--- topic: "Trans Fats and Margarine" title: "Trans Fats and Margarine" order: 1 description: "Where industrial trans fats still turn up, how harmful they are, and whether modern margarine or butter is the better choice for your heart." question: "Are trans fats really gone, and is margarine worse than butter?" answer: "Largely, but not entirely: modern margarine without partially hydrogenated oil is probably no worse than butter, and swapping butter for plant oils probably helps." actions: - "Read the ingredient list and skip anything containing partially hydrogenated oil, especially imported biscuits, cakes and wafers [2][6]." - "Cook and dress with liquid plant oils (olive, canola, soybean): replacing 10 g a day of butter with plant oils went with about 17% lower mortality in US cohorts [5]." - "If you prefer butter, keep it modest: each extra tablespoon a day showed small or neutral links to heart disease in pooled cohorts [11]." cautions: - "High LDL cholesterol or heart disease? Use these swaps alongside, not instead of, your clinician's plan: replacing saturated fat with unsaturated fat helps, but is one part of care [12]." - "Travelling or buying imported baked goods? Rules differ by country: in 2012–13, over half of European biscuits, cakes and wafers listing partially hydrogenated fat carried over 2% trans fat [2]." confidence: 4 confidenceNote: "Trials and cohorts agree that industrial trans fat harms the heart, but the margarine-versus-butter answer is indirect, since no large trial compares today's tub margarine with butter." evidenceSummary: rctCount: 1 observationalCount: 3 metaAnalysisCount: 4 totalParticipants: "636,000+" replicated: true newestStudyYear: 2025 references: - id: "1" url: "https://www.fda.gov/food/food-additives-petitions/trans-fat" title: "Trans Fat" authors: "U.S. Food and Drug Administration" year: 2024 journal: "FDA" - id: "2" pmid: "24844273" title: "Tracing artificial trans fat in popular foods in Europe: a market basket investigation" authors: "Stender S, Astrup A, Dyerberg J" year: 2014 journal: "BMJ Open" - id: "3" pmid: "2374566" title: "Effect of dietary trans fatty acids on high-density and low-density lipoprotein cholesterol levels in healthy subjects" authors: "Mensink RP, Katan MB" year: 1990 journal: "N Engl J Med" - id: "4" pmid: "26268692" title: "Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies" authors: "de Souza RJ, Mente A, Maroleanu A, et al." year: 2015 journal: "BMJ" - id: "5" pmid: "40048719" title: "Butter and Plant-Based Oils Intake and Mortality" authors: "Zhang Y, Chadaideh KS, Li Y, et al." year: 2025 journal: "JAMA Intern Med" - id: "6" url: "https://www.who.int/news-room/fact-sheets/detail/trans-fat" title: "Trans fat (fact sheet)" authors: "World Health Organization" year: 2024 journal: "WHO" - id: "7" pmid: "20209147" title: "Effect of animal and industrial trans fatty acids on HDL and LDL cholesterol levels in humans--a quantitative review" authors: "Brouwer IA, Wanders AJ, Katan MB" year: 2010 journal: "PLoS One" - id: "8" pmid: "19424218" title: "Health effects of trans-fatty acids: experimental and observational evidence" authors: "Mozaffarian D, Aro A, Willett WC" year: 2009 journal: "Eur J Clin Nutr" - id: "9" pmid: "28403435" title: "Hospital Admissions for Myocardial Infarction and Stroke Before and After the Trans-Fatty Acid Restrictions in New York" authors: "Brandt EJ, Myerson R, Perraillon MC, et al." year: 2017 journal: "JAMA Cardiol" - id: "10" pmid: "27422506" title: "The Increasing Use of Interesterified Lipids in the Food Supply and Their Effects on Health Parameters" authors: "Mensink RP, Sanders TA, Baer DJ, et al." year: 2016 journal: "Adv Nutr" - id: "11" pmid: "27355649" title: "Is Butter Back? A Systematic Review and Meta-Analysis of Butter Consumption and Risk of Cardiovascular Disease, Diabetes, and Total Mortality" authors: "Pimpin L, Wu JH, Haskelberg H, et al." year: 2016 journal: "PLoS One" - id: "12" pmid: "28620111" title: "Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association" authors: "Sacks FM, Lichtenstein AH, Wu JHY, et al." year: 2017 journal: "Circulation" --- Largely, but not entirely. The US removed partially hydrogenated oil, the main source of industrial trans fat, from most food by 2021 [1], but some imported baked goods elsewhere still contain it [2]. Trans fat raises "bad" LDL cholesterol and lowers "good" HDL cholesterol [3], and is tied to more heart disease and earlier death [4]. Margarine made without it is probably no worse than butter, and swapping butter for plant oils is linked to lower mortality [5]. ## How it works **What trans fat is.** Partial hydrogenation turns liquid oil into a solid fat and creates trans fatty acids. Smaller amounts occur naturally in meat and dairy from cows, sheep and goats [1][6]. In trials at equal doses, industrial and ruminant trans fat raised the LDL-to-HDL ratio by similar amounts [7], but people eat far more of the industrial kind, and in cohorts only the industrial kind was linked to heart disease [4]. **What it does.** In a randomised crossover trial of 59 adults, a diet with 10% of energy as trans fat raised LDL by 14 mg/dL and lowered HDL by 7 mg/dL compared with oleic acid, the fat in olive oil; saturated fat raised LDL by 18 mg/dL and left HDL unchanged [3]. That dose is ten times WHO's advised ceiling of under 1% of energy, which is under 2.2 g a day on a 2,000-calorie diet [6]. At lower intakes, a review estimated 20% to 32% higher risk of heart attack or coronary death for every 2% of energy from trans fat, depending on what it replaced [8]. **Is it gone?** In 2015 the FDA ruled that partially hydrogenated oil is no longer "generally recognized as safe", with a final compliance date of 1 January 2021 [1]. After New York counties restricted trans fat, hospital admissions for heart attack and stroke fell about 6% more than in comparison counties [9]. Elsewhere it depends on the country; WHO says almost half the world's people are now covered by best-practice laws [6]. Frying itself adds little, up to about 2% to 3% of the oil, compared with 25% to 45% in partially hydrogenated oil [6]. Interesterified fats, a common replacement, are not trans fats, but their long-term effects are less well studied [10]. **Margarine versus butter.** No large trial has compared today's tub margarine with butter, so the answer is indirect. Pooled cohorts found small or neutral links between butter and heart disease [11]. Trials that replaced saturated fat with polyunsaturated vegetable oil cut cardiovascular disease by about 30% [12], and in US cohorts replacing butter with liquid plant oils went with lower mortality [5]. Tub margarines made from liquid oils fit that logic, but they remain processed spreads; liquid oils such as olive or canola are the best-supported swap. See our [seed oils guide](/seed-oils/what-are-seed-oils). ## The evidence in detail ### Trans fat and the heart In the classic feeding trial, 34 women and 25 men ate three diets for three weeks each, in random order, with 10% of energy from oleic acid, trans isomers of oleic acid, or saturated fat. Compared with oleic acid, trans fat raised LDL by 0.37 mmol/L (95% CI 0.28 to 0.45) and lowered HDL by 0.17 mmol/L (0.13 to 0.20), whereas saturated fat raised LDL by 0.47 mmol/L without changing HDL [3]. A quantitative review of 39 intervention studies found each 1% of energy from industrial trans fat, replacing cis monounsaturated fat, raised the LDL-to-HDL ratio by 0.055 (95% CI 0.044 to 0.066); the figures were 0.038 (0.012 to 0.065) for ruminant trans fat, and the difference was not significant (P = 0.37) [7]. A meta-analysis of prospective cohorts found higher total trans fat intake went with higher all-cause mortality (RR 1.34, 95% CI 1.16 to 1.56), coronary death (1.28, 1.09 to 1.50) and total coronary heart disease (1.21, 1.10 to 1.33), but not stroke or type 2 diabetes. Industrial trans fat was linked to coronary events (RR 1.42, 1.05 to 1.92) while ruminant trans fat was not (0.93, 0.73 to 1.18). Certainty was moderate for coronary outcomes and low or very low for others [4]. A review also found consistent effects on inflammation markers and endothelial function [8]. ### Policy and what remains In 11 New York counties that restricted trans fat between 2007 and 2011, admissions for heart attack and stroke combined fell an extra 6.2% (95% CI 3.2% to 9.2%) three or more years later, versus similar counties without restrictions; heart attack fell 7.8% and stroke 3.6% (not significant). This was an observational pre-post comparison [9]. In Europe, a market basket study analysed 598 biscuits, cakes and wafers listing partially hydrogenated fat from 20 capitals in 2012-13: 312 had more than 2% of fat as industrial trans fat, averaging 19% in those, and 83 products in small ethnic shops in six Western European countries averaged 23% [2]. Countries differed greatly, and these samples are from 2012-13, so current levels may differ. ### Butter, plant oils and replacement The butter meta-analysis pooled 15 cohorts (636,151 people, 28,271 deaths) and found, per tablespoon (14 g) a day, RR 1.01 (1.00 to 1.03) for all-cause mortality, 1.00 (0.98 to 1.02) for cardiovascular disease and 0.96 (0.93 to 0.99) for diabetes; no trials were found [11]. Three large US cohorts (221,054 adults, up to 33 years, 50,932 deaths) found the highest butter intake carried a 15% higher mortality (HR 1.15, 1.08 to 1.22) and the highest plant-oil intake 16% lower (HR 0.84, 0.79 to 0.90); substituting 10 g a day of butter with plant oils was linked to 17% lower mortality (HR 0.83, 0.79 to 0.86) [5]. The oils studied were safflower, soybean, corn, canola and olive, not margarine. The American Heart Association summarised trials in which swapping saturated fat for polyunsaturated vegetable oil reduced cardiovascular disease by about 30%, while swapping it for refined carbohydrate did not [12]. ### Where the evidence disagrees Saturated fat was not associated with mortality or heart disease in the cohort meta-analysis, though certainty was very low, while trials support replacing it with polyunsaturated fat [4][12]. WHO treats industrial and natural trans fat as equally harmful at the same dose, and trials agree, but cohorts link only the industrial kind to heart disease, probably because ruminant intakes are much lower [4][6][7][8]. Butter shows little signal in pooled cohorts yet looks worse than plant oils when the two are compared directly, which is compatible: it is a question of what you swap it for, and both are observational findings [5][11]. Interesterified fats are an open question [10]. **Bottom line (confidence 4 of 5).** Industrial trans fat clearly harms the heart and has been removed from most US food, though pockets remain elsewhere. Margarine without partially hydrogenated oil is probably not worse than butter, and liquid plant oils are the best-supported choice for cooking and dressing.