Trans Fats: The Most Dangerous Fat in Our Food

Table of Contents

1. Key Harms at a Glance
2. What Trans Fats Are
3. The Partial Hydrogenation Process
4. How Trans Fats Were Marketed as 'Healthy'
5. Cardiovascular Disease Mechanism (Health Effects)
6. The U.S. Food and Drug Administration Ban and Its Limitations (Safety)
7. Labeling Loopholes
8. Interesterified Fats: The Replacement Concern
9. Global Bans and Restrictions Timeline
10. WHO REPLACE Framework and Elimination Target
11. Where Trans Fats Still Turn Up
12. Key Research Papers
13. Connections
14. Featured Videos

Key Harms at a Glance

• Most dangerous fat ever introduced — no known safe level of artificial trans fat consumption.
• Raises low-density lipoprotein (LDL), lowers high-density lipoprotein (HDL) — uniquely worsens cholesterol ratio more than any other dietary fat.
• Nearly doubles coronary heart disease (CHD) risk per 2% of calories — Nurses' Health Study, 14 years of follow-up (Hu 1997).
• Increases Lp(a) — independent, treatment-resistant cardiovascular risk factor.
• Promotes systemic inflammation — raises C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha.
• More than 278,000 deaths a year (World Health Organization, WHO, 2024) — attributed globally to industrially produced trans fat.
• U.S. Food and Drug Administration (FDA) delayed 25 years — evidence clear by early 1990s; no new partially hydrogenated oils (PHOs) could be added to foods after June 18, 2018, with a final compliance date of January 1, 2021.
• 0.5g 'loophole' — products with up to 0.49g/serving may still be labeled '0g trans fat'.
• Interesterified fats as replacement — inadequately tested; trial results are mixed and long-term effects are not known.

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What Trans Fats Are

• Chemical structure: Trans fats are unsaturated fatty acids that contain at least one double bond in the "trans" configuration, meaning the hydrogen atoms are on opposite sides of the carbon chain. This unnatural configuration gives the fat a straight, rigid shape similar to saturated fats
• Natural occurrence: Small amounts of natural trans fats (such as vaccenic acid and conjugated linoleic acid) are produced by bacteria in the stomachs of ruminant animals and are found in small quantities in meat and dairy. These natural trans fats appear to have neutral or even beneficial health effects. They are eaten in much smaller amounts than industrial trans fats once were, but a 2010 review of 39 feeding trials (Brouwer and colleagues) found that ruminant trans fats and conjugated linoleic acid raised the ratio of LDL to HDL cholesterol much as industrial trans fats did, with no significant difference between them; the authors concluded that all fatty acids with a trans double bond raise this ratio. The WHO trans-fat fact sheet (2024) states that industrially produced and naturally occurring trans fat are equally harmful
• Industrial trans fats: The overwhelming majority of trans fats in the food supply are artificially created through partial hydrogenation, a process that forces hydrogen gas into liquid vegetable oils under high pressure and temperature in the presence of a metal catalyst
• Properties: Partial hydrogenation transforms liquid oils into semi-solid or solid fats with a longer shelf life, higher melting point, and desirable texture for baking and frying, all at a fraction of the cost of butter or other solid fats

The Partial Hydrogenation Process

• Process overview: Liquid vegetable oil (typically soybean, cottonseed, or canola) is heated to high temperatures and exposed to hydrogen gas under high pressure in the presence of a nickel or platinum catalyst
• What happens chemically: The hydrogen atoms add to some of the double bonds in the polyunsaturated fatty acid chains, converting them from their natural "cis" configuration to the unnatural "trans" configuration
• Partial vs. full: Partial hydrogenation deliberately stops the process before completion, producing a semi-solid fat with specific texture properties. Full hydrogenation converts all double bonds to single bonds, creating a fully saturated fat that does not contain trans fats
• Byproduct of processing: Trans fats are essentially a byproduct of the partial hydrogenation process. The goal is to create a solid fat, but the trans configuration is an unavoidable consequence of the chemistry involved
• Deodorization trans fats: Even non-hydrogenated seed oils can contain small amounts of trans fats generated during the high-temperature deodorization step of refining

How Trans Fats Were Marketed as "Healthy"

• Margarine vs. butter: Beginning in the 1960s, margarine made from partially hydrogenated vegetable oils was heavily promoted as a heart-healthy alternative to butter, based on the theory that replacing saturated fat with unsaturated fat would reduce heart disease
• The first shortening: A hydrogenated vegetable shortening introduced in 1911 was the first major partially hydrogenated food product and was marketed as a modern, scientific, and healthier alternative to lard and butter
• Medical endorsements: The American Heart Association and other medical organizations recommended replacing butter with margarine and using vegetable shortening instead of animal fats, unwittingly promoting trans fat consumption
• Decades of harm: For nearly 50 years, from the 1960s through the early 2000s, Americans were actively encouraged to consume trans fats by their doctors, dietitians, and government dietary guidelines
• Industry knowledge: Internal industry documents suggest that food manufacturers were aware of potential health risks associated with trans fats long before the scientific consensus shifted, but continued to use and promote them due to their low cost and functional advantages
• Ironic reversal: The very fats that were promoted as healthy replacements for butter turned out to be far more dangerous than the saturated fats they replaced, representing one of the most catastrophic public health mistakes of the 20th century

Cardiovascular Disease Mechanism

• Raises low-density lipoprotein cholesterol: Trans fats significantly increase levels of low-density lipoprotein ("bad") cholesterol, the form of cholesterol most strongly associated with atherosclerosis and cardiovascular disease
• Lowers high-density lipoprotein cholesterol: Unlike saturated fats, which raise both low-density lipoprotein and high-density lipoprotein, trans fats simultaneously lower high-density lipoprotein ("good") cholesterol, the protective form that helps remove cholesterol from arterial walls
• Worst of both worlds: The combination of raising low-density lipoprotein and lowering high-density lipoprotein means that trans fats worsen the overall cholesterol ratio more than any other type of dietary fat, making them uniquely damaging to cardiovascular health
• Increases Lp(a): Trans fats increase levels of lipoprotein(a), an independent and particularly dangerous risk factor for heart disease that is resistant to most dietary and pharmaceutical interventions
• Promotes inflammation: Trans fats increase levels of inflammatory markers including C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), promoting systemic inflammation that damages blood vessel walls
• Endothelial dysfunction: Trans fats impair the function of the endothelium, the inner lining of blood vessels, reducing its ability to regulate blood flow, prevent clotting, and resist plaque formation
• Quantified risk: In the Nurses' Health Study (80,082 women followed for 14 years; Hu and colleagues, 1997), each 2% of calories from trans fat, in place of the same calories from carbohydrates, was linked to a nearly doubled risk of coronary heart disease (relative risk 1.93). The 20-year follow-up (Oh and colleagues, 2005) found a 33% higher risk in women with the highest versus the lowest trans-fat intake
• Replacement estimate: The same 1997 analysis estimated that replacing 2% of calories from trans fat with unhydrogenated unsaturated fats would lower coronary heart disease risk by about 53% (95% confidence interval 34–67%)
• Death toll: The U.S. Centers for Disease Control and Prevention (CDC) estimated that eliminating artificial trans fats from the U.S. food supply could prevent 10,000 to 20,000 heart attacks and 3,000 to 7,000 coronary heart disease deaths annually

The U.S. Food and Drug Administration Ban and Its Limitations

• 2006 labeling requirement: The U.S. Food and Drug Administration first required trans fat content to be listed on Nutrition Facts labels in 2006, leading to voluntary reformulation by many food manufacturers
• 2015 determination: The U.S. Food and Drug Administration determined that partially hydrogenated oils (PHOs) are no longer "Generally Recognized as Safe" (GRAS) for use in human food
• 2018 and 2021 deadlines: For most uses, June 18, 2018 was the date after which manufacturers could not add partially hydrogenated oils to foods. To let products already made work their way through distribution, the U.S. Food and Drug Administration extended the final compliance date to January 1, 2021 — after decades of documented harm and hundreds of thousands of preventable deaths
• 2023 clean-up: In 2023 the U.S. Food and Drug Administration issued a direct final rule removing outdated references to partially hydrogenated oils from its regulations
• Delayed action: The scientific evidence linking trans fats to heart disease was strong by the early 1990s, meaning the U.S. Food and Drug Administration took over 25 years to act, during which time trans fats continued to cause preventable deaths
• Industry lobbying: Food industry lobbying was a significant factor in delaying regulatory action against trans fats, with manufacturers arguing that reformulation would be too costly and that consumers should be allowed to make their own choices

Labeling Loopholes

• The 0.5 gram loophole: U.S. Food and Drug Administration regulations allow products containing less than 0.5 grams of trans fat per serving to be labeled as containing "0 grams" of trans fat, effectively hiding the presence of trans fats from consumers
• Manipulated serving sizes: Some manufacturers reduced their stated serving sizes to bring the trans fat content per serving below the 0.5 gram threshold, allowing a "0g trans fat" label on products that still contain significant amounts
• Cumulative exposure: A consumer eating multiple servings or multiple products each containing up to 0.49 grams of trans fat labeled as "0g" could easily consume several grams of trans fat daily without knowing it
• The ingredient list: "Partially hydrogenated" oils in the ingredient list are the one reliable sign of hidden trans fats; they indicate trans fats regardless of what the Nutrition Facts label says
• Post-ban residual: Even after the 2018 ban, some products may still contain trace amounts of trans fats from the deodorization process of refined seed oils and from other processing steps

Interesterified Fats: The Replacement Concern

• What they are: As trans fats were phased out, food manufacturers increasingly turned to interesterified fats, which are produced by rearranging the fatty acid positions on the glycerol backbone of fat molecules using chemical catalysts or enzymes
• Purpose: Interesterification allows manufacturers to create solid or semi-solid fats from liquid oils without producing trans fats, providing the same functional properties that partially hydrogenated oils once delivered
• Limited safety data: Despite their widespread adoption as trans fat replacements, interesterified fats have undergone far less safety testing than the trans fats they replaced
• Early concerns: Preliminary research suggests that interesterified fats may adversely affect blood glucose metabolism, insulin response, and high-density lipoprotein cholesterol levels, raising questions about whether they are truly a safe alternative
• The 2007 trial: In a 30-person crossover study of 4-week whole-food diets (Sundram and colleagues), a stearic acid-rich interesterified fat and a trans-rich partially hydrogenated soybean oil both raised the LDL-to-HDL cholesterol ratio and fasting blood sugar compared with palm olein; fasting blood sugar rose almost 20% on the interesterified fat, and in 19 participants the rise in blood sugar after an interesterified-fat test meal was 40% greater than after the other test meals
• Later trials: An 8-week trial in 85 healthy overweight adults (Ng and colleagues, 2018) found no difference in markers of insulin resistance between two chemically interesterified fats and natural palm olein. A 2025 crossover trial in which 47 healthy adults completed 6 weeks on each of two interesterified fats at 10% of calories (Hall and colleagues) found no difference between the palmitic acid-rich and stearic acid-rich fats in the total-to-HDL cholesterol ratio or other heart and metabolic risk markers; the authors note that long-term effects could not be determined
• Open questions: A 2016 expert workshop (Mensink and colleagues) concluded that interesterified fats are a feasible replacement for trans fats, but that questions remain about their effects on parts of fat and sugar metabolism, inflammation, blood clotting and fullness after eating
• No labeling requirement: Unlike trans fats, interesterified fats are not required to be listed on nutrition labels, making it difficult for consumers to know when they are consuming them
• Repeating history: Critics warn that the rush to adopt interesterified fats without thorough long-term safety testing mirrors the same pattern that led to decades of harm from trans fats

Global Bans and Restrictions Timeline

• Denmark (2003): Became the first country to effectively ban artificial trans fats by limiting them to no more than 2% of total fat in all food products, a policy that led to measurable reductions in cardiovascular deaths
• Switzerland (2008): Adopted limits on trans fats in food products similar to Denmark's regulations
• Austria, Hungary, Iceland, Norway, Sweden: Implemented trans fat restrictions or bans following Denmark's successful model
• New York City (2006): Became the first major U.S. city to ban artificial trans fats in restaurant food, with other cities following suit
• California (2008): First U.S. state to ban trans fats in restaurant cooking
• Canada (2018): Banned partially hydrogenated oils in all food sold in Canada
• United States (2018–2021): U.S. Food and Drug Administration bar on adding partially hydrogenated oils to foods from June 18, 2018, with a final compliance date of January 1, 2021
• Thailand (2019): Banned the production, import, and sale of partially hydrogenated oils
• India (2022): Implemented a limit of 2% trans fat in oils and fats
• Brazil, Singapore, Saudi Arabia: Have implemented various restrictions on trans fat content in food products

WHO REPLACE Framework and Elimination Target

• Global target: In 2018, the World Health Organization launched the REPLACE action framework with the goal of eliminating industrially produced trans fats from the global food supply by 2023
• REPLACE components: The framework outlines six strategic actions: Review dietary sources, Promote replacement with healthier fats, Legislate regulations, Assess and monitor, Create awareness, and Enforce compliance
• Progress report: The WHO fact sheet of 24 January 2024 states that almost half of the world's population is covered by best-practice policies for eliminating trans fat. Since April 2023 a WHO validation programme formally recognizes countries that have eliminated industrially produced trans fat from their food supply
• Ongoing harm: The World Health Organization's 2024 fact sheet states that more than 278,000 deaths each year globally can be attributed to intake of industrially produced trans fat
• Economic argument: The World Health Organization estimates that eliminating trans fats would save billions of dollars in healthcare costs annually and is one of the most cost-effective public health interventions available
• Inequitable burden: The health burden of trans fats falls disproportionately on low- and middle-income countries where regulations are weakest and processed food consumption is rapidly increasing

Where Trans Fats Still Turn Up

• Ingredient lists: When "partially hydrogenated" appears in the ingredient list of a packaged food, the product contains trans fats regardless of what the nutrition label claims
• "0g trans fat" labels: Products can contain up to 0.49 grams per serving and still be labeled as zero; the ingredient list shows what the label does not
• Margarine: Margarine may still contain trace amounts of trans fats or interesterified fats. Butter, ghee and olive oil are traditional fats made without partial hydrogenation (butter and ghee carry the small amounts of natural ruminant trans fat found in dairy)
• Processed baked goods: Commercially produced cookies, cakes, pastries, pie crusts, and biscuits were historically among the highest sources of trans fats and may still contain them or their replacements
• Fried foods: Deep-fried foods from restaurants may be cooked in oils that develop trans fats through repeated heating at high temperatures
• Whole foods: A diet based on whole, unprocessed foods contains no artificial trans fats and none of their questionable replacements

Key Research Papers

Key peer-reviewed research and authoritative sources underpinning the claims on this page. Links resolve to DOI, PubMed, or the issuing agency.

1. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. N Engl J Med. 2006;354(15):1601-1613. — doi:10.1056/NEJMra054035
2. Oh K, Hu FB, Manson JE, Stampfer MJ, Willett WC. Dietary fat intake and risk of coronary heart disease in women: 20 years of follow-up of the Nurses' Health Study. Am J Epidemiol. 2005;161(7):672-679. — doi:10.1093/aje/kwi085
3. Mensink RP, Zock PL, Kester AD, Katan MB. Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials. Am J Clin Nutr. 2003;77(5):1146-1155. — doi:10.1093/ajcn/77.5.1146
4. Restrepo BJ, Rieger M. Denmark's policy on artificial trans fat and cardiovascular disease. Am J Prev Med. 2016;50(1):69-76. — doi:10.1016/j.amepre.2015.06.018
5. World Health Organization. REPLACE trans fat: an action package to eliminate industrially produced trans-fatty acids. Geneva: WHO; 2018. www.who.int
6. Brouwer IA, Wanders AJ, Katan MB. Effect of animal and industrial trans fatty acids on HDL and LDL cholesterol levels in humans — a quantitative review. PLoS One. 2010;5(3):e9434. — doi:10.1371/journal.pone.0009434
7. de Souza RJ, Mente A, Maroleanu A, et al. 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. BMJ. 2015;351:h3978. — doi:10.1136/bmj.h3978
8. US Food and Drug Administration. Final determination regarding partially hydrogenated oils. Federal Register. 2015;80(116):34650-34670. www.federalregister.gov
9. Kris-Etherton PM, Lefevre M, Mensink RP, et al. Trans fatty acid intakes and food sources in the US population: NHANES 1999-2002. Lipids. 2012;47(10):931-940. — doi:10.1007/s11745-012-3704-z
10. Downs SM, Thow AM, Leeder SR. The effectiveness of policies for reducing dietary trans fat: a systematic review of the evidence. Bull World Health Organ. 2013;91(4):262-269H. — doi:10.2471/BLT.12.111468
11. Sundram K, Karupaiah T, Hayes KC. Stearic acid-rich interesterified fat and trans-rich fat raise the LDL/HDL ratio and plasma glucose relative to palm olein in humans. Nutr Metab. 2007;4:3. — doi:10.1186/1743-7075-4-3
12. Hu FB, Stampfer MJ, Manson JE, et al. Dietary fat intake and the risk of coronary heart disease in women. N Engl J Med. 1997;337(21):1491-1499. — PubMed PMID: 9366580
13. Ng YT, Voon PT, Ng TKW, et al. Interesterified palm olein (IEPalm) and interesterified stearic acid-rich fat blend (IEStear) have no adverse effects on insulin resistance: a randomized control trial. Nutrients. 2018;10(8):1112. — PubMed PMID: 30126103
14. Hall WL, Wood E, Joris PJ, et al. The effects of consumption of interesterified fats rich in palmitic acid compared with stearic acid on intermediary markers of cardiometabolic disease risk: a randomized controlled trial in healthy adults. Am J Clin Nutr. 2025;122(5):1361-1373. — PubMed PMID: 40975239
15. Mensink RP, Sanders TA, Baer DJ, et al. The increasing use of interesterified lipids in the food supply and their effects on health parameters. Adv Nutr. 2016;7(4):719-729. — PubMed PMID: 27422506
16. US Food and Drug Administration. Trans Fat (partially hydrogenated oils: 2015 determination, 2018 and 2021 compliance dates). www.fda.gov
17. World Health Organization. Trans fat (fact sheet), 24 January 2024. www.who.int
18. PubMed — search for recent research

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Connections

• All Toxins
• Cardiovascular Disease
• Seed Oils
• Atherosclerosis
• Processed Oils
• Food Additives
• Banned Additives
• Ultra Processed Foods
• Stroke
• Inflammatory Markers
• Full Body Magnetic Resonance Imaging
• Insulin Resistance
• Olive Oil
• TBHQ
• BHA and BHT
• Vitamin E
• BHA
• BHT

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