What? Zero Tolerance on Trans Fatty Acid Intake may be Irrational?
Game changer or media sensationalism? How can there be a headline that “not all trans fatty acids are bad for you”? Of course, one new study does not refute scientific consensus. However, important observations by Kleber and colleagues may change the course of nutrition guidance in the future.
Two types of trans fatty acids (TFA) are commonly found in the human diet. TFAs are ingested as meat and dairy products from ruminants and industrial fats, e.g. partially hydrogenated plant oils. Trans fatty acid intake has adverse effects on blood lipids and cardiovascular risk (CVD) although CVD risk may be affected by dietary source. It is recommended that TFA from partially hydrogenated vegetable oils be eliminated from the diet.
Denmark has banned the addition of industrially produced TFA to foods. When TFA intake is reduced, TFA concentrations in blood decline. In other words, we are what we eat. As is often the case in nutrition, a linear relationship does not exist between nutrient status and health outcome; this has even been reported for TFA.
It shouldn’t be surprising to learn low concentrations of total TFA in red blood cells (RBC) are inversely associated with adverse cardiac outcomes. Why? If populations at the low end of a U- or J-distribution are studied, the nutrient-risk relationship (including direction) can be VERY different than that observed in populations at the upper end of the nutrient status distribution. The LURIC study involved participants with a TFA index between 0.27% to 2.4% (% of total RBC fatty acids) whereas most Americans have a much higher TFA index range. The differences may be partially attributable to the fact that the European group is a relatively low contribution of TFA from partially hydrogenated plant oils.
Nutrients and foods are not good or bad. Too little can lead to deficiency diseases and metabolic perturbations. Excessive intakes may exert pharmacologic effects or even become toxic. Optimal health lies at the nadir of U- or J-shaped distributions of nutrient exposure. Evidence-based dietary recommendations require measurements of nutritional status.
In today’s main citation, the risk of consuming TFAs among patients with a history of CVD disease seems to depend upon the amount and regularity of TFA consumption (which drives RBC concentrations). It is likely the same for omega-3 fatty acids and many vitamins. Looking forward to more studies using biologically-based measures of nutrient exposure to study health outcomes.
Kleber ME, Delgado GE, Lorkowski S, Marz W, von Schacky C. Trans fatty acids and mortality in patients referred for coronary angiography: the Ludwigshafen Risk and Cardiovascular Health Study. 2015 Eur Heart J doi: 10.1093/eurheartj/ehv446
Laake I, Pedersen JI, Selmer R, Kirkhus B, Lindman AS, Tverdal A, Veierod MB. A prospective study of intake of trans-fatty acids from ruminant fat, partially hydrogenated vegetable oils, and marine oils and mortality from CVD. 2012 Br J Nutr doi: 10.1017/S0007114511005897
Astrup A. The trans fatty acid story in Denmark. 2006 Atheroscler Suppl doi: 10.1016/j.atherorsclerosissup.2006.05.010
Michas G, Micha R, Zampelas A. Dietary fats and cardiovascular disease: Putting together the pieces of a complicated puzzle. 2014 Atheroscler doi: 10.1016/j.atherosclerosis.2014.03.013
Schwenke DC, Foreyt JP, Miller ER, Reeves RS, Vitolins MZ, the Oxidative Stress Subgroup of the Look AHEAD Research Group. 2013 Am J Clin Nutr doi: 10.3945/ajcn.112.046508
Harris WS, Pottala JV, Vasan RS, Larson MG, Robins SJ. Changes in erythrocyte membrane trans and marine fatty acids between 1999 and 2006 in older Americans. 2012 J Nutr doi: 10.3945/jn.112.158295