Trans fatty acids

There is a lot of disagreement when it comes to nutrition, but if there is one thing that virtually all experts agree on, it is the harmful effects of trans fats. Fortunately, the consumption of these unhealthy fats has decreased over the last few years, but we are still consuming far too much of them, which can have devastating effects on our health. This article will take a closer look at trans fats, what they are, why they are so bad for our health and how to avoid them.

What are trans fats?

The hydrogenation of edible oils is an industrial process that uses hydrogen (hydrogenation) to convert unsaturated fatty acids from vegetable oils into solid or semi-solid fats. This makes them easier to process, more spreadable and more durable. Hardening produces modified chemical structures from natural unsaturated fatty acids.

The (partial) hardening of vegetable oils

improves the color of an oil
turns liquid oils into spreadable and hard fats
changes unsaturated fatty acids into chemically modified fatty acids
makes oils less susceptible to free radicals and therefore more durable
worsens the fatty acid profile with increased intake

Once changed, trans fatty acids can no longer be converted back into the natural form of unsaturated fatty acids. In addition to trans fatty acids, the hardening of edible oils also produces other altered structures that have not yet been studied in terms of their possible harmful effects. The disadvantage of hardening is a worsened fatty acid profile with possible harmful effects on health if the intake of trans fatty acids is too high. Unlike saturated fats, which have no double bonds, unsaturated fats have at least one double bond in their chemical structure.

This double bond can have either a "cis" or a "trans" configuration, which refers to the arrangement of hydrogen atoms in the region around the double bond. Basically, "cis" means "same side", which is the most common structure. In trans fats, the hydrogen atoms are on opposite sides, which can be a problem. "trans" is the Latin term for "on the opposite side", from which the name trans fat is derived. This chemical structure is thought to be responsible for numerous health problems.

Figure 1: Saturated fatty acid without a double bond, as found in butter.

Figure 2: Unsaturated fatty acid with a "cis" double bond, as found in vegetable oils.

Figure 3: Unsaturated trans fatty acid with a "trans" double bond, as found in some types of margarine.

Summary: Trans fats are unsaturated fats that have a specific chemical structure in which the hydrogen atoms are on opposite sides of the double bond.

Natural vs. artificial trans fats

Natural trans fats have been part of the human diet since humans began eating the meat and milk of ruminants (cows, sheep and goats). This type of trans fat is produced when bacteria in the stomach of these animals digest grass. These trans fats account for up to 2 to 5% of the fat in dairy products and 3 to 9% of the fat in meat from these animals (1, 2). However, people who eat meat and dairy products do not need to worry about this. Several studies have concluded that a moderate intake of these natural trans fats does not appear to be harmful (3, 4, 5). The best known variant of these naturally occurring trans fats is conjugated linoleic acid (CLA), which may have potential health benefits and is often taken as a supplement (6, 7, 8, 9). This fatty acid is found in relatively large quantities in the milk fats of grass-fed cows, which are considered extremely healthy and may reduce the risk of heart disease (10, 11).

However, the same positive things cannot be said about artificial trans fats, also known as hydrogenated fats. These fats are made by pumping hydrogen molecules into vegetable oils. This alters the chemical structure of these oils and changes their form from liquid to solid (12). This process involves high pressure, hydrogen gas and a methyl catalyst and it seems highly disgusting...the fact that anyone would consider the end product suitable for human consumption is disturbing. Once the vegetable oils have been hydrogenated, they have a longer shelf life and are solid at room temperature - giving them a consistency similar to saturated fats. Even though humans have been consuming natural trans fats for a very long time, this is not the same as artificial trans fats, which pose a serious risk to health.

Summary: Natural trans fats are found in some animal products and are harmless. Artificial trans fats are produced by hydrogenating vegetable oil in a chemical process.

Trans fatty acids in margarines

The (partial) hardening of vegetable oils is an important element in the production of margarine. Their trans fatty acid content varies and depends on which and how much hydrogenated oils are used. The trans fatty acid content of spreadable fats ranges from 1 % to 17 %, while the proportion can be higher in hard margarine. However, the content of trans fatty acids in many types of margarine today is kept rather low, as the possible harmful effects of trans fatty acids are now known.

Potential health risks caused by trans fat

Trans fats can increase the risk of heart disease.

Over the last few decades, numerous clinical studies have been conducted on the subject of trans fats. In these clinical trials, people were given trans fats (in the form of hydrogenated vegetable oils) instead of other fats or carbohydrates. The health effects were studied by measuring known risk factors for heart disease such as cholesterol or lipoproteins that transport cholesterol in the body. Replacing carbohydrates (1% of calories) with trans fats increased levels of "bad" LDL cholesterol, but not levels of "good" HDL cholesterol. In contrast, most other fats tend to increase both HDL and LDL cholesterol levels (13).

Replacing other dietary fats with trans fats increased the ratio of total cholesterol to HDL cholesterol and had negative effects on other lipoproteins (the ApoB:ApoA1 ratio), both of which are important risk factors for heart disease (14). However, the results of these studies go far beyond risk factors. There are a number of observational studies that directly link trans fats to an increased risk of heart disease (15, 16, 17, 18).

Summary: Both observational and clinical studies have found that trans fats significantly increase the risk of heart disease.

The influence of trans fats on insulin sensitivity and type II diabetes

The relationship between trans fats and diabetes risk is not completely clear. A large-scale study of over 80,000 women found that the women who consumed the most trans fats had a 40% higher risk of diabetes (19). However, two other similar studies found no relationship between trans fat consumption and diabetes (20, 21). Several controlled human studies have looked at trans fats and important diabetes risk factors such as insulin resistance and blood glucose levels. Unfortunately, the results have been inconsistent. Some studies appear to show harmful effects of trans fats, while others show no effects (22, 23, 24, 25, 26).

However, several studies conducted in animals have shown that large amounts of trans fats have negative effects on insulin and glucose function (27, 28, 29, 30). Of particular note, a 6-year study in monkeys found that high trans fat intake (8% of calories) caused insulin resistance, abdominal obesity and increased fructosamine levels - a marker for high blood glucose (31).

Summary: It is possible that trans fats may cause insulin resistance and type II diabetes, but the results of human studies are mixed.

Trans fats and inflammation

Excessive inflammation is believed to be one of the leading causes of many chronic Western diseases. These diseases include heart disease, metabolic syndrome, diabetes, arthritis and numerous others. There have been three clinical studies that have examined the relationship between trans fats and inflammation. Two of these studies concluded that trans fats increase inflammatory markers such as IL-6 and TNF alpha when they replace other nutrients in the diet (32, 33). The third study replaced butter with margarine and found no difference (34). In observational studies, trans fats have been associated with increased inflammatory markers including C-reactive protein, particularly in people with high body fat (35, 36). Looking at these study results, it seems quite clear that trans fats are an important pro-inflammatory factor, which can potentially lead to all kinds of problems.

Summary: Clinical and observational studies suggest that trans fats cause inflammation, which is especially true for overweight and obese people.

Trans fats, blood vessels and cancer

Trans fats are believed to damage the inner lining of blood vessels, also known as the endothelium. When saturated fats were replaced with trans fats in a four-week study, HDL cholesterol levels dropped by 21% and the ability of blood vessels to dilate was reduced by 29% (37). Markers of endothelial dysfunction were also increased when trans fats replaced carbohydrates or monounsaturated fats (38). Unfortunately, very few studies have examined the relationship between trans fats and cancer. In the study known as the Nurses' Health Study, pre-menopausal trans fat consumption was associated with an increased risk of breast cancer after menopause (39). However, two review studies concluded that the link to cancer was very weak. So far, no convincing link has been established (40).

Summary: Trans fats can damage the inner lining of blood vessels, which can lead to a condition known as endothelial dysfunction. The effects on cancer risk are less clear.

Other health risks of trans fats

Trans fatty acids interfere with other bodily processes. For example, they can contribute to increased cell permeability. This makes it easier for harmful substances to enter the cells and disrupt their natural processes. Trans fatty acids can also weaken the immune system, for example by impairing the function of B lymphocytes.

Trans fats in the modern diet

Hydrogenated vegetable oils (the primary source of trans fats) are cheap and have a long shelf life. For these reasons, they are found in all kinds of modern processed foods. Fortunately, the consumption of trans fats has decreased in recent years due to awareness campaigns by health organizations. In 2003, the average American consumed 4.6 grams of artificial trans fats per day. This amount has since dropped to 1.3 grams per day (41, 42). In Europe, the Mediterranean countries are the countries with the lowest consumption of trans fats. This could at least partly explain the low risk of cardiovascular disease in these countries (43, 44). People who consciously avoid the intake of animal fats (e.g. vegans) generally consume more than 12 grams of trans fatty acids per day. However, even if the consumption of artificial trans fats is lower today than in the past, it is still too high and should ideally be zero.

Summary: Consumption of trans fats has fallen significantly in recent years, but is still high enough to cause harm.

People who should avoid trans fats as much as possible

Pregnant women
Infants and children
Overweight people
People with an increased risk of (non-insulin-dependent) diabetes mellitus or disease
People with an increased risk of cardiovascular disease or illness
People with an increased risk of cancer or disease
Athletes, bodybuilders, athletes in general.

How to avoid trans fats

Although there has been great progress in recent years, trans fats are still present in many processed foods. In some countries, food manufacturers are allowed to label their products as "trans fat free" if they contain less than 0.5 grams of trans fat per serving. A few "trans fat-free" cookies can quickly add up to harmful amounts of unhealthy trans fats. To make sure you're actually avoiding trans fats, look carefully at the list of food ingredients and avoid products that list "hydrogenated" or "partially hydrogenated" fat on the ingredient list.

Unfortunately, checking the label is not enough in all cases. Some foods (such as ordinary vegetable oils) may contain trans fats without them appearing on the label. An American study that checked soybean and canola oil samples from the supermarket found that between 0.56 and 4.2% of the fats consisted of trans fats without this being stated on the label (45). The best thing you can do to avoid trans fats is to avoid processed foods completely. Choose real butter instead of margarine and olive oil or coconut oil instead of potentially harmful vegetable oils...and take the time to cook your own meals instead of resorting to fast food.

Conclusion

Natural trans fats from animal products are safe, but industrially produced, artificial trans fats are toxic. Studies have found strong links between these fats and cardiovascular problems, including heart disease. Consumption of trans fats has also been linked to long-term inflammation, insulin resistance and an increased risk of type II diabetes, especially in overweight people. Even though the amount of trans fats in the modern diet has decreased, the average intake is still dangerously high. Unfortunately, the claims on labels of processed vegetable oils and junk food cannot always be trusted. Many supposedly trans fat-free products still contain trans fats.