What is trans fat?


  • There are 2 types of trans fats: industrially produced and naturally occurring in meat and dairy from ruminant animals.
  • Ruminant trans fat is consumed in small amounts and is considered as safe .
  • Trans fatty acids are damaged fat molecules that are detrimental to health.
  • Most are produced by partial hydrogenation of oils, but are also by-products of some cooking methods.
  • Trans fat rich PHOs became common in 1920s, peaked in 1980s and from 2000s were banned in some countries.
  • Not all countries plan to ban, or even introduce compulsory labelling of trans fats and PHOs. (e.g. Australia and New Zealand)
  • Trans fat increases the risk of coronary heart disease, causes inflammation, increase in blood cholesterol and triglycerides, damages blood vessels, interferes with infant health, men’s fertility and with omega 3 fatty acids metabolism.
  • Trans fat may also increase insulin resistance, risk of cancer, type 2 Diabetes, may be unsafe in pregnancy and may lead to obesity.
  • Trans fat is also linked to macular degeneration, dementia, asthma and eczema (but more studies are needed).
  • While it is safe to consume fats without fear of exceeding trans fat intake in countries with a total ban of these substances, you have no such guarantee in countries that only apply labelling restrictions or count on a voluntary trans-fat reduction.
  • In this case, the safest way to ensure a minimal intake of iTFAs is by avoiding processed foods that contain fat, and cook whole foods and non-processed ingredients.
  • Familiarizing yourself with the labels and labelling legislation in your country, is also helpful.


What is trans fat? Why are trans fats bad for you?

Trans fat: once considered a healthy alternative to butter, now banned in many countries. Find out what is trans fat, its history, what types and sources of trans fat are there, what damage to health it causes and what is the most effective method of erradicating it.

Types of trans fats

There are two types of trans fats which differ structurally and have different functions in the body:

  • the naturally occurring trans fats, found in milk and other dairy products and meats of ruminant animals. These are referred to as ruminant trans fats or ruminant trans fatty acids (rTFA). Studies show that rTFAs are safe to consume in the naturally occurring amounts.
  • the industrially created trans fats called industrial trans fatty acids (iTFA). By contrast, there is strong evidence indicating that iTFAs cause many negative health problems.

Industrial Trans fatty acids (iTFAs) have been used in processed foods for over a century. For the last four decades, strong evidence has started to show that trans fat is detrimental to our health.

However, only in the last decade, have a small number of countries started to undertake steps to reduce or eliminate iTFAs from our diets.

This article discusses industrially produced trans fat, their history, what damage they do to our bodies, and the most effective methods for eradicating them from the supermarket shelves and from our diets.


  • There are two types of trans fat with slightly different structure and effects on the body: industrial trans fat and ruminant trans fat.

What is trans fat?

This article focuses on industrial trans fatty acids since they have a significant impact in our health. Natural trans fat from ruminants are covered in another article.

In general, iTFAs can be thought of as damaged fats.

The iTFAs mainly consist of stearic, oleic and elaidic acids which melt at 108 Fahrenheit (42 degrees Celsius) and are, therefore, solid at room temperature and inside the human body.

Trans fatty acids are straight chains of carbon and hydrogen molecules that can align closely together, mimicking saturated fats. This tight alignment increases the melting point. (1)

iTFAs have a slightly different chemical structure compared to naturally occurring trans fatty acids (rTFAs). This difference is thought to exert different effects on our body.

Studies on rTFAs are very limited.  There is currently not enough knowledge to clearly pinpoint the differences in the health effects when measured gram for gram. Available studies didn’t find any evidence between rTFAs and negative health effects.

It is even believed that they might have a positive effect on health.

However, there are numerous studies on iTFAs . They show a clear link to cardiovascular diseases, cancers and other serious health issues.


  • iTFAs are damaged fats with chemical structure is similar to saturated fats.
  • There are many studies showing negative health effects of iTFAs.
  • Studies on rTFAs are limited, and there is no evidence of negative health effects if consumed in normal amounts.

Sources of trans fat

Trans fat comes mainly from 3 sources:

  • iTFAs can be generated through a process called partial hydrogenation. Most of the trans fatty acids in our diet have this origin. The largest amounts of iTFAs are found in vegetables spreads, shortenings and baked products that use PHOs.

    For a comprehensive list of foods that contain high amounts of iTFAs, please read the article Trans fat foods you need to avoid.

  • Stir frying and repeated deep frying in high temperatures also generates some trans fats, but in comparatively  very small quantities, although it may add to our daily intake of trans fat. The amount of iTFAs that originate through this method fall within the safe recommended limits.
  • Trans fat naturally occurs in milk and other dairy products and the meat of ruminant animals, but are considered safe in the amounts naturally found in these foods.


  • There are three main sources of trans fat: product of  partial hydrogenation, ruminant animal products and cooking in high temperatures.
  • The largest amounts of trans fats are in vegetable spreads, shorenings and baked products that use PHOs.

Short history of industrial trans fat

iTFAs didn’t exist, or existed only in trace amounts, in foods before the invention of partial hydrogenation in the early 1900s.

During the 1920s, partial hydrogenated oils (PHOs) became a common component of frying fats, margarines and shortenings.

The consumption of iTFAs started to increase after World War II and reached its peak in the 1970sand 1980s, when margarines were advertised as a healthier alternative to saturated-fat butter. (2)

The concerns of their health effects started soon after iTFAs invention. However, solid scientific evidence only started to emerge about four decades ago.

In the 1990s, it was shown that iTFAs increase LDL cholesterol and decrease HDL cholesterol. (3)

In Denmark, iTFAs almost disappeared after 2003/2004, when a total ban was introduced. Some European countries also introduced a total ban, after Denmark’s success in eradicating them.

The consumption of trans fat in the United States dropped drastically after the introduction of compulsory labelling. In 2016, it was estimated that there was an average consumption of 1g per day (0.5% of the daily energy intake). PHOs will be totally phased out by 2018. (4)

There are relatively few countries with bans on iTFAs and PHOs or with labelling laws that impose the disclosure of all components. In other countries, where consumers are health conscious and where manufacturers voluntarily reduce these fats, it is expected that trans fat will effectively disappear from foods.

However, in countries where the voluntary reduction doesn’t work (such as the Balkan countries), an increase of iTFAs is noted in the products. (read more..)


  • During 1920s trans fats in a form of PHOs became common in a production of frying fats, margarines and shortenings.
  • The production of iTFAs increased after World War II and peaked in 1970s and 1980s.
  • In 1990s it was shown that iTFAs increase blood cholesterol.
  • In 2000s a few European countries banned it which resulted in almost complete eradication of trans fats.
  • In the United States PHOs will be totally phased out in 2018.
  • Some countries still have no plans to introduce laws against production of trans fat.

Why are trans fats bad for you? Trans fat side effects.

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):

Trans fat increases the risk of Coronary Heart Disease

One of the most studied effects of a diet high in trans fats is the increased risk of developing coronary heart disease (CHD).

There are various risk factors of CHD and many of them are enhanced by the consumption of trans fats. (5, 6, 7)

Trans fat rises Blood 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. (8, 9)

iTFAs also increase the levels of Apolipoprotein B and the ratio of ApoB/ApoA1 (a risk factor of CHD). (10, 11)

Trans fat causes 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. (12, 13, 14, 15, 16)

Trans fat damages Blood Vessels

Trans fats damage the inner lining of the blood vessels and causes endothelial dysfunction. 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. (17, 18)

Trans fat increases blood Triglycerides

iTFAs cause an increase in blood triglycerides and triglyceride to HDL ratio – an important factor in atherosclerosis. (19, 20)

Trans fat interferes with 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 (21)

Trans fat may increase Insulin Resistance

Trans fats may increase insulin resistance, which affects heart health and type 2 diabetes. However, more studies are needed. (see section on Diabetes below)

Trans fat suppresses protection of heart disease

Trans fats suppress the production of prostacyclin – a substance that prevents thrombosis and, therefore, is protective against heart disease. (22)

Trans fat may lead to Obesity

Animal studies found a possible link between trans fatty acids and central obesity, although more studies are needed on humans. (23)

Trans fat may increase the risk of 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, (23, 24) 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. (25, 7, 26, 27, 28)

Inflammation, also a risk factor, and has a strong association with trans-fat intake. (29, 16)

Additionally, cooking in high temperatures produces trans fats and is associated with an increased risk of type 2 diabetes.

Trans fat may be harmful in Pregnancy

Trans fats may have a few pregnancy-related effects:

May shorten the pregnancy period (30)
May increase the risk of preeclampsia (31)
May affect fetal development – observational studies that show that iTFAs may have harmful effects on the development of the fetus. (32)

Trans fat affects Infant Health

iTFAs causes disorders on the nervous system and vision in infants. (30)

Trans fat interferes with 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. (33)

Trans fat may cause 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. (34, 18, 35, 36, 37, 38)

Trans fat may cause 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. (39, 37)

Other effects of trans fat

There are mixed results for the following associations: macular degeneration, dementia, asthma and eczema. More studies are needed. (40)

PHOs and Trans Fat Ban – does it work?

A ban on industrial trans-fat usage is the most effective method of insuring that these substances are not posing health risks in our society.

Various countries have introduced different methods to reduce trans fat such as: (41)

  • Compulsory labelling of packaged goods, including information on the trans fat or partially hydrogenated oil contents to enable the public to make informed choices
  • Engaging manufacturers to voluntarily change their food processing methods
  • Imposing trans-fat and/or PHO bans

Compulsory labelling

Compulsory labelling for iTFOs and PHOs is somewhat, but not 100%, effective in restricting trans fat from our diet. Many customers are not familiar with the terminology used on the labels or on the ingredients list and some labelling laws have loopholes, allowing manufacturers to conceal the real iTFOs and PHOs contents. (read more..)

Voluntary changes in food production

In some countries, the government encourages manufacturers to reduce or eliminate the production of partially hydrogenated oils and assumes society’s pressure that will occur naturally.

While some in countries PHOs usage has been reduced successfully (e.g. Australia, NZ, Germany and UK) (41), this method doesn’t seem to work in other countries (e.g. Serbia, Croatia, Bosnia and Hercegovina). Voluntary reduction initiatives seem to work, but not in all the countries that have adopted it.

Please note, however, that without enforced restrictions, there are no guarantees that the foods you eat don’t contain high amounts of iTFAs. (42)

Ban on using trans fat and PHOs

A total ban on PHOs and strict restrictions of iTFAs, insure that we can safely consume any products without exceeding the safe levels of these substances.

In some countries, such as Denmark, Switzerland, Austria, Iceland, Hungary and Norway, PHOs are not allowed in foods and a limit of 2g of iTFA per 100g of fat is applied. In the United States, the use of partially hydrogenated fats and oils will be phased out completely in 2018. (4)

The amounts of trans fat are often very high in the most popular junk food snacks, making them even more unhealthy.

The following example shows how much iTFAs are consumed from three popular junk foods. The study was done in 2008 and presents the trans fatty contents used in different countries. (32)

At the bottom of the graph, it is clear that there was a reduction in trans-fat contents in these products after Denmark applied a ban in 2003/2004.

Fortunately, in the United State, the PHOs will disappear after 2018 due to legislation introduced in 2015 to phase them out completely. This, unfortunately, cannot be said about Australia, New Zealand and many other countries which don’t plan any restrictions of iTFAs.

Contents of trans fats in common junk food

It is not surprising that the elimination of trans fat from foods, corresponded with a significant reduction in the mortality rates related to cardiovascular diseases (CDV).

Every year, since the ban in Denmark, there are on average 14.2 less deaths per 100,000 people caused by CDV. (10)

The following graph presents the reduction in the mortality rates of coronary artery disease. Although is not a proof that the mortality reduction is exclusively due to the ban on trans fat, it certainly played an important role. (42)

Mortality rate of coronary artery disease by country

Australia and New Zealand

Countries, such as Australia and New Zealand, don’t plan to implement a ban or impose any restrictions on iTFAs or PHOs use.  This is due to fear that manufacturers will replace trans fat with other harmful ingredients, such as more sugar, making matters worse.

Lab tests were performed on food samples from supermarkets. Based on this information, the consumption of trans fatty acids in Australia is estimated to be 0.5-0.6% of the total energy intake, which is below the recommended limit. (41)

Please note, however, that this does not guarantee that all products are safe to eat.  Manufacturers are not legally obliged to limit iTFAs in their foods.

This means that if you are unlucky with your choices, you might be potentially far exceeding the daily safe limits of trans fat.


  • Compulsory labelling for iTFOs and PHOs is not completely effective since it allows manufacturers to conceal the real trans fat and PHO contents.
  • Voluntary reductions work in some countries but not others. There are no guarantees that the foods you eat don’t contain high amounts of iTFAs.
  • A total ban on PHOs and strict restrictions of iTFAs, insure that we can safely consume any products without exceeding the safe levels of these substances.
  • Some countries such as Australia and New Zealand don’t protect its customers against trans fats.


You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.


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