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14 Negative Health Effects of Trans Fats

Updated March 21, 2016 · 2 Comments

trans fat danger

Initially, trans fats were thought to be a healthy alternative to animal fats because they’re unsaturated and come primarily from plant oils. However, in 1990 scientists made a startling discovery: trans fats appeared to both increase LDL (bad) cholesterol and decrease HDL (good) cholesterol. More studies over the years confirmed this. At the present time, we do know that trans fats have a very deleterious effect on heart and metabolism in general. However, our list of negative consequences may be still unaccomplished.


Hydrogenation process

Trans fats are made by a chemical process called partial hydrogenation. The purpose of hydrogenation is to solidify an oil so that it can be made to resemble butter.

During hydrogenation process, vegetable oil is reacted under pressure with hydrogen gas at 250 – 400 F for several hours in the presence of a catalyst such as nickel or platinum. Hydrogenated oils are “molecularly changed” oils. Full hydrogenation results in saturated fat only, but partial hydrogenation will lead to the formation of trans fat.

Why Trans Fats are so widely used?

The main reason oils are hydrogenated is that the hydrogenation of the oils acts as a preservative. This leads to increased shelf life and less returns or spoilage of products. Trans fats also add a certain pleasing mouth-feel and texture to foods.

However, human body has no need for these man-made fats! Adverse effects are seen even if you eat as little as 5 g of trans fat per day.

1 Cholesterol "double whammy"

While it is true that saturated fats – found in butter, cheese and beef – raise total cholesterol levels, trans fats go a step further. They not only raise total levels, but also deplete good cholesterol (HDL), which helps protect against heart disease.

Strength of evidence: A

Intake of trans fats has been consistently shown in multiple and rigorous randomized trials to have adverse effects on blood lipids, most notably on the LDL:HDL ratio. According to the meta-analysis[1] of 12 randomized, controlled trials, the consumption of trans fatty acids raises levels of low-density lipoprotein, reduces levels of high-density lipoprotein, and increases the ratio of total cholesterol to HDL cholesterol, a powerful predictor of the risk of CHD.

2 Inflammation

Trans fats increase inflammation, which is a process by which human body responds to injury. It is thought that inflammation plays a key role in the formation of fatty blockages in heart blood vessels. Trans fats scrape the inside of the blood vessels, causing inflammation. And inflammation is the environment in which cholesterol plaque can start to accumulate.

Strength of evidence: A

Inflammatory effects of trans fats have been reported in randomized, controlled trials[4-5].

In patients with established heart disease, membrane levels of trans fatty acids (a biomarker of the dietary intake of trans fats) were independently associated with activation of systemic inflammatory responses, including substantially increased levels of interleukin-6, TNF-{alpha}, TNF receptors, and monocyte chemoattractant protein[3].

3 Endothelial dysfunction & Atherosclerosis

Several studies suggest that trans fats cause endothelial dysfunction[5, 6]. A key feature of endothelial dysfunction is the inability of blood vessels to dilate fully. Endothelial dysfunction is thought to be a key event in the development of atherosclerosis. It is also associated with hypertension, coronary artery disease, chronic heart failure, diabetes, and chronic renal failure.

Strength of evidence: A

In a randomized cross-over trial[6] scientists randomly assigned 29 healthy men and women to a diet high in trans fat or in saturated fat, in which the trans fat was replaced by saturated fats. After four weeks, the subjects were crossed over to the other diet. For each subject, the researchers took four measurements of artery dilation in the arm. They found that the ability of the blood vessels to dilate was 29 percent lower in people who ate the high trans fats compared to those on the saturated fats.

4 Heart disease: multiple cardiotoxic effects

A generation ago, when cardiologists waved Americans off saturated fats like butter and beef tallow, partially hydrogenated oils became a "safe" alternative. Now, researchers have determined that trans fat can grease the way to a heart attack faster than a cup of lard.

Numerous studies have found that trans fats raise the risk of heart disease. On a per-calorie basis, trans fats appear to increase the risk of coronary heart disease more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3 percent of total energy intake)[7]. According to the comprehensive Nurses’ Health Study – the largest investigation of women and chronic disease – trans fats double the risk of heart disease in women. Alos, they cause inflammation and calcification of arterial cells, serious risk factors for coronary heart disease[29].

Strength of evidence: A/B

Evidence from randomized controlled trials indicates that consumption of trans fatty acids leads to harmful changes in serum lipids, systemic inflammation, endothelial function, and, in nonhuman primates, visceral adiposity and insulin resistance. Trans fats increase the blood levels of triglycerides as compared with the intake of other fats, increase levels of Lp(a) lipoprotein, and reduce the particle size of LDL cholesterol, each of which may further raise the risk of coronary heart disease[2]. Although these effects would be expected to increase the risk of coronary heart disease, the relation between the intake of trans fats and the incidence of coronary heart disease reported in prospective studies has been greater than that predicted by changes in serum lipid levels alone, suggesting that trans fatty acids may also influence other risk factors for coronary heart disease.

Prospective observational studies[15, 16] demonstrate strong positive associations between trans fats consumption and risk of myocardial infarction, coronary heart disease death, and sudden death. In a large, community-based case-control study (179 cases), levels of trans fatty acids in erythrocyte membranes were associated with an increase in the risk of sudden cardiac death, after adjustment for other risk factors[8].

5 Obesity trigger

Trans fat has a very powerful association with weight gain - more so than other types of fat. Diets rich in trans fat cause a redistribution of fat tissue into the abdomen and lead to a higher body weight even when the total calories are controlled.

Scientists found that every increase of one percentage point in the portion of calories from trans fats translated to a two-pound weight gain over eight years. In other words, a woman who was consuming 6% of calories from trans fat would be 12 pounds heavier after eight years than a person eating no trans fat.

Strength of evidence: B

Researchers at Wake Forest University found that trans fats increase the amount of fat around the belly[12]. They do this not just by adding new fat, but also by moving fat from other areas to the belly. A 6-year animal experiment revealed that monkeys fed a trans fat gained 7.2% of their body weight, as compared to 1.8% for monkeys on a mono-unsaturated fat diet. Computed tomography measurements in selected monkeys showed significant abdominal fat deposits in the monkeys fed trans fats. In humans, that would be enough weight gain to significantly increase risk of diabetes and heart disease.

In a Nurses’ Health Study analysis[13] of consumed unsaturated, saturated, and trans fats and weight gain over 8 years, researchers associated a weight gain of 2.3 lb with every 1% increase in percent of calories from trans fat.

A look at the 9-year waist circumference gain among >16,000 participants in the Health Professionals Follow-up Study[14] showed that “a 2% increment in energy intake from trans fats, isocalorically substituted for either polyunsaturated fats or carbohydrates, was associated with a 0.77-cm waist gain in multivariate analyses"

6 Diabetes & insulin sensitivity

Although there is some support from observational and experimental studies for the hypothesis that high intake of trans fats may increase the risk for type 2 diabetes, inconsistencies across studies and methodological problems make it premature to draw definitive conclusions at this time. Some researchers[17] speculate that the effects of trans fatty acids are not sufficient to cause diabetes, but in the presence of underlying insulin resistance may increase the probability of developing clinical disease.

Strength of evidence: C

Three prospective studies have investigated the relation between the consumption of trans fatty acids and the incidence of diabetes. Consumption of trans fat was not significantly associated with the risk of diabetes in two of these studies among male health professionals[9] and among women in Iowa[10]. However, the intake of trans fats was significantly related to the risk of diabetes among 84,941 female nurses who were followed for 16 years and in whom self-reported diabetes was validated and information on dietary intake was periodically updated[11]. After adjustment for other risk factors, trans fat intake was positively associated with the incidence of diabetes, with a risk 39 percentage points greater for the highest trans fat consumption than for the lowest.

What might account for the different results of these studies? The intake of trans fat was relatively low among the male health professionals (overall median intake was 1.3 percent of energy, equal to the median intake in the lowest quintile among the nurses). The smaller range of intake may have limited the ability to detect a difference in the risk of diabetes. In the Iowa cohort, a validation study suggested that the self-reported diagnosis of diabetes was incorrect in 36% of subjects, and diet was assessed only at baseline and may have changed over time. Misclassification of both the exposure and outcome variables would bias the results toward a null association. Alternatively, the intake of trans fat may not be an important risk factor for new-onset diabetes, and additional studies are needed.

7 Infertility

New research suggests trans fats may also increase a woman’s risk of infertility. The researchers at the Harvard School of Public Health found that women with ovulation-related fertility problems tended to eat more trans fats than fertile women. Obtaining just 2% of total energy from trans fats instead of healthier monounsaturated fats was associated with a doubled risk for this type of infertility. For someone with a 2,000 calorie diet, this level of intake could be achieved by consuming just 4 grams of trans fats a day, an amount that could be found in a single doughnut or portion of french fries.



Strength of evidence: C

A prospective cohort study[18] conducted within the Nurses Health II study of 116,671 female registered nurses who were 24 to 42 years old at inception in 1989. A subgroup of women with incident ovulatory infertility were analyzed for their dietary intake of fats and carbohydrates to determine the association between trans fat intake and ovulatory infertility. A 2% increase in energy intake from trans unsaturated fatty acids was associated with a 94% greater risk for ovulatory infertility. Adjustment for BMI, parity, oral contraceptive use, and intake of alcohol and iron produced the largest association between trans unsaturated fatty acids and ovulatory infertility. The replacement of 2% of energy from monounsaturated with trans unsaturated fatty acids was associated with more than double the risk for ovulatory infertility. Ovulatory function can be adversely affected by intake of trans unsaturated fatty acids, by the down-regulation of PPAR-gamma expression.

8 Breast milk, Fetal and Infant Development

Trans fats in the mother’s diet also contaminate their milk. Trans fats decrease the overall fat content in mother's milk[22], thus compromising the nourishment to the infant. In addition, trans fats in human milk displace essential fatty acids (such as omega-3)[19] that help the baby, and specifically the baby’s brain and nervous system, to grow and develop.

Strength of evidence: C

The offspring of lactating rats fed a diet containing partially hydrogenated vegetable oil, or trans fats, were found to have decreased heart function for the transport of glucose, as well as exhibiting signs of insulin sensitivity problems[21].

Animal studies have shown that high maternal intakes of trans fats inhibit the formation of long-chain polyunsaturated fatty acids, which are important in fetal and infant growth as well as visual and central nervous system development. Although human studies have yet to conclusively establish this association, some studies have reported an inverse relationship between cord blood levels of trans fatty acids and birth weight and height.

9 Endometriosis

Women whose diets are heavily loaded with trans fats might be more likely to develop endometriosis.

Strength of evidence: B/C

There is a small body of scientific research work on the effects of trans fats on the risk of endometriosis.
Prospective study [24] investigated the relation between dietary fat intake and the risk of endometriosis. Researchers revealed women who consume high amounts of trans fats were 48% more likely to be diagnosed with endometriosis.

10 Malabsorption of healthy oils

Essential fatty acids are converted in the body by a series of reactions to long chain polyunsaturated fatty acids, including arachidonic acid, which is essential for tissue growth and development. Trans fats compete with the essential fatty acids for the enzyme systems involved in these reactions[20, 23].

11 Memory Impairment

Recent 2014 animal study[25] has demonstrated that constant consumption of trans fats over two generations can contribute to the development of mania-like behavior, memory impairment and other neuropsychiatric conditions.

12 Aggression

Researchers at the University of California, San Diego School of Medicine have demonstrated that consumption trans fats may promote irritability and aggression[26].

13 Hyperactive behavior

Preliminar animal research suggests that prolonged consumption of trans fats may promote hyperactive behaviors[27].

14 Suppressed prostacyclin

Trans fats cause the reduction of prostacyclin production in the body, a prostaglandin that is needed to prevent blood clots in the arteries[28].

Key to grades
A Strong evidence
B Good evidence
C Unclear or conflicting evidence

Note: Conducting randomized long-term trials to test the adverse effects of trans fat intake on the incidence of cardiovascular disease or other health conditions would be unethical, given the effects of trans fats on blood cholesterol levels and inflammation.

Sources & References

  • 1. Mensink RP, Zock PL, Kester AD, Katan MB. Effects of 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 May;77(5):1146-55. PubMed
  • 2. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. N Engl J Med. 2006 Apr 13;354(15):1601-13.
  • 3. Mozaffarian D, Rimm EB, King IB, Lawler RL, McDonald GB, Levy WC. Trans fatty acids and systemic inflammation in heart failure. Am J Clin Nutr. 2004 Dec;80(6):1521-5. PubMed
  • 4. Han SN, Leka LS, Lichtenstein AH, Ausman LM, Schaefer EJ, Meydani SN. Effect of hydrogenated and saturated, relative to polyunsaturated, fat on immune and inflammatory responses of adults with moderate hypercholesterolemia. Journal of Lipid Research. 2002;43:445-452
  • 5. Baer DJ, Judd JT, Clevidence BA, Tracy RP. Fatty acids affect plasma markers of inflammation in healthy men fed controlled diets: a randomized crossover study. Am J Clin Nutr. 2004 Jun;79(6):969-73. PubMed
  • 6. de Roos NM, Bots ML, Katan MB. Replacement of saturated fatty acids by trans fatty acids lowers serum HDL cholesterol and impairs endothelial function in healthy men and women. Arteriosclerosis, Thrombosis, and Vascular Biology. 2001;21:1233-1237.
  • 7. Oh K, Hu FB, Manson JE, Stampfer MJ, Willett WC. Fat intake and risk of coronary heart disease in women: 20 years of follow-up of the Nurses’ Health Study. Am J Epidemiol. 2005 Apr 1;161(7):672-9. PubMed
  • 8. Lemaitre RN, King IB, Raghunathan TE, et al. Cell membrane trans-fatty acids and the risk of primary cardiac arrest. Circulation 2002;105:697-701.
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  • 14. Koh-Banerjee P, Chu NF, Spiegelman D, et al.: Prospective study of the association of changes in dietary intake, physical activity, alcohol consumption, and smoking with 9-y gain in waist circumference among 16,587 U.S. men. Am J Clin Nutr. 2003 Oct;78(4):719-27.
  • 15. Mozaffarian D, Abdollahi M, Campos H, Houshiarrad A, Willett WC. Consumption of trans fats and estimated effects on coronary heart disease in Iran. Eur J Clin Nutr. 2007 Aug;61(8):1004-10. PubMed
  • 16. Ascherio A, Hennekens CH, Buring JE, Master C, Stampfer MJ, Willett WC. Trans-fatty acids intake and risk of myocardial infarction. Circulation. 1994 Jan;89(1):94-101. PubMed
  • 17. Salmero’n J, Hu FB, Manson JE, et al. Dietary fat intake and risk of type 2 diabetes in women. Am J Clin Nutr. 2001 Jun;73(6):1019-26. PubMed
  • 18. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Fatty acid intakes and the risk of ovulatory infertility. Am J Clin Nutr. 2007 Jan;85(1):231-7. PubMed
  • 19. Innis SM, King DJ. Am J Clin Nutr. 1999 Sep;70(3):383-90.
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  • 21. Osso FS, Moreira AS, Teixeira MT, Pereira RO, Tavares do Carmo MG, Moura AS. Trans fatty acids in maternal milk lead to cardiac insulin resistance in adult offspring. Nutrition. 2008 Jul-Aug;24(7-8):727-32.
  • 22. Anderson NK, Beerman KA, McGuire MA, Dasgupta N, Griinari JM, Williams J, McGuire MK. J Nutr. 2005 Mar;135(3):416-21.
  • 23. Koletzko B. Trans fatty acids may impair biosynthesis of long-chain polyunsaturates and growth in man. Acta Paediatr. 1992 Apr;81(4):302-6.
  • 24. Missmer SA, Chavarro JE, Malspeis S, Bertone-Johnson ER, Hornstein MD, Spiegelman D, Barbieri RL, Willett WC, Hankinson SE. A prospective study of dietary fat consumption and endometriosis risk. Hum Reprod. 2010 Jun;25(6):1528-35. PubMed
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2 responses so far ↓

  • 1 Mark Warner // Dec 16, 2008 at 3:09 pm

    This is why we have government. They are there to protect us from profiteering persons and corporations that foist this crap on us in the name of greater profits. Trans fats need to be made illegal NOW.

  • 2 Miroslav Nikolov // Dec 16, 2008 at 4:48 pm

    Yes, this is one of the marketing tricks to sell more products. They save money and put some bad oil in the food and in the same time this oil has to be “healthy”.
    Saturated fatty acids are bad too. The sources of saturated fats are animal products.
    The best choice are mono and polynonsaturated fatty acids. The sources of them are olives, some of the fish species, Soya, walnuts.

    I suppose if we keep these fats we will be more happy with our weight.