|
TFAs are produced when vegetable oils are ‘hardened’, a process which adds hydrogen to double bonds within unsaturated fatty acids. During the hydrogenation process, some polyunsaturated fatty acids (PUFAs) will only be partially hydrogenated, resulting in the formation of TFAs. Such fatty acids can also be produced in nature during the fermentation process which occurs during digestion in ruminant animals, e.g. cows and sheep. Consequently, they are present in small amounts in beef, lamb and dairy products.
TFAs have been found to have detrimental effects on a number of risk factors for coronary heart disease (Mozaffarian et al. 2006) and have recently been the cause of some controversy in the US where some ‘fast foods’ contain high levels. This web feature explores the current situation in the EU with regards to TFAs in foods, how the food industry has addressed the health concerns associated with these products in the EU and the challenges that reformulation of manufactured foods represents to food composition database compilers.
The first successful hydrogenation of oils took place in 1875 to produce candles from marine and plant oils. The partial hydrogenation of vegetable oils for use in food was developed as a means to improve the stability of the oils, giving them a longer shelf life. Through the hydrogenation process, the melting point could be manipulated to give fats with particular properties and different characteristics. It enabled oils such as soy bean oil to be used (which was not previously possible due to sensitivity to oxidisation) and it helped to reduce costs. The patent for hydrogenation or ‘hardening’ was filed in the early 20th century and, by the 1950s, millions of tonnes of oil were being processed in this way (Korver and Katan, 2006).
Evidence about the health risks from TFAs began to strengthen in the 1990s when human intervention trials began to show that their effects on risk factors for heart disease were at least as detrimental, if not more so, as the effects of saturated fatty acids (SFAs), which to date had received most of the emphasis in public health terms. SFAs have been found to contribute a large proportion of energy intake in some European countries (Hulshof et al 1999).
The TRANSFAIR study
Owing to concern about intakes of TFAs in Europe, which were estimated in the early 1990s to be between 2-17g per day, the European Commission funded the TRANSFAIR (‘trans fatty acids and risk factors for cardiovascular disease’) study to measure TFA intake in the EU. Fourteen countries in Western Europe took part in the study and data on the TFA content of foods in these countries were collected from 1995 to 1996. There was shown to be variation in the countries studied, with the lowest average intakes of TFAs in Greece and Italy (0.5% of energy, about 1g/day) and the highest average intake in Iceland (2.1% of energy, about 4g/day). Overall it was concluded that the current intakes of TFAs in Western Europe were not a major concern. Nevertheless, it was recommended that consumers reduce their consumption of all cholesterol raising fatty acids, including TFAs (Hulshof et al 1999).
Data from the TRANSFAIR study will be available via the EuroFIR portal as one of a number of specialised data sets.
Recommendations on TFAs
In 1994 the UK Department of Health published the recommendation that TFA consumption should not increase beyond the then current estimated intake in the UK of 5g/day or 2% of energy, and that consideration should be given to ways of reducing the amounts to TFA present in the diet. By 2000/2001, UK intakes had fallen to an average of 1.2% of energy intake in adults (Food Standards Agency 2003). In 2002 the Health Council of the Netherlands recommended that TFA should be limited to 1% of people’s energy intake. For an average diet consuming 2000 Kcals per day, this would equate to about 2.2g TFA per day. In 2003, the Danish government took matters further by specifying that industrially produced TFAs should not make up more than 2% of the fat content of any food as sold. This legislation did not apply to naturally occurring TFA.
What changes have industry made to the fat composition of foods?
The challenge to Industry has been to decrease TFA levels without increasing levels of SFAs. This has posed a number of practical difficulties as the solid nature of TFAs and SFAs could not simply be replaced by monounsaturated fatty acids (MUFAs) or PUFAs as they are liquid at room temperature.
Some margarine and spread manufacturers developed new technologies for the processing of fats and oils that allowed the formulation of spreads with appropriate structural characteristics that are low in both TFA and SFA. These blended ‘tropical oils’ such as palm oil, and seed oils such as sunflower seed oil or rapeseed oil can be processed for use in spreads, as outlined below.
A combination of three processes allows the creation of oils with the required properties (see figure 2):
· Fractionation: where the solid fat molecules in a fat mixture are crystallised and separated from the liquid molecules. Palm oil is most commonly processed in this way.
· Interesterification: a chemical process, which involves rearranging the structure of the fat molecules to make the fat more solid. Fractionation followed by interesterification can produce TFA-free fat of a suitable consistency for spreads in some cases.
· Hydrogenation: liquid oils may by fully hydrogenated before being processed using the techniques above (TFAs are produced by partial hydrogenation, full hydrogenation keeps the TFA content below 1%).
Figure 2. Outline of the production of TFA-free fats for spreads, adapted from Upritchard et al., 2005. Tropical oils may not have to be hydrogenated before processing (solid arrows) whereas all three steps are necessary to achieve the desired consistency for liquid seed oils (dashed arrows). | 
