Trans fats are a type of unsaturated fat that come in two forms: natural from ruminant animals and artificial. Natural trans fats are safe in moderation, but artificial ones may lead to health issues.

You may have heard a lot about trans fats.

These fats are notoriously unhealthy, but you may not know why.

Intake of these fats has declined in recent years related to consumer awareness and because regulators, such as the U.S. Food and Drug Administration have banned the use of industrial trans fats in commercially produced food items.

Many other countries have not yet adopted policies limiting or banning their use.

This article explains everything you need to know about trans fats.

Trans fats, or trans-fatty acids, are a form of unsaturated fat.

They come in both natural and artificial forms.

Natural, or ruminant, trans fats occur in the meat and dairy from ruminant animals, such as cattle, sheep, and goats. They form naturally when bacteria in these animals’ stomachs digest grass.

However, dairy and meat eaters needn’t be concerned.

Several reviews have concluded that a moderate intake of these fats does not appear harmful (1).

The best-known ruminant trans fat is conjugated linoleic acid (CLA), which is found in dairy foods, butter, lamb and beef.

Some food manufacturers are fortifying foods with extra CLA and marketing them as fuctional foods. There is not enough evidence in humans yet to support the use of CLA supplements or these fortified foods marketed as functional or medical foods (2).

However, artificial trans fats — otherwise known as industrial trans fats or partially hydrogenated fats — are hazardous to your health.

These fats occur when vegetable oils are chemically altered to stay solid at room temperature, which gives them a much longer shelf life (3).


Trans fats are found in two forms — natural, which occur in some animal products and aren’t considered harmful, and artificial, which are hydrogenated vegetable oils and have serious health consequences.

Artificial trans fats may increase your risk of heart disease.

In a series of clinical studies, people consuming trans fats instead of other fats or higher quality carbs experienced a significant increase in LDL (bad) cholesterol with a corresponding decrease in HDL (good) cholesterol (4).

Meanwhile, other naturally occurring dietary trans fats raise both LDL and HDL but they are not associated with increased risk of cardiovascular disease (4, 5).

Indeed, many observational studies link artificial or industrial trans fats to an increased risk of heart disease (4).


Both observational studies and clinical trials suggest that artificial or industrial trans fats significantly increase your risk of heart disease.

The relationship between trans fats and diabetes risk is not completely clear.

However, a recent study found no relationship between trans fat intake and diabetes (6).

Several controlled studies examining trans fats and diabetes risk factors, such as insulin resistance and blood sugar levels, show inconsistent results (7).

A 2021 animal study concluded that trans fatty acids significantly increased the risk of metabolic diseases such as type 2 diabetes and fatty liver (8).


Trans fats may drive insulin resistance and type 2 diabetes, but the results from human studies are mixed.

Excess inflammation is thought to be a primary cause of many chronic illnesses, such as heart disease, metabolic syndrome, diabetes, and arthritis.

Some studies indicate that artificial trans fats increase inflammatory markers when replacing other nutrients in the diet — but naturally occurring trans fats are not associated with inflammation (9, 10, 11).


Studies indicate that artificial trans fats increase inflammation, especially in people with excess weight or obesity.

Trans fats are believed to damage the inner lining of your blood vessels, known as the endothelium.

A small human study showed that a beverage with high levels of trans fat impaired the function of the lining of blood vessels and increased insulin resistance when compared with a high saturated fat beverage. This may help explain the association of trans fat intake with cardiovascular disease (12).

More recently, a study of 111 subjects with coronary artery disease found a clear correlation between increased consumption of trans fatty acids with the severity of their arterial lesions (13).

Recent studies have examined trans fats’ effect on cancer, finding a connection between trans fat intake and increase of breast, prostate, and colorectal cancers (14, 15).


Trans fats may damage the inner lining of your blood vessels and increase the risk of certain cancers.

Before the FDA restricted their sale, partially hydrogenated vegetable oils were the largest source of artificial trans fats in the diet because they were used to increase the shelf life of many foods such as crackers, cookies, snack cakes and other snack foods.

While they have been found in a variety of processed foods, governments have recently moved to restrict trans fats.

In 2018, the Food and Drug Administration (FDA) banned the use of partially hydrogenated oil in most processed foods in the US, effective 2020 (16).

Several other countries have taken similar steps to reduce the trans fat content of processed goods.


Processed food that contains partially hydrogenated vegetable oil is the richest source of trans fat in the modern diet. As of 2018, the use of trans fat in these products has been banned in the US.

Though trans fats have been banned in food in the US since 2020, it can be tricky to completely avoid traces of them.

In the United States, manufacturers can label their products “trans-fat-free” as long as there are fewer than 0.5 grams of these fats per serving.

Although manufacturers are no longer allowed to use trans fats as an ingredient, trans-fats are created in very small amounts when oils are processed with heat, also when you cook with oils at high heat. So despite the ban, it is possible to find small amounts in some foods.

Thus, it is wise to reduce the amount of highly processed foods in your diet.

Even so, because of the ban, we are mostly avoiding trans fats already without making much effort.


The FDA has banned trans fats in food since 2020. Trace amounts may still be found, but they are easy to avoid in food since the ban.

Most trans fats are hazardous to your health.

Although ruminant (natural) trans fats from animal products are considered safe in moderate amounts, artificial ones are strongly associated with health problems, including heart disease.

Artificial trans fats are likewise linked to long-term inflammation, insulin resistance, and even cancer, especially for people with obesity or excess weight.

Although the amount of trans fats in the modern diet has declined, the average intake is still a concern in many countries.