What Is Wrong With Trans Unsaturated Fats?

Not so long ago, trans unsaturated fats — which are often called trans fats for short — were some of the most common components of many of our food. Even now, they are still very common in many countries, despite the many attempts taken to eliminate them from our diet entirely. Recently, trans unsaturated fats have got plenty of negative publicity, and rightly so. This type of fat is, in fact, almost non-existing in natural foods, and the evidence of its negative effects on human health is growing and growing as time progresses. We know that elevated level of trans fats are particularly damaging for the cardiovascular system.

Since you may have heard more and more about how unhealthy trans fats are, you might be wondering how exactly trans unsaturated fats could be impacting your body. We'll be looking at everything we know so far about why trans unsaturated fats are unhealthy and what consuming them can do to your body.

What are the trans fats?

The term “trans fats” refers to the type of organic molecules from the class of unsaturated fatty acids. Fatty acids belong to the group of carboxylic acids which contain long linear chains. They are major components of all fats of both plant and animal origin. Unsaturated fatty acids contain one or more double bond inside this chain. Geometrically, double bond may have either trans or cis configuration. As the name suggests, trans unsaturated fatty acids will have at least one double bond which is in the trans configuration.

Fatty acids can have different length and can also contain several double bonds. Depending on the structure of the fatty acid, they play different roles in cellular biochemistry.

From the point of view of human biochemistry and toxicology, trans fatty acids are important primarily because they are not normally present in natural sources of food. Unfortunately, modern food, like fast food for instance, contains lots of modified components, and trans fat is one of them. Trans fat is present in small amounts in normal dairy and meats, but nowadays humans are exposed to the amounts of trans fats that are significantly exceeding this norm.

Why modern food contains lots of trans fats?

Trans fatty acids were introduced to the food industry with the invention of partial hydrogenation process in the beginning of 20^thcentury. The process helps to convert unsaturated fatty acids of plant origin to saturated fat.

The term “saturated” refers to the absence of double bonds in the molecule of fatty acid. Saturation is achieved by hydrogenation, addition of hydrogen molecule to the unsaturated double bond.

Unsaturated fats are prone to randicity, the decomposition of fats due to oxidation and action of microorganisms which leads to the bad odor and decrease the quality of fat-containing food. Hydrogenation provides additional chemical stability to the fats. This increases their shelf life and reduces the need in refrigeration.

Partial hydrogenation of fats leads to the formation of trans fats as undesirable side products

Hydrogenation changes the double bond of unsaturated fatty acids into single bong. Full hydrogenation of unsaturated fatty acids leads to saturated acids that have no isomers. However, the purpose of hydrogenation is to harden the fat (saturated fatty acids have higher melting point than their unsaturated analogues) and reduce the amount of double bonds there, not to achieve the full saturation of double bonds as such. As a result, full hydrogenation is almost never done. Instead, a process of partial hydrogenation is widely employed. The use of only partial hydrogenation leads to the problem of formation of undesirable fatty acids as side product. It deals with the mechanism of hydrogenation. In the course of catalytic hydrogenation the double bond should get two additional hydrogen atoms. They never get added simultaneously. Attachment of first hydrogen leads to the intermediate without double bond, but still without the second hydrogen. Due to the absence of double bond, this intermediate is conformationally flexible. The first step of reaction is reversible. This means that the intermediate may lose the hydrogen and return to the original unsaturated state.  However, this return step may lead to the production of both cis and trans isomers without any preferences. As a result of partial hydrogenation, some molecules of cis fatty acids get isomerized into trans fats.

Production of hydrogenated fats quickly grew in popularity in the first half of 20^th century. As a result, now lots of fats in our food contain these artificially modified fats with significantly higher content of trans fatty acids.

Trans Fats Are Linked To The Health Damage

For a very long time, trans fat was considered perfectly safe. Moreover, trans fats from the margarine were considered a healthier option than saturated fats of butter. However, starting from the 1960s the evidences against the trans fats started to gradually accumulate. 

There is a significant body of evidences linking trans fats with various health problems and conditions. The exact mechanisms underlying these problems are not always known and continue to be investigated. One of the major theories is that unlike cis fatty acids, trans fatty acids cannot be metabolized by human lipase (enzyme splitting the fatty acids). This leads to the excessive accumulation of the trans unsaturated fatty acids in the body. They can inhibit different biochemical processes associated with fat metabolism.

Trans fat is particularly damaging for the health of heart

Excessive consumption of trans fats is linked to coronary heart disease.  Coronary heart disease is caused by formation of cholesterol plaques on the walls of blood vessels, particularly in the heart muscle. The process is accelerated by the high level of cholesterol in blood. The effect of trans fats consumption on the level of cholesterol is very well documented. 

Excessive consumption of natural saturated fats is also linked to the higher risk of heart problems. But trans fats seem to be more dangerous to the cardiovascular system. The difference between these two types of fats comes from the mechanism of their influence on the level of cholesterol.

Negative effects of trans fats are connected with the level of cholesterol

Blood cholesterol is often subdivided into two classes: LDL (so-called bad cholesterol) and HDL (so-called good cholesterol). The abbreviations refer not to cholesterol itself (chemically it remains exactly the same in both cases) but to high-density and low-density lipoproteins, the carrier proteins transporting cholesterol within the body. Cholesterol is an essential component of cellular biochemistry, human body requires certain amounts of cholesterol. However, modern processed food contains larger than normal amounts cholesterol. HDL effectively transports cholesterol to the liver where it gets metabolized. LDL, on the other hand, binds cholesterol quite loosely. As a result, molecule of cholesterol can be lost during transportation. Cholesterol is not soluble in aqueous media. Once it dissociates from the carrier molecule, it tends to precipitate to the walls of blood vessels. Thus, high level of LDL promotes the formation of cholesterol plaques, while higher level of HDL supports normal process of cholesterol elimination. Both saturated fats and trans fats increase the level of LDL. But unlike saturated fats, trans fats also reduce the level of good cholesterol, HDL. As a result, trans fats have two negative effects on the overall cholesterol level, which leads to particularly bad effect on heart.

Trans fats are associated with a number of other health conditions, such as diabetes  and cancer. Alzheimer’s disease and major depressive disorders were also linked to the excessive consumption of trans fats. Exact connections between trans fats and these conditions are still being investigated by researcher.

Trans fat is a significant concerns for health authorities around the world

Overwhelming evidences pointing to the connections between trans fats consumption and a number of serious health conditions caused many governmental and regulatory authorities around the world to introduce partial or total bans on the trans fats in the food.  Total ban was introduced in several European countries such as Denmark and Switzerland. Mandatory food labeling for trans fats is also introduced by many countries including UK. World Health Organization recommends limiting the amount of trans fats in foods by no more than 1% of calories intake.