In the USA the Food and Drug Administration (FDA) has just announced that it intends to take action that would reduce the amount of Trans Fatty Acids (TFAs) in foods to a minimum (1). It has been estimated that this would prevent 7,000 deaths from heart disease and as many as 20,000 heart attacks every year.
This topic has a long and interesting history. Much of the early work was done by Mary Enig who was a graduate student at the University of Maryland. She was very concerned about the conclusion of the McGovern Committee on Dietary Goals in 1977 that saturated fat (SFA) was linked to the development of cancer. As a consequence it was recommended that animal fats should be partially replaced by polyunsaturated fats, which invariably were from vegetable sources. She collated epidemiological data from a number of countries which were not consistent with this recommendation. Examples include the following:
- In America, the consumption of SFA had been declining steadily since the turn of the century, yet the cancer rate was rising sharply
- Greece had the same level of dietary fat intake as Israel, but only one-fourth the breast cancer rate
- Spain had a slightly higher dietary fat intake than France or Italy, but only one-third the mortality rate from breast cancer
- Puerto Rico, with a high animal fat intake, had a very low rate of breast and colon cancer.
- In the Netherlands and Finland both have the same level of animal fat intake – about 100 grams per person per day. But the Netherlands has twice the rate of both breast and colon cancer. The difference was that people in the Netherlands consumed 53 grams of vegetable fat per person compared to 13 grams in Finland
- A study in Cali, Columbia found a fourfold excess risk for colon cancer in the higher economic classes, which used less animal fat than the lower economic classes
- A study on Seventh-Day Adventist physicians, who avoid meat found they had a significantly higher rate of colon cancer than non-Seventh Day Adventist physicians
Although one must be careful in the interpretation of epidemiological data it is evident from the above that there is no consistent relationship between the level of SFA in the diet and the disease patterns. If anything, the results seem to suggest that there is a stronger link between vegetable oil/ polyunsaturated fat consumption and cancer, than between SFA and cancer (2).
During the 1980s the work at Maryland continued despite very limited funding (Mary Enig and other graduate students worked for little or no pay). Finally, in October 1983, their results were published.
What Enig and her colleagues found was that:
- Many margarines contained about 31% TFAs but later surveys found some brands to contain as much as 45% TFAs
- Many vegetable shortenings which were used in cookies, chips and baked goods contained more than 35 % TFAs
- Many baked goods and processed foods contained considerably more TFAs than were listed on the label
In fact their estimates indicated that the average American consumed at least 12 grams of TFAs per day. Rather ironically those who conscientiously followed the official advice and avoided animal fats would have been consuming far more than 12 grams TFAs per day. This was a direct contradiction of the assertions of the margarine industry that the maximum intake for most Americas was no more than 8 grams per day (3).
The dangers of the TFAs are now well established. The research group at the University of Maryland found that TFAs not only alter enzymes that neutralize carcinogens, and increase enzymes that potentiate carcinogens, but also depress milk fat production in nursing mothers and decrease insulin binding. Research in Czechoslovakia has shown that TFAs cause abnormal sperm to be produced. Paediatric researchers in Germany have found that excess TFA consumption is associated with low birth-weight babies. TFAs interfere with the utilisation of omega-3 fatty acids which causes impaired prostaglandin production (4).
Unfortunately, few people took any notice of these findings and researchers did not really attempt to tease out the roles of different types of fat in the diet. However in the 1990s, Walter Willett at the Harvard School of Public Health was conducting the Nurses’ Health Study. This produced data which showed that those nurses with the higher rates of cancer had actually consumed more margarine and vegetable shortenings. By contrast, those with a diet high in butter, eggs, cheese and meat had a lower incidence of cancer (5).
Further analysis of these data showed that the intake of TFAs was directly related to the risk of coronary heart disease. It was also found that intakes of foods that are major sources of TFAs such as margarine, biscuits, cakes and white bread were each significantly associated with higher risks of heart disease which is consistent with the hypothesis that consumption of TFAs contribute to the development of the disease (6).
As a consequence of these findings, it was accepted that action needed to be taken to limit the amount of TFAs present in the diet. Steps were taken by manufacturers to re-formulate products to reduce the TFA content of specific foods.
Here in the UK, a report by the Scientific Advisory Committee on Nutrition (SACN) summarised what had been achieved by 2007 (7). In 1986/87 the average intake of TFAs in adults was 2.2% of food energy but this had declined to 1.2% by 2000/2001. Based on information from the industry there had been a further fall by 2007 taking it down to 1.0% at the most.
A recent report provided detailed information on current levels present in a range of common foods (8). The foods analysed included pizza, garlic bread, breakfast cereals, quiche, fat spreads, a range of fish and meat products (retail and takeaway), chips (retail and takeaway), savoury snacks, confectionery and ice cream. Biscuits, buns, cakes and pastries were not included as these were analysed in a separate project, reported elsewhere. The products were purchased between January and April 2010 and the analysis was completed by February 2012. The results provide conclusive evidence that there has been a marked reduction in the levels of artificial TFAs in the vast majority of foods. The highest levels were found in battered deep fried fish purchased at takeaway chip shops. Relatively high levels were also observed in dairy products but these would have originated from the dairy cows. There is no indication that this type of TFA is in anyway comparable to those produced by the hydrogenation process with respect to damaging effects on human health.
On the whole there has been good progress in recent years but it took a long time for the industries and governments to tackle the problem. However there is still some way to go and the momentum must be maintained in order to reduce the amounts consumed to the absolute minimum.
- D Mozaffaran (2004) American Journal of Clinical Medicine 79 (4) pp 606-612
- W C Willett et al (1993) Lancet 341 (8845) pp581-588