Common sense dictates that fats found naturally in the diet that we’ve been eating for hundreds of thousands of years and have therefore evolved to eat and unlikely to be detrimental to health. For instance, saturated fat (a primal foodstuff if there ever was one) turns out not to have the heart-stopping properties we’ve been warned over for about for several decades. I wrote most recently about this here. Some naturally-occurring fats, such as omega-3 and monounsaturated fats appear to have health-giving properties.

One class of fats I recommend that people do avoid, however, is industrially-produced ‘trans fatty acids’. These are a by-product of what are known as ‘partially hydrogenated’ fats. These fats are unknown in nature, and have only made their way into our mouths since the processing of vegetable oils got underway in a big way very recently. The hydrogenation of fats allows vegetable oils (such as sunflower and safflower oil) to be solidified, which is obviously critical in the manufacturing of solid fats such as margarine. The other ‘benefit’ of hydrogenation is that it makes fats less liable to turn rancid (go off), which extends their shelf life.

The polyunsaturated fats that are the raw material for industrially produced partially hydrogenated and trans fats are ‘kinked’ and even coiled in shape. This physical form of fats is referred to as ‘cis’ (pronounced ‘siss’) configuration. However, in the processing of these fats not only adds hydrogen, but can also cause ‘cis’ fats to straighten out, forming what is known as the ‘trans’ configuration.

As expected, the research suggests that industrially-produced trans fats have the potential for wide-ranging unwanted effects on health. Trans fats have been linked with having adverse effects on heart health. For instance, in one study, individuals who had suffered a heart attack were found to have significantly higher levels of trans fats in their bodies compared to health individuals [1]. Those with the highest concentrations of trans fat were found to be, on average, more than 2½ times more likely to suffer from a heart attack than those with the lowest levels. A number of other studies also support the concept that trans fats are bad for the heart. Of four studies that have examined this potential association over time, three found that consuming just 2 per cent of our calories from trans fat is associated with an increased risk of heart disease of 28-93 per cent [2-4].

Trans fats seem to have the ability to impair the function of the hormone insulin, something that would be expected to increase the risk of developing type 2 diabetes [5,6]. Other research has found that, in women, a higher intake of trans fat is associated with an increased risk of diabetes [7].

All-in-all, the evidence suggests, as we would expect from primal theory, that industrially-produced trans fats are thoroughly unhealthy. In the UK, we consume an average of about 2.5-3.0 grams of trans fats per person each day [8]. This may not sound like much, except that studies show even very small amounts of these fats are associated with an increased risk of disease. In 2002, the Food and Nutrition Board of the Institute of Medicine in the USA published a report on the role of trans fats on health and made recommendations regarding safe levels of intake [9]. In the summary of this report, its authors suggest that the: “tolerable upper intake level of zero”. In normal language, this translates as “the safest amount of trans fats to consume is none at all.”

The adverse effects of trans fats, and the benefits of removing them from the diet was recently highlighted in an editorial published in the British Medical Journal [10]. In response to this article, a letter was published today in the BMJ that makes interesting reading I think [11]. It refers to the fact that the addition of trans fats to food (a widespread practice in food processing) is injurious to health. Here is the letter:

In many jurisdictions it is unlawful to render food injurious to health. For example, the UK Food Safety Act section 7 states: “Rendering food injurious to health: (1) Any person who renders any food injurious to health by means of any of the following operations, namely-(a) adding any article or substance to the food; (b) using any article or substance as an ingredient in the preparation of the food; . . . (2) In determining . . . whether any food is injurious to health, regard shall be had-(a) not only to the probable effect of that food on the health of a person consuming it; but (b) also to the probable cumulative effect of food of substantially the same composition on the health of a person consuming it in ordinary quantities.” Note the emphasis in section 7(2)(b) on probable cumulative effects when consumed in ordinary quantities. If it is the case that people on poor diets consume considerable amounts of industrial trans fatty acids, even where the average is quite low, it seems that using industrial trans fatty acids as food ingredients,1 in any foods that some consumers would eat regularly and frequently, may be unlawful in the United Kingdom.

The idea that the production of foods containing damaging trans fats is unlawful is an interesting concept I think. It does open up the possibility that legal action could be taken against food companies who manufacture these foods. Who might take such legal action? The Food Standards Agency? Don’t hold your breath: for some inconceivable reason the FSA has not even made it mandatory for food companies to declare the trans fats on product labels. However, a class action by some rightly disgruntled consumers is a distinct possibility and may have legs.

References:

1. Pedersen JI, et al. Adipose tissue fatty acids and risk of myocardial infarction – A case-control study. Eur J Clin Nutr 2000:54:618-625

2. Ascherio A, et al. Dietary fat and risk of coronary heart disease in men: Cohort follow up study in the United States. BMJ 1996:313:84-90

3. Hu FB, et al. Dietary fat intake and the risk of coronary heart disease in women. N EngI J Med 1997:337:1491-1499

4. Oomen CM, et al. Association between trans fatty acid intake and 10-year risk of coronary heart disease in the Zutphen Elderly Study: A prospective population-based study. Lancet 2001357:746751

5. Christiansen E, et al. Intake of a diet high in trans monounsaturated fatty acids or saturated fatty acids. Effects on postprandial insulinemia and glycemia in obese patients with NIDDM. Diabetes Care l997;20:88l-887

6. Alstrup KK, et al. Differential effects of cis and trans fatty acids on insulin release from isolated mouse islets. Metabolism I 999:48:22-29

7. Salmeron J, et al. Dietary fat intake and risk of type 2 diabetes in women. Am J Clin Nutr 2001;73:1019-1026

8. Hulshof KF. Intake of fatty acids in western Europe with emphasis on trans fatty acids: the TRANSFAIR Study. Eur J Clin Nutr 1999 53(2):143-57

9. Letter Report on Dietary Reference Intakes for Trans Fatty Acids Food and Nutrition Board, Institute of Medicine 10th July 2002

10. Mozaffarian D, et al. Removing industrial trans fat from foods. BMJ 2010; 340: c1826

11. Brock S N. Rendering food injurious to health. BMJ 340: c2981-c2981