Watch the Trans Fatty Acids - They Can Do Harm!

Summarized by Robert W. Griffith, MD
June 18, 2004

Introduction

Trans fatty acids (TFAs) are in the news because the FDA has required manufacturers to list them in their food labels. They are fatty acids that are formed when vegetable oils are hydrogenated, or partially hydrogenated, during the manufacture of fast foods, bakery goods, packaged snacks, and margarine.

For some time now it's been recognized that high TFA intake predicts an increased risk of coronary artery disease and diabetes. TFA consumption lowers HDL-cholesterol (the 'good' cholesterol) and raises LDL-cholesterol and triglycerides. But the link between high TFA intake and coronary artery disease is stronger than would be expected from the lipid changes it produces. And the lipid changes alone don't explain the increased risk of diabetes. Perhaps an effect on chronic inflammation in the body could account for the discrepancy. A study from Boston just reported in the American Journal of Clinical Nutrition, which is summarized here, provides some evidence of this effect.

What was done

Information was obtained from the Nurses' Health Study, which follows over 200,000 women aged 30 to 55 at baseline. About 60,000 of these women provided blood samples at intervals, and their diet was assessed by questionnaire every 4 years or so. A representative group of these women was selected; there were 823 subjects, aged 32 to 70.

To assess the presence of chronic systemic inflammation (systemic meaning 'throughout the body'), the following markers were measured in the blood samples: soluble tumor necrosis factor alpha receptors 1 and 2 (sTNF-R1, sTNF-R2), C-reactive protein (CRP), and interleukin 6 (IL-6).

Dietary intakes using food questionnaires were averaged for each subject, who were asked how often, on average, they had eaten given amounts of various specified foods during the previous year. From their answers, the TFA intake was calculated from tables of standard content of different brands of margarine, fats, oils, etc.

The women were assigned to one of five equally-sized groups (called quintiles), according to the amount of their TFA intake as a proportion of the total fat they consumed. Then analyses were done to look for possible associations between different levels of TFA intake and inflammation marker results. The analyses were repeated after making adjustments for other possible factors, such as smoking, pain-killer use, and alcohol consumption.

What was found

Overall, the average TFA intake was 4.7% of dietary fat; most TFAs came from food eaten away from home: cookies, donuts, sweet rolls, margarine, and crackers.

Increases in sTNF-R1 and sTNF-R2 were significantly linked to TFA intake - that is to say, the levels of these inflammation markers were higher in the higher quintiles, or fifths, of TFA intake, compared with those in the lowest TFA intake quintile.

There were no such linkages in CRP and IL-6 in the whole group of women. However, in women with increased body mass index (BMI) there was such a relationship. For every unit increase in average BMI, significantly higher CRP and IL-6 levels were found. (The researchers don't say from which BMI level upwards this effect was seen.)

These effects were independent of age, smoking, physical activity, medication use, alcohol consumption, and other dietary factors. And the sTNF-R1 and sTNF-R2 effects were not affected by BMI levels, unlike the CRP and IL-6.

What this means

Here's another example of how research is 'closing the loop' in finding out just how certain chronic diseases are caused. This time, the role of systemic inflammation has been clearly placed in the center of the connections between TFA intake and both coronary artery disease and diabetes. The increases in inflammation markers were independent of other factors, including lipid changes.

The 'take-home message' from this study is clear: keep your TFA intake as low as reasonably possible. You can do this by reading the labels carefully, and looking for 'no-trans' or 'low-trans' substitutes.

Source

• Dietary intake of trans fatty acids and systemic inflammation in women. D. Mozaffarian, T. Pischon, SE. Hankinson,  et al., Am J Clin Nutr, 2004, vol. 79, pp. 606--612

Related Links
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