Nutrition Myths
Why are trans fats harmful?


  • Industrially produced trans fats (iTAFs) are some of the most harmful components in foods and negatively affect your health.
  • On the other hand, ruminant fats are considered safe.
  • iTFAs affect the cardiovascular health, and are also associated with inflammation, pregnancy and fetal development issues, insulin resistance and type 2 diabetes in obese people, men’s fertility and infant health problems.

Why are trans fats harmful?

There are two types of trans fats: the naturally occurring trans fats, found in milk and other dairy products and meats of ruminant animals (rTFA) and the industrially created trans fats (iTFA). The two differ structurally and have different functions in the body.

Studies show that rTFAs are safe to consume in the naturally occurring amounts (read more..). By contrast, there is strong evidence indicating that iTFAs cause many negative health problems.

The World Health Organization (WHO) recommends that TFAs in our diet should not exceed 1% of the total daily energy intake.

Since one gram of fat is equivalent to nine calories, for an average 2000 calorie diet no more than 2.2 grams should come from trans fats.

Naturally occurring TFAs (rTFAs) are excluded from these recommendations. The recommendations refer to iTFAs, which are unnaturally produced fats, mainly through a process called partial hydrogenation.

This process damages the fats during processing at high temperature and pressure.

In 2006, a large meta-analysis study showed that the risk of suffering from coronary artery disease jumped by 23% with an average daily intake of 5g of iTFAs. (1)

Many customers in countries with no iTFA restrictions consume, on average, 3-6g daily, including Vaccenic acid which is still not proven to be safe in large quantities.

These amounts may be much higher depending on the foods consumed.

So why trans fat are bad for you?

The following is a list of the known negative health effects of consuming iTFAs in amounts above the daily recommendation (1% of total energy intake):

  • Coronary heart disease (CHD)

    One of the most studied effects of a diet high in trans fats is the increased risk of developing coronary heart diseases (CHD). There are various risk factors of CHD and many of them are enhanced by the consumption of trans fats. (2, 3, 4)

    – Cholesterol levels

    iTFAs cause an increase of the total cholesterol, and a decrease of HDL (good) cholesterol. Therefore, the ratio of total cholesterol to HDL cholesterol increases. (5, 6)

    iTFAs also increase the levels of Apolipoprotein B and the ratio of ApoB/ApoA1 (a risk factor of CHD). (read more..) (7, 8)

    – Inflammation

    Inflammation is a risk factor for many diseases, including atherosclerosis, cardiovascular disease, diabetes and cancer.

    There is strong evidence that iTFAs cause an increase in the production of the inflammatory cytokines, C-reactive protein, Interleukin-6, soluble tumor necrosis factor 2, E-selectin and soluble cell adhesion molecules. (9, 10, 11, 12, 13)

    – Endothelial dysfunction

    Trans fats damage the inner lining of the blood vessels. Since trans fats get incorporated into the cell membranes of the blood vessels, they can alter the other cellular components that interact with the cell membrane wall. This can affect vascular tone/vasodilation, increase the adhesiveness of white blood cells and increase cytokine and growth factor production. (14, 15)

    – Triglycerides

    iTFAs cause an increase in blood triglycerides and triglyceride to HDL ratio – an important factor in atherosclerosis. (16, 17)

    – Omega-3

    Trans fats interfere with the metabolism of omega-3 fatty acids and, therefore, contribute to inflammation and atherosclerosis. They also cause the displacement of essential fatty acids from cell (18)

    – Insulin resistance

    Trans fats may increase insulin resistance, which affects heart health and type 2 diabetes. However, more studies are needed. See below under type 2 diabetes.

    – Prostacyclin

    Trans fats suppress the production of prostacyclin – a substance that prevents thrombosis and, therefore, is protective against heart disease. (19)

  • Obesity

    Animal studies found a possible link between trans fatty acids and central obesity, although more studies are needed on humans. (20)

  • Type 2 Diabetes

    While ruminant trans fats (rTFAs) are associated with the risk reduction of developing type 2 diabetes, studies on this association with iTFAs are mixed. Studies on animals show clear links between iTFAs and insulin resistance, (20, 21) while studies on humans are contradictory.

    Some studies show that iTFAs may increase insulin resistance, associated with obese people. It is thought that insulin resistance may occur due to iTFAs’ interference with the insulin receptors located on the cells’ membranes.

    Insulin resistance may lead to type 2 diabetes. However, more studies are needed. (22, 4, 23, 24, 25)

    Inflammation, also a risk factor of developing type 2 diabetes, has a strong association with trans-fat intake. (26, 13)

  • Pregnancy

    Trans fats may have a few pregnancy-related effects:

    May shorten the pregnancy period (27)
    May increase the risk of preeclampsia (28)
    May affect fetal development – observational studies that show that iTFAs may have harmful effects on the development of the fetus. (29)

  • Infant health

    iTFAs causes disorders on the nervous system and vision in infants. (27)

  • Men’s fertility

    Trans fats affect men’s fertility, since they interfere with the enzymes involved during sex hormone production. This results in a decreased testosterone, abnormal sperm production, motility and prostate disease. (30)

  • Cancers

    Studies on the trans fat effects on cancers are weak or inconsistent. The association is currently being researched on breast, colorectal, pancreatic and prostate cancers.

    Trans fats have an impact on cancer promoting factors in the body, primarily those related to inflammation and oxidative stress.

    They interfere with enzymes that fight cancer, damage the endothelium of blood vessels, have an impact on the C-reactive protein, Interleukin-6, Soluble tumor necrosis factor 2, E-selectin and soluble cell adhesion molecules.

    Although trans fats have not been clearly linked to cancer, there are some studies that suggest this possibility. (31, 15, 32, 33, 34, 35)

  • Allergy

    Trans fats have possible links to allergy reactions. There is evidence that consuming margarine increases the risk for eczema and allergic sensitization in children. However, it is not clear if these reactions are specific to trans fats. (36, 34)

  • Other

    There are mixed results for the following associations: macular degeneration, dementia, asthma and eczema. More studies are needed. (37)

Related Posts

Trans fat foods you need to avoid Find out how to reduce your chances of consuming trans fats and which foods you need to avoid.
How to identify trans fats on a food label? Familiarize yourself with the labeling laws in your country and learn how to identify hidden trans fats.
Does frying in oil produce trans fats? Stir frying increases the amount of trans fats, more than any other method. Deep frying in high temperatures in reused oils also, also produces trans fats.
What is trans fat? Trans fats come from 3 sources: generated through partial hydrogenation; consequence of some cooking methods; from dairy and meat of ruminant animals.
What is fat? This article discusses the different definitions of fat, making it clearer for you next time you read about fat, oil, lipids, triglycerides or adipose tissue.

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