Health effects of trans fatty acids (TFAs) on human organisms can vary according to their type, structure, composition, and origin
Dietary fats, including TFAs, have been one of the central topics of discussion in scientific literature and have received more attention from health professionals and the public than any other nutrients in the food supply . TFAs are unsaturated fatty acids containing at least one double bond in its trans configuration . Trans fat is the final product of a chemical process called partial hydrogenation of cis-unsaturated fatty acids.
Overall, there are four main sources of TFAs in the human diet; industrially produced TFAs by partial hydrogenation of vegetable oils, TFAs produced during heat processes, TFAs occurring naturally in ruminant sources, as well as TFAs synthesized for utilization as dietary supplements . TFAs are classified according to the two main sources they come from, “industrial” and “natural”. Industrial or artificial TFAs are produced during manufacturing by partial hydrogenation of liquid vegetable or fish oils containing unsaturated fatty acids. On the other hand, nTFAs are produced in the rumen of ruminant animals like cows, sheep, and goats by bacterial transformation of unsaturated fatty acids derived from feed. A small amount of TFAs is also present in poultry and pork fat [4,5].
| Chemical structure of the major TFA in the green box are nTFA
2. Health Effects of TFAs
Different data were found in relation to iTFAs, where a positive correlation between iTFA consumption and obesity was found. In the EPIC-PANACEA (Physical Activity, Nutrition, Alcohol, Cessation of Smoking, Eating out of Home, and Obesity) study, the doubling of elaidic acid was associated with a decreased risk of weight loss . In the Spanish INMA (INfancia y Medio Ambiente) study similar results were found in 4- to 5-year-old children. Indeed, iTFA intake of >0.7 g/day was positively associated with being overweight, including obesity; differently, in the same study, no significant association for nTFAs was found . The same results were confirmed in the cross-sectional study of Honicky and colleagues on children and adolescents who underwent a procedure to treat congenital heart disease. In this study, the patients that exceeded the iTFA intake recommendation of 1% of energy had a 5-fold increase of central adiposity . Some recent explanations have related the iTFA consumption with the increased genetic susceptibility of the obesity-associated gene polymorphisms (rs1121980, rs1421085, and rs8050136) and BMI or weight changes, highlighting the important role that iTFAs can have on human metabolism .
2.2. Cardiovascular Disease (CVD)
There are numerous studies providing evidence that iTFAs increase the risk of coronary heart disease . It has been stated that TFA consumption perturbs the body’s ability to metabolize essential fatty acids (including omega-3 fatty acids) leading to changes in the phospholipid fatty acid composition in the aorta, thus increasing the CVD risk 
There is a positive relationship between TFA intake and the incidence of breast and large intestine cancer . Similarly, more recently, Ardisson Korat and colleagues  found a positive relationship between TFA levels in red blood cell membrane and the risk of large B cell lymphoma, especially for elaidic and vaccenic acid . Matta et al.  support the hypothesis that higher dietary intakes of iTFAs, in particular elaidic acid, are associated with elevated breast cancer risk.
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