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Trans Fatty Acids

What are trans fatty acids?

In trans fatty acids, the two hydrogen atoms near the double bonds are on the opposite sides of the molecule–what makes them straight and thus more rigid and solid–, while in the regular cis fatty acids they are on the same side, what makes them more flexible and thus liquid [1]; (Picture 1).

Trans vs cis fatty acid structure picture

Picture 1. Cis and trans fatty acid chemical structure

Natural or Ruminant Trans Fats

Natural trans fats are also called “ruminant” because they appear in the body fat and milk of the ruminant animals, mainly cows and sheep [2].

Examples of natural trans fatty acids are vaccenic and conjugated linoleic acid (CLA) [21].

Artificial, Synthetic or Industrial Trans Fats

Artificial trans fatty acids are produced by adding hydrogen–a process known as partial hydrogenation–to liquid oils; this makes them solid at room temperature, more stable during repeated deep-frying and extends their shelf time [19]. The most common synthetic trans fatty acid–elaidic acid–is produced from oleic acid (a monounsaturated fatty acid) [24]. Partially hydrogenated oils contain unsaturated, saturated and trans fats [41].

NOTE: Partial hydrogenation converts cis fatty acids into trans fatty acids, while full hydrogenation converts them into saturated fatty acids, so “partially hydrogenated” oils contain trans fatty acids while “hydrogenated” oils do not. In practice, on food ingredients lists, “hydrogenated oil” may refer to either hydrogenated or partially hydrogenated oil, though.

Foods High in Trans Fats

Synthetic or industrial trans fats can be added to various foods (Picture 2, Chart 1).

Foods High in Trans Fats Examples Picture

Picture 2. Examples of foods with added (industrial) trans fats

Chart 1. List of Common Foods High in Trans Fats


Trans fats (g)

French fries (1 serving) 0-6.1*
Vegetable shortening (1 tbsp, 13 g) 2-5.5
Breaded chicken nuggets (1 serving) 0-5*
Partially hydrogenated oil (1 tbsp, 14 g) 0.5-4.5*
Pies (1 serving) 2-4.7*
Vanaspati ghee [vegetable ghee used in South Asia] (1 tbs, 14 g) [22,23] 0.5-4
Margarine, hard (stick) (1 tbsp, 14 g) 0.5-3.5
Cheeseburger, hamburger (200-400 g) 1-3*
Pancakes (1 serving) 0.1-3
Doughnuts (1 serving) 0.1-2.7
Cake (1 piece, 144 g) 2

  • Spreads, nondairy coffee cream, salad dressings
  • Commercially baked products: biscuits, brownies, cakes, cookies, crackers, muffins
  • Deep-fried fast food products and packaged snack foods: fried chicken, microwave popcorn, potato chips, tortilla chips, granola bar
  • Candies, confectioner coating, peanut butter
  • Burrito
  • Frozen products: breaded fish sticks, cinnamon rolls, meatballs, pie crusts, pizza dough, ready-made frosting, waffles
  • Dry mixes: Cake, pancakes, mac mixes
  • Soft (tub) margarines
  • Sunflower seeds (oil roasted)
0-2 g/serving

* Some fast food chains and restaurants in the United States have stopped using trans fats, so certain foods listed in the chart as high in trans fats may actually have almost no trans fats [29]. The amount of trans fats in foods can vary greatly among brands; you may find exact data on the producers’ websites.
Sources: USDA.gov [2], The New England Journal of Medicine (data from 2002) [18]

Food Products Without Artificial Trans Fats

When producers do not use trans fats in the food processing, all their foods, including those in Chart 1, can be free of artificial trans fats. Zero trans fat French fries, potato chips, chicken nuggets, pies, margarines and shortening are available. You can usually find the amount of trans fats in foods on producers’ websites.

In the United States, food products that contain less than 0.5 g trans fat are considered trans fat free [28]. Below is a list of foods that that contain practically zero artificial and natural trans fats (<0.2 g/serving) [2]:

    • Vegetable oils: canola (non-hydrogenated version of low-erucic-acid rapeseed oil), corn, cottonseed, hazelnut, linseed, olive, peanut, rice-bran, safflower, sesame, soybean, sunflower and walnut oil (except when they are “partially hydrogenated”)
    • Coconut, palm and palm-kernel oil
    • Certain margarines and margarine-like spreads (there should be no “trans fats” on Nutrition Facts labels and no “partially hydrogenated oil” or Ingredients labels)
    • Most breakfast cereals
    • Nuts and seeds
    • Legumes
    • Fruits
    • Vegetables
    • Most candies
    • Fish and other seafood
    • Most yogurts and ice creams
    • Eggs
    • Mayonnaise
    • Milk chocolate

Are natural or ruminant trans fats harmful?

According to 3 systematic reviews (2006, 2011), there is no association between the intake of natural trans fats and coronary heart disease [12,18,21]. The potential health benefits of conjugated linolenic acid (CLA) found in milk have not been proven so far [21].

Trans fats occur naturally occur in red meat: beef, lamb and veal (up to 2 g/3 oz) and, in smaller amounts (<0.5 g/serving), in pork, poultry, cheese (American pasteurized, cheddar, mozzarella, Mexican quesadilla), milk and butter [2].

Reheating Oils and Formation of Trans Fats

In few baking and stir-frying experiments, ordinary heating of vegetable oils, like canola oil, to up to 527 °F (275 °C), did not significantly increase the amount of trans fatty acids [38,39]. It is not only heating but adding hydrogen to oils in the presence of a catalyst, like nickel, that converts cis unsaturated fats to trans fats [40].

Cooking at relatively low temperatures (325-375° F or 163-191° C) can actually spoil certain oils, such as extra virgin olive oil, but this is because of formation of free fatty acids, which have a bad taste, and not due to formation of trans fatty acids.

The Effect of Industrial Trans Fats on Blood Cholesterol Levels

Trans fats increase the blood levels of:

  • Total cholesterol [3,4-V9,6,18]
  • LDL cholesterol [3,4-V9,6,18] and small dense LDL particles [18] but probably not oxidized LDL cholesterol levels [37]
  • Total/HDL cholesterol ratio [3,6,18]
  • Triglycerides [5,18,36]
  • Lipoprotein Lp(a) [18,36]

All of the above changes in blood lipid are associated with increased risk of coronary heart disease [18].

Harmful Effects of Trans Fats

Trans Fats, Inflammation and Atherosclerosis

There is CONFLICTING EVIDENCE about the effect of trans fats on systemic inflammation: in one interventional study, trans fats increased markers of inflammation [52] but in another one did not [49]. There is another conflict in observational studies: in 2 reviews of the Nurses Health Study I, two different groups of researchers have found different markers of inflammation [53,54,55].

Based on 2 observational studies in individuals with documented atherosclerosis of the coronary arteries, there is LIMITED EVIDENCE that intake of trans fats is associated with atherosclerosis, which is the main cause of coronary heart disease [47,48].

Trans Fats and Coronary Heart Disease and Stroke

According to several studies, systematic reviews and meta analyses, high trans fat intake increases the risk of coronary heart disease:

  • According to two 2009 systematic reviews, there is convincing evidence that intake of trans fats increases the risk of coronary heart disease [16,17].
  • According to a opinion of European Food safety Authority from 2007, there is association between higher intakes of  trans fats and coronary heart disease [36].
  • According to one 2006 review of studies, an increase of trans fat intake by 2% of calorie intake (5 g trans fat in a 2,000 Cal diet) is associated with 23% increase in incidence of coronary heart disease [19].
  • According to 2 reviews (1993, 1997) of the Nurses Health Study, consumption of trans fats (margarine, biscuits, cakes, white bread) may be associated with coronary heart disease in women [14,15].
  • According to one 1999 review, trans fats increase the risk of coronary heart disease [19].

Some studies have found only weak or no association between high trans fat intake and heart disease, though:

  • According to one 2011 systematic review and meta analysis of studies, there is only small, insignificant association between intake of industrial trans fats and chronic heart disease [12].
  • In the Health Professionals Follow-Up Study (1986-1992), trans fat intake, when adjusted for dietary fiber and total fat intake, was negatively associated (0.93) with a risk of fatal coronary heart disease [9], while in one prospective Finnish study (1985-1988), trans fat intake was associated with increased risk of coronary heart disease regardless of fiber intake [57].
  • In the 1995 EURAMIC study in several European countries and Israel, trans fat intake (estimated from the trans fat content of the body fat) in men who had heart attack was not greater than in men who did not have heart attack [10].
  • In another 1995 study, individuals who have died from sudden cardiac death due to coronary heart disease did not have greater amounts of trans fats in their body fat than healthy live individuals [11].

Trans Fats and Diabetes 2

There is INSUFFICIENT EVIDENCE about trans fatty acids as a risk factor for diabetes 2 [7,8,18,36].

Trans Fats and Cancer

There is NO CONSISTENT EVIDENCE about the association between trans fat intake and cancer [31,36].

  • In one prospective study in men (1982-1995) [32], but not in another one (1994-2003) [34], trans fat intake was associated with increased risk of prostate cancer. Note, that at the time of the studies, the average trans fat consumption was much higher than today.
  • In one prospective study in women (1989-2002), trans fat intake was supposedly associated with increased risk of breast cancer [33].

Trans Fats and Other Health Risks

  • According to one 2014 systematic review of observational studies, intake of trans fats is associated with increased risk of Alzheimer disease [13].
  • According to one prospective study in married women (1991-1999), high intake of trans fats may increase the risk of ovarian infertility [35].
  • There seems to be no association between trans fat intake and allergies, high blood pressure or thrombosis [36].

How much trans fats is too much?

According to one 2006 review of studies, as low as 2 grams of trans fats per day can increase the risk of coronary heart disease [19]. American Heart Association recommends to limit trans fats to less than 1% of energy intake, that is less than 2 g of trans fats in a 2,000 Calorie diet [25]. Dietary Guidelines for Americans 2010 by US Department of Agriculture recommend avoiding trans fats as much as possible [20].

Chart 2. Difference Between Saturated, Unsaturated and Trans Fats

Fatty acids Lauric, myristic, palmitic, stearic
  • Monounsaturated: oleic, palmitoleic
  • Polyunsaturated: linoleic, alpha-linolenic
Foods Beef, pork, lamb, butter, cheese, milk; coconut, palm and palm kernel oil Vegetable oils (canola, corn, flaxseed, olive, peanut, rice bran, safflower, sesame,  soybean, sunflower), nuts, seeds Partially hydrogenated oils, margarine, Vanaspati ghee
Aggregate state at room temperature Solid (melting point of palmitic acid is ~63 °C [42]) Liquid (melting point of oleic acid is ~13 °C [27]) Solid or semi-solid (melting point of elaidic acid is ~44 °C [26])
Dangers for health Dangers not firmly proven Considered “good” fats Considered most dangerous

FDA and Trans Fats

According to the US Food and Drug Administration (FDA) regulation, all foods that contain 0.5 grams or more trans fat per serving have trans fat listed on the Nutrition Facts labels [28]. FDA has also removed trans fats and partially hydrogenated soybean and cottonseed oil from the list of Generally Recognized As Safe (GRAS) food ingredients [1,43], which means they may become illegal in the United States in near future. On the other hand, partially hydrogenated menhaden oil [1,50] and partially hydrogenated version of low-erucic-acid rapeseed oil (LEAR), known as canola oil [1,51] are still listed as GRAS.

Trans Fat Ban

In Europe, trans fats are “nearly banned” in Denmark, Austria, Hungary, Iceland, Norway and Switzerland [44]. In general, the use of trans fats in Western Europe has declined, while in Eastern Europe may still be high [30].

In the United States, in the New York City [45] and California [46], trans fats are banned in restaurants.

Related Nutrients

  1. 2013, Tentative Determination Regarding Partially Hydrogenated Oils; Request for Comments and for Scientific Data and Information  Federal Register
  2. List of foods containing trans fats  US Department of Agriculture
  3. Mensink RP et al, 2003, 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  The American Journal of Clinical Nutrition
  4. 2002, Third Report of the  National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III)  Circulation
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  6. Brouwer IA et al, 2006, Effect of Animal and Industrial Trans Fatty Acids on HDL and LDL Cholesterol Levels in Humans – A Quantitative Review  PubMed Central
  7. Odegaard AO et al, 2006, Trans fatty acids, insulin resistance, and type 2 diabetes  PubMed
  8. van Dam MR et al, 2002, Dietary fat and meat intake in relation to risk of type 2 diabetes in men  PubMed
  9. Ascherio A et al, 1996, Dietary fat and risk of coronary heart disease in men: cohort follow up study in the United States  PubMed Central
  10. Aro A et al, 1995, Adipose tissue isomeric trans fatty acids and risk of myocardial infarction in nine countries: the EURAMIC study  PubMed
  11. Roberts TL et al, 1995, Trans isomers of oleic and linoleic acids in adipose tissue and sudden cardiac death  PubMed
  12. Bendsen NT et al, 2011, Consumption of industrial and ruminant trans fatty acids and risk of coronary heart disease: a systematic review and meta-analysis of cohort studies  PubMed
  13. Barnard ND et al, 2014, Saturated and trans fats and dementia: a systematic review  Neurobiology of Aging
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  17. Mente A et al, 2009, A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease  PubMed
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  20. Dietary Guidelines For Americans 2010  US Department of Agriculture
  21. Gebauer SK et al, 2011, Effects of Ruminant trans Fatty Acids on Cardiovascular Disease and Cancer: A Comprehensive Review of Epidemiological, Clinical, and Mechanistic Studies  Advances in Nutrition
  22. 2011, Vanaspati: Desi vegetable ghee  State Consumer Helpline Knowledge Resource Management Portal (SCHKRMP)
  23. Ghafoorunissa G, 2008, Role of trans fatty acids in health and challenges to their reduction in Indian foods  PubMed
  24. Dietary Guidelines for Americans 2005, Health.gov
  25. Lichtenstein AH et al, Diet and Lifestyle Recommendations Revision 2006, A Scientific Statement From the American Heart Association Nutrition Committee  Circulation
  26. Elaidic acid  ChemSpider
  27. Oleic acid  ChemSpider
  28. 2003, Guidance for Industry: Trans Fatty Acids in Nutrition Labeling, Nutrient Content Claims, Health Claims; Small Entity Compliance Guide  US Food and Drug Administration
  29. Carrol A, 2013, Goodbye and good riddance, trans fats  CNN
  30. Stender S et al, 2012, A trans European Union difference in the decline in trans fatty acids in popular foods: a market basket investigation  BMJ Open
  31. 2012, Common questions about diet and cancer  American cancer Society
  32. Chavarro J et al, 2006, A prospective study of blood trans fatty acid levels and risk of prostate cancer  Meeting Abstracts Online
  33. Chajès V et al, 2008, Association between serum trans-monounsaturated fatty acids and breast cancer risk in the E3N-EPIC Study  PubMed Central
  34. Brasky TM et al, 2011, Serum Phospholipid Fatty Acids and Prostate Cancer Risk: Results From the Prostate Cancer Prevention Trial  PubMed Central
  35. Chavarro JE et al, 2007, Dietary fatty acid intakes and the risk of ovulatory infertility  The American Journal of Clinical Nutrition
  36. 2007, Opinion of the Scientific Panel on Dietetic products, nutrition and allergies [NDA] related to the presence of trans fatty acids in foods and the effect on human health of the consumption of trans fatty acids  European Food Safety Authority
  37. Halvorsen B et al, 1996, Effects of partially hydrogenated fish oil, partially hydrogenated soybean oil and butter on the susceptibility of low density lipoprotein to oxidative modification in men  PubMed
  38. Przybylski O et al, 2012, Formation of trans fats during food preparation  PubMed
  39. Tsuzuki W et al, 2010, Formation of trans fatty acids in edible oils during the frying and heating process  ScienceDirect
  40. About Trans Fat and Partially Hydrogenated Oils  Center for Science in the Public Interest
  41. Oil, vegetable, industrial, soy (partially hydrogenated), principal uses popcorn and flavoring vegetables  SELF NutritionData
  42. Palmitic acid  ChemSpider
  43. 2013, FDA Targets Trans Fat in Processed Foods  US Food and Drug Administration
  44. 2014, Europe leads the world in eliminating trans fats  World Health Organization, Europe
  45. Taverne S, June 16, 2015, F.D.A. Sets 2018 Deadline to Rid Foods of Trans Fats  The New York Times
  46. Gorn D, 2013, California’s Trans Fat Law Set Stage for Pending National Ban on the ‘Anti-Food  California Healthline
  47. Siquel EN et al, 1993, Trans-fatty acid patterns in patients with angiographically documented coronary artery disease  PubMed
  48. Merchant AT et al, 2008, Interrelation of saturated fat, trans fat, alcohol intake, and subclinical atherosclerosis  The American Journal of Clinical Nutrition
  49. Smit LA et al, 2011, A High Intake of trans Fatty Acids Has Little Effect on Markers of Inflammation and Oxidative Stress in Humans  The Journal of Nutrition
  50. Menhaden oil [21 CFR 184.1472(b)]  US Government Publishing Office
  51. Rapeseed oil [21 CFR 184.1555(c)(2)]  US Government Publishing Office
  52. Bendsen BT et al, 2011, Effect of industrially produced trans fat on markers of systemic inflammation: evidence from a randomized trial in women PubMed Central
  53. Mozaffarian D et al, 2004, Dietary intake of trans fatty acids and systemic inflammation in women  PubMed Central
  54. Lopez-Garcia E et al, 2005, Consumption of Trans Fatty Acids Is Related to Plasma Biomarkers of Inflammation and Endothelial Dysfunction  The Journal of Nutrition
  55. Esmaillzadeh et al, 2008, Home use of vegetable oils, markers of systemic inflammation, and endothelial dysfunction among women  The American Journal of Clinical Nutrition
  56. Oil, vegetable, canola [low erucic acid rapeseed oil]  NutritionData
  57. Pietinen P et al, 1997, Intake of Fatty Acids and Risk of Coronary Heart Disease in a Cohort of Finnish Men  American Journal of Epidemiology

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