Almost 20,000 women provided data for the study, which looks set to increase the pressure on the food industry to remove trans fatty acids from their products and reformulate.
Writing in the American Journal of Epidemiology , Veronique Chajes from the Centre National de la Recherche Scientifique (CNRS) reports that high blood levels of trans fatty acids, but not cis fatty acids, was associated with a significant increase in breast cancer risk.
"A high serum level of trans-monounsaturated fatty acids, presumably reflecting a high intake of industrially processed foods, is probably one factor contributing to increased risk of invasive breast cancer in women," wrote the researchers.
"At this stage, we can only recommend limiting the consumption of processed foods, the source of industrially produced trans-fatty acid," they added.
Though trace amounts of trans fats are found naturally, in dairy and meats, the vast majority are formed during the partial hydrogenation of vegetable oil (PHVO) that converts the oil into semi-solids for a variety of food applications.
Trans-fatty acids (TFAs) are attractive for the food industry due to their extended shelf life and flavour stability, and have displaced natural solid fats and liquid oils in many areas of food processing.
But scientific reports that trans fatty acids raise serum levels of LDL-cholesterol, reduce levels of HDL-cholesterol, can promote inflammation can cause endothelial dysfunction, and influence other risk factors for cardiovascular diseases (CVD), has led to a well-publicised bans in New York City restaurants, and other cities, like Boston and Chicago, considering similar measures.
Epic results The seven-year study followed 19,934 women who provided diet history using a questionnaire and also provided blood samples at the start of the study.
Chajes and co-workers documented 363 cases of breast cancer during the course of the study, and matched these cases to breast cancer-free controls according to age, menopausal status at baseline, date, and collection centre.
While levels of cis-monounsaturated fatty acids were not related to the risk of developing breast cancer risk, the researchers calculated that increasing blood levels of the trans-monounsaturated fatty acids elaidic acid and palmitoleic acid were associated with a 75 per cent increase in breast cancer risk.
Prostate cancer worries, too At the start of 2008, researchers from Harvard reported that increased intakes of trans-fatty acids may increase the risk of non-aggressive prostate tumours by about 100 per cent.
The Harvard researchers report in the January issue of Cancer Epidemiology Biomarkers & Prevention (Vol. 17, pp. 95-101) that the highest blood levels of trans oleic acid and linoleic acids (18:1n-9t and 18:2t) were associated with a 116 and 97 per cent increase in the risk of non-aggressive prostate tumours, respectively, compared to the lowest levels.
Alternatives to trans fats The food industry as a whole has expressed its commitment to removing trans fatty acids from its products, but such reformulation is not straightforward and presents challenges.
Paul Wassell and Niall Young from Danisco's Multiple Food Application Group reviewed the options available to formulators and stated that designing foods with trans-fat alternatives must be a "multidisciplinary' approach" ( International Journal of Food Science and Technology , Vol. 42, pp 503-517).
"Successful replacements of trans fatty acids is not easily achieved by simply removing the trans isomer, because of a host of beneficial functional characteristics that are readily attributable to trans fatty acids," wrote Wassell and Young, pointing out that the presence of the trans isomer influences melting behaviour, oxidative stability and textural properties.
Source: American Journal of Epidemiology Published online ahead of print, Advance Access, 4 April 2008, doi:10.1093/aje/kwn069 "Association between Serum trans-Monounsaturated Fatty Acids and Breast Cancer Risk in the E3N-EPIC Study" Authors: V. Chajes, A.C.M. Thiebaut, M. Rotival, E. Gauthier, V. Maillard, M.-C. Boutron-Ruault, V. Joulin, G.M. Lenoir, F. Clavel-Chapelon