Hardened fats are created by converting oils into solid fats. These can be stored better when hardened, melt at higher temperatures and are therefore easier to use in practice than the original oils. Vegetable fats in hardened form were considered to be a healthier alternative to naturally solid fats according to the motto "Margarine makes the heart healthy", then they were suspected of promoting diseases. How healthy are hardened fats?
Hardened fats - an overview
- definition: Hardened fats are originally liquid fats and oils from which the liquid is extracted. There are partially hardened and completely hardened fats.
- advantages: Hardened fats have the advantage over oils that they are spreadable and easier to process.
- Formation of trans fatty acids: Partially hardened fats form trans fatty acids (also called "trans fats"). These could have a negative impact on health.
- What foods are trans fats found in?: Trans fatty acids are found particularly in industrially produced baked goods such as croissants, in fast foods such as French fries and potato chips and in finished products such as dry soups.
- Hazards: Trans fats can increase the risk of heart and vascular diseases. With a balanced diet, however, the risk of increased intake is low.
What does fat hardening mean?
Fat hardening transforms fatty oils into spreadable pastes. The double bonds of the unsaturated fatty acids are saturated with hydrogen. Unsaturated fatty acid glycerol esters become saturated fatty acids and the oil solidifies.
Typical products with hardened fats are margarine, vegetable shortening, cookies, industrially produced baked goods, spreads and the breading in finished products. Outside the food industry, hardened fats play a major role in the production of soaps.
Trans fatty acids - trans fats
In nature, unsaturated fatty acids exist mainly in the cis arrangement. When hydrogenating, however, the double bond changes, and this creates trans fatty acids, which are often referred to briefly as "trans fats". In these, the hydrogen atoms sit on opposite sides of the carbon atoms.
Such trans fats do not have a positive effect on health, more precisely: A positive effect has not yet been found. However, negative effects on the metabolism after consuming these fatty acids have been clearly demonstrated. If people ingest massive amounts of trans fatty acids, the risk of disrupting their fat metabolism increases, primarily because the LDL cholesterol in the blood increases and the HDL cholesterol decreases. A high intake of trans fatty acids probably also increases the risk of coronary heart disease.
The main groups of trans fatty acids are trans-octadecenoic acid (C18: 1tr), geometrical isomers of linoleic acid (C18: 2tr) and trans-hexadecenoic acid (C16: 1tr; trans-palmitoleic acid).
Hydrogenation is used to change the stability of oils in order to make better use of the fats. This turns liquid oil into margarine that can be spread on bread. When the unsaturated fatty acids are hardened, fatty acids in which double bonds are still present now arise in cis and trans states. Only when the fats have hardened are they completely saturated. For example, double-unsaturated linoleic acid first produces cis-oleic acid, then trans-elaidic acid and finally saturated stearic acid.
Trans fats in food
In food, trans fatty acids also occur in ruminant fat, but especially in food that is made from vegetable oils with hydrogenated fats. The most common of these acids in partially hydrogenated vegetable fats is trans-elaidic acid.
Until recently, margarine was the main source of these trans fatty acids. But today margarines contain only very small amounts of it, since the oils are completely hardened. An exception are margarines that contain only one type of oil, for example sunflower margarine. Here the oil cannot be fully hardened to achieve a spreadable consistency.
Trans fats are not considered good for health, and therefore the official guideline is to reduce trans fatty acids in food. The content of these acids in food is now declining.
Today, trans fats are particularly found in deep-fried industrial products made from potatoes, confectionery and ready meals such as pizza. 15 percent of the supply of trans fatty acids today comes from pizza and fried potato products. The proportion of acids in the respective products is very different.
Trans fatty acids and health
If the food contains many trans fatty acids, the concentration of LDL cholesterol in the blood increases, while that of the HDL cholesterol decreases. Put simply, LDL cholesterol is known as "good", HDL as "bad" for health. In addition, densified LDL particles are likely to be formed. The level of lipoprotein (a) increases. Both the compressed LDL cholesterol particles and an increased lipoprotein level are considered to be a risk for cardiovascular diseases.
A meta-analysis by de Souza et al. 2015 showed that an increased supply of industrial trans fatty acids, such as occurs during the partial hardening of fats, increases both the risk of cardiovascular diseases and the death rate if these diseases break out.
Fat metabolism disorder?
In 2015, the German Nutrition Society (DGE) mentioned in its evidence-based guideline on fat intake that increased consumption of trans fatty acids increases the risk of dyslipoproteinemia. It is a collective term for a group of disorders of the fat metabolism. In the same guideline, the DGE also considered a causality between increased intake of trans fatty acids and being overweight possible.
It is believed that the triglycerides in trans fatty acids promote high blood pressure and allergies, but the EU Food Safety Authority sees no studies that support this assumption.
Diabetes, stroke, metabolic syndrome?
There are also speculations that increased trans fatty acid intake increases the risk of type 2 diabetes mellitus, as well as high blood pressure (hypertension), stroke and the metabolic syndrome. According to the DGE, however, the evidence is not sufficient to make statements about it. Firstly, there were too few studies, and secondly, these would lead to conflicting results. A possible link between increased intake of trans fatty acids and carcinomas has not been sufficiently researched.
Are hardened fats safe or unsafe?
In the USA, partially hardened fats no longer fall under “generally recognized as safe”, which means that these fats have to disappear from food recipes. The DGE advises to minimize the intake of trans fats, which is not a problem with a wholesome diet.
The Federal Institute for Risk Assessment (BfR) sees no problem with trans fats in Germany, but wrote in a statement in 2013: "The level of trans trans fatty acid intake in Germany is harmless to health."
Do trans fatty acids lead to depression?
A team of scientists led by Almudena Sánchez Villegas from the University of Las Palmas in Gran Canaria evaluated the eating habits of more than 12,000 academics for a study over a period of six years. The subjects who consumed the most trans fats showed an almost 50 percent higher risk of developing depression.
Who consumes a lot of trans fats?
There is an increased supply of trans fatty acids in partially hardened fats, especially when eating fried fast food, low-quality margarines and industrially produced baked goods. Larger amounts of trans fats contain potato chips, dry soups, French fries, hardened frying and shortening fats.
On the other hand, those who reduce finished products and make sure to eat and drink a lot of vegetables, fruits, whole grains, rice, pasta or potatoes, as well as low-fat milk and milk products, run no risk of absorbing too many trans fatty acids.
Most transfatty acids in Germany today are found in young people between the ages of 16 and 24. The main cause here are fast foods such as French fries and potato chips.
Hardened fats - labeling requirements
Transfatty acids do not have to be declared separately in Germany. Refined oils and fats are labeled with their botanical origin, for example sunflower or palm fat. There is also an obligation to declare "hardened" and "partially hardened". (Dr. Utz Anhalt)
Author and source information
This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.
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- Federation for Food Law and Food Science (BLL): Guidelines for the minimization of trans fatty acids in food, 2012 (access: 13.11.2019), BLL
- Federal Institute for Risk Assessment (BfR): The current trans fatty acid intake in Germany is harmless to health. BfR Opinion 028/2013 of 6 June 2013, Berlin, BfR
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