Trans Fatty Acids

Trans fats, unsaturated fatty acids with at least one double bond in the trans configuration, are formed during the partial hydrogenation of vegetable oils, a process that converts these oils into semisolid fats found in deep-fried foods, bakery products, packaged snack foods, margarines and crackers.  Partially hydrogenated oils (trans fats) are attractive to the food industry because of their long shelf life, stability during deep-frying, and their potential palatability in baked goods and sweets.

Consumption of trans fatty acids raises plasma lipid levels and increases the risk of coronary heart disease, sudden death from cardiac causes, and possibly diabetes.  The adverse health effects of trans fatty acids, still dangerously high in the US food supply, are far stronger on average than those of food contaminants or pesticide residues, which have received considerably more attention. 

The following are findings of a review conducted by Rubeen K. Israni, MD, Fellow, Renal-Electrolyte and Hypertension Division, University of Pennsylvania School of Medicine; April 13, 2006:

Lipid Levels: Consumption of trans fatty acids raises levels of low-density lipoproteins (LDL), reduces high-density lipoproteins (HDL) and increases the ratio of total cholesterol to HDL, a powerful predictor of coronary heart disease risk.  Trans fats also increase triglyceride levels, when compared with the intake of other fats.

Potential Molecular Mechanisms: Fatty acids are powerful modulators of cell function, altering membrane fluidity and responses to membrane receptors.  They appear to affect lipid metabolism, although these mechanisms are not well understood. 

Cardiovascular Disease:  On a per calorie basis, trans fats appear to increase coronary heart disease risk more than any other macronutrient, conferring a substantially increased risk at levels as low as 1% to 3% of total energy intake.  In a meta-analysis of four prospective cohort studies of nearly 140,000 participants, a 2% increase in trans fats was linked to a 23% increase in the incidence of coronary heart disease.  Also, levels of trans fats in erythrocyte membranes were associated with an increased risk of sudden cardiac death.  Further adjustment for levels of other membrane fatty acids found that high trans 18:2 levels (fatty acids with two double bonds in the trans position), were associated with a tripling of sudden death from cardiac causes.

Diabetes:  Here the findings are equivocal.  Two of the three studies cited found that trans fatty acids were not implicated in diabetes.  However, the third study of 84,941 female nurses followed for 16 years found a positive association, with a risk 39 percentage points greater in the highest quintile.   Molecular mechanisms that might account for a trans-fat effect in diabetes are not well understood, but evidence of trans-fat effects on metabolism in adipocytes and on systemic inflammation suggest plausible pathways. 


Given the adverse effects of trans fatty acids, the potential for harm is clear.  On the basis of the reported relationship between trans fat intake and coronary heart disease, 10-19% of coronary heart disease events in the U.S. could be averted by dramatically reducing intake of trans fats.  This translates into between 120,000 (10%) and 228,000 (19%) coronary heart disease events each year.


The FDA’s mandatory specifications for trans fat content on food labels required since January 2006 could be helpful but only if consumers READ THE LABELS.   They can be misleading.  For example, the law states that if a food contains less than .5 g (500 mg) of trans fatty acids per SERVING, trans fatty acid content may be listed as 0 on the packaging.  But we do not manage portion sizes, so we are likely consuming much more trans fatty acids than we realize.


Although the FDA acknowledges the potential harm from consumption of industrially produced trans fats, the agency nevertheless maintains that partially hydrogenated oils are basically safe.  A petition to the FDA called for removal of partially hydrogenated oils form the “generally regarded as safe” category.  Doing so would effectively eliminate the consumption of industrially produced trans fatty acids in the U.S.  Substantial reduction in these oils appears feasible and could be effected through legislation or voluntary efforts by food manufacturers. 


The researchers also asked that health care providers advise consumers about how to eliminate these risks by reading labels and making wise food choices, and they suggest that food manufacturers choose to use other fats in food production and preparation.


Primary Source: New England Journal of Medicine
Source reference: Dariush Mozaffarian, et al, “Trans Fatty Acids and Cardiovascular Disease,” New England Journal of Medicine 2006; 354: 1601-1613.