic.
21. World Health Organization. WHO Validation Programme for Trans Fat Elimination. Countries validated, 2023–2025 cycles.
22. الهيئة العامة للغذاء والدواء (٢٠١٩). نصائح حول سلامة زيوت القلي. In Arabic. Frying-oil safety, 10 August 2019.
23. الهيئة العامة للغذاء والدواء (٢٠١٥). كيف تختبر "الغذاء والدواء" مستوى النظافة وصلاحية الزيوت في المنشآت الغذائية؟. In Arabic. Inspectors' oil test, 12 October 2015.

Sources checked on 30 September 2026.

Log your food and training with Voltra. Free to download; the yearly plan starts with a 7-day free trial. Works fully in English and Arabic.

Related

Omega-3 and fish oil: do you need a supplement?Keto diet: does it lose more weight?Carnivore diet: what the evidence showsWhat the Gulf's official food guides say