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ETH - Eidgenoessische Technische Hochschule Zuerich - Swiss Federal Institute of Technology Zurich
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Published: 08.02.2007, 06:00
Modified: 07.02.2007, 21:28
ETH study “Trans Swiss Pilot”
Too many unhealthy trans fatty acids

Warning: nut chocolate croissants can harm your health, and so can ice-cream. A current ETH Zurich study reveals that such foods may contain harmful trans fatty acids made from partially hydrogenated fats. This is why the scientists are calling for at least an obligation for manufacturers to declare these ingredients.

Peter Rüegg

Various ready-made meals or bakery products, especially flaky pastry, can contain large amounts of trans fatty acids, which are a danger to health. For example, a selection of flaky pastries studied at ETH Zurich contained on average almost 8.5 percent of trans fatty acids relative to the total proportion of fats. So the amount of such fats in a total weight of 100 grams was 1.8 grams. This means that nut chocolate croissants, cream slices and coffee-break pastries are the trans fat content front-runners in the “Trans Swiss Pilot” study carried out by ETH Zurich. Trans fat is also occasionally found in ice cream, where the maximum value was almost 2 grams. Biscuits and potato chips may too contain excessive trans fats. However, it’s not just good versus evil: the researchers also found a low trans fats content in foods from all product groups. These are the results of the trans fatty acids study carried out by Eva K. Richter and Karem Albash Shawish in the context of their diploma theses supervised by ETH Zurich scientists Paolo Colombani and Martin Scheeder of the Department of Agricultural and Food Sciences with support from the Swiss Federal Office of Public Health.

Trans fats content can vary greatly

The ETH Zurich researchers faulted about 30 percent, or almost one in every three of the 120 foods from Switzerland that they examined. These identified foods show an amount of trans fatty acids as a proportion of the total fat content that is higher than the Danish limit value of two percent. However, the trans fat percentage can vary considerably. If a baker makes nut chocolate croissants using flaky pastry containing butter instead of the problematic partially hardened vegetable oil, the pastry does not pose any danger to health with regard to trans fatty acids. This is because the body can break down and metabolise the trans fatty acids occurring in animal fats.

The problematic trans fats are formed during the incomplete hardening of vegetable oils and fats. Partially hardened fats have the advantage that they melt at a desired temperature and thus have a firmness that is ideal for certain food manufacturing processes. As comparison: oleic acid, the main fatty acid of olive oil, is liquid above 13C, whereas a fully hardened fatty acid does not liquefy until 70 degrees or more.

In foods only since 80 years ago

Industrially produced partially hardened fats did not enter the human diet until about 80 to 90 years ago. In the early 20th century, stearin for candles was manufactured on a large scale from cheap fish and marine mammal oils. The oil was fully hardened to give it a high melting point. However, as the demand for candles dwindled, the machinery was no longer needed. It was converted to a different use and subsequently yielded hardened and partially hardened fats for human consumption. In the US, cottonseed oil was initially used as the raw material. Colombani says “Vegetable oils were chosen because they were more economical and because there was probably a shortage of animal fats at that time.”

The trans fatty acids problem

(per) A wide variety of fatty acids occur in nature. They consist of a carboxylic acid group and a carbon chain, which as a rule is unbranched. In the mono-unsaturated fatty acids, two carbon atoms in the chain are joined by a double bond. This double bond, which is naturally occurring in the cis configuration, bends the carbon chain at 30. If unsaturated fatty acids are partially hardened in contact with nickel catalysts in the presence of heat, pressure and hydrogen, the double bonds can be converted into the trans configuration and the bend in the carbon chain is “ironed out”. However, the double bond is retained. The crucial aspect of trans fatty acids is that the double bond can shift to a different position within the carbon chain. This forms various trans fatty acid isomers that can have an adverse effect on fatty acid metabolism enzymes in the body. The situation is different for vaccenic acid, which is produced by microbes in the first stomach of ruminant animals. Although this fatty acid is present as the trans isomer, the body can convert it into a conjugated linoleic acid (CLA). The latter is considered to be harmless and may possibly even inhibit tumour growth. This is why the trans fatty acids in butter or beef are regarded as harmless, in contrast to industrial trans fatty acids.


Depending on the fat used, flaky pastries such as these nut chocolate croissants have a trans fatty acids content that is harmful to health. large

Trans fatty acids do not occur in nature in the amounts made possible in industrial fats. In addition, incomplete industrial hardening produces various forms of trans fats that occur in nature in tiny traces at most. Natural trans fats occur mainly in animal products from ruminants such as cows. However, the human body can support these trans fatty acids in its metabolism and process them. Not so with the artificially created trans fatty acids from vegetable oils. Among other things, these interfere with the metabolism of the other fatty acids and increase the risk of diseases.

Just harmful, otherwise useless

Industrially produced trans fats are of no use to humans. “We do not know of a single piece of evidence of a beneficial effect,” says Colombani. On the contrary. According to several studies, ingesting four to five grams of trans fats per day increases the risk of cardiovascular diseases by 25 percent compared to a diet containing carbohydrates with comparable energy value.

Among other things, trans fats lead to a change in the blood cholesterol by reducing good and increasing bad cholesterol. This is currently regarded as an important risk factor for cardiovascular diseases including fatal heart attacks. Paolo Colombani adds that there is also said to be evidence that trans fats impair the metabolism of sugar and promote the onset of diabetes.Trans fatty acids also have an adverse effect at other biochemical levels in the body. They inhibit the enzyme that would otherwise form an unsaturated fatty acid from stearic acid, a saturated fatty acid.

Trans fatty acids probably damage not only those who consume them directly. It is likely that trans fatty acids enter unborn children through expectant mothers, a transfer that is being linked to adverse consequences for the development of the foetus. Furthermore, several studies show that the distribution of the various forms of trans fat in breast milk is the same as that present in partial hardening. Therefore a breast-fed infant can also ingest trans fatty acids of industrial origin. “That is certainly not a good idea,” says the ETH Zurich researcher. An initial study also reports an increased risk of infertility among women.

The industry and legislators must act

Colombani would like the industry to continue to intensify efforts already made to reduce trans fats. Legislators could also introduce an obligation to declare or even a statutory limit value as additional precautions. Danish industry quickly adapted to the change after a limit value was introduced in Denmark. That almost certainly involved additional costs. However, Colombani says that “Today this Nordic country’s fat industry is producing at the same costs as before.” In 2004 Denmark passed a law banning the excessive use of trans fats in foods and introduced the two percent limit for trans fatty acids relative to total fat content. The US, Canada and a couple of South American countries have since introduced a obligation to declare.

Switzerland obviously needs more time for authorities and foodstuffs manufacturers to fully implement a solution to the trans fats problem. Meanwhile there has been no lack of warning. After the end of the Second World War, Alfred Fleisch, then president of the Swiss Federal War Nutrition Commission, expressed concern at the use of food additives and called on foodstuffs producers to manufacture only those products whose effects on human health were known. His appeal faded away unheeded. Not until the nineties did the media take up the subject of trans fats. The fact that trans fatty acids are harmful to health was reported by Swiss television for the first time in 1997. Now, 10 years on, progress on the topic is beginning again in this country.

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