DEFINITION
Trans fatty acids (TFA)
are defined as unsaturated fatty acids containing one or more isolated (i.e. non-conjugated) double bonds in trans configuration.
SOURCES
The two major dietary sources for
TFA include production via industrial hydrogenation of vegetable oils (partially hydrogenated vegetable oils,
PHVO) from polyunsaturated fatty acids containing cis double bonds and through bacterial hydrogenation in the rumen.
Compared to unhydrogenated oils,
PHVO containing industrial
TFA (ITFA) are semi-solid, have a higher oxidative stability and a longer shelf life. Globally,
PHVO are commonly used in processed food products such as margarines, deep-fried foods, bakery and instant products as well as in confectioneries.
Sources of naturally derived TFA (ruminant TFA, R-TFA) are milk, dairy products and meat.
PHVO in industrially processed foods can contain up to 50% TFA, mainly elaidic acid (trans-9-octadecenoic acid, t9-C18:1, t9) and t10-C18:1 (t10). In contrast, ruminant fats generally have low quantities of TFA (1–8%), with t11-C18:1 (vaccenic acid, t11) being the predominant trans C18:1 isomer.
Trans fatty acid isomers and the trans-9/trans-11 index in fat containing foods. 2011
elaidic acid
vaccenic acid
DAILY INTAKE
In Western Europe, including Scandinavia, the average daily intake of IP-TFA ( industrially produced TFA) has decreased during the recent decade due to societal pressure and a legislative ban, whereas the intake of RP-TFA has remained stable.
In spite of this decrease in many countries consumption >20 g of IP-TFA in a one-meal menu consisting of some popular foods is possible, even though the average intake of IP-TFA in these countries is low. Subgroups of the populations may therefore, on average, consume >5 g IP-TFA per day. This level of consumption is generally not possible for RP-TFA. A daily intake of 5 g TFA (primarily IP-TFA) is associated with a 29% increased risk of coronary heart disease.
Ruminant and industrially produced trans fatty acids: health aspects 2008
METABOLISM
The dietary trans fatty acids are, for the most part, readily absorbed and incorporated into tissue lipids . The deposition of trans fatty acids in tissues may be selective. Thus adipose tissue and liver generally contain higher levels than other tissues. Minimum deposition of trans I 8: 1 occurs in the brain.
The trans fatty acids are converted to CoA esters and as such act as substrates for
acyl transferases and some desaturases. In general the trans 18: 1 seems to be treated
similarly to saturated fatty acid in the acylation of cholesterol and lysophosphatidylcholine.
Metabolism of trans fatty acids with emphasis on the effects of trans, trans-octadecadienoate on lipid composition, essential fatty acid, and prostaglandins: an overview.
HEALTH RISKS
- CORONARY HEART DESEASE
Intake of trans fatty acids is associated with a higher risk of cardiovascular disease because it is associated with :
- ↑ serum low density lipoprotein (LDL) cholesterol and ↓high density lipoprotein (HDL) cholesterol
- Endothelial dysfunction by increasing levels of several markers of endothelial dysfunction, including soluble ICAM-1 (sICAM-1), soluble VCAM-1 and E-selectin.
- ↓ NO
- perturbation of essential fatty acid metabolism by inhibiting the conversion of linoleic acid to arachidonic acid and to other n-6 PUFA, which cause changes in the phospholipid fatty acid composition in the aorta
- activation of systemic inflammatory responses, including substantially increased levels of IL-6, TNF-a, TNF receptors and monocyte chemoattractant protein
- activation of the NADH oxidase system (caused by stimulation of vascular endothelial cells by inflammatory cytokines) which plays a crucial role in generating reactive oxygen species, which in turn causes NF-KB activation leading to enhanced gene transcription of adhesion molecules.
- peroxynitrite (ONOO2) (because the increased production of O2 reacts with NO)
Peroxynitrite can not only uncouple and cause dysfunction
of endothelial NO synthase, but also can effectively nitrate tyrosine, tryptophan, cysteine, or methionine-free amino acids or amino acid residues in proteins. Nitration of proteins usually results in functional impairment and is an indicator of oxidative stress.
Trans Fatty Acids Induce Vascular Inflammation and Reduce Vascular Nitric Oxide Production in Endothelial Cell 2011
Trans fatty acids, lipoproteins, and coronary risk.
trans-fatty acids induce vascular inflammation and sudden cardiac death 2009
- DIABETES
Trans fatty acid-induced alterations in diaphragm phospholipid fatty acid composition and intramyocellular triacylglycerol content were associated with decreased insulin-stimulated glucose transport in the diaphragm. These observations suggest that dietary trans fatty acids decrease diaphragm insulin sensitivity, possibly due to increased intramyocellular triacylglycerol accumulation and decreased long-chain PUFA in phospholipids.
In conclusion they are associated to type-2 diabetes.
In a study on rats, the consumption of hydrogenated fat, rich in TFAs, by the mothers during the lactation period caused cardiac insulin resistance in the adult progeny because of a significant decrease in the cardiac content of glucose transporter-4 (P < 0.05) and in the hepatic content of glycogen (P < 0.05).
Dietary trans fatty acids alter diaphragm phospholipid fatty acid composition, triacylglycerol content and glucose transport in rats. 2005
Trans fatty acids in maternal milk lead to cardiac insulin resistance in adult offspring. 2008
- OBESITY
TFAs enhanced intra-abdominal deposition of fat, even in the absence of caloric excess, and were associated with insulin resistance, with evidence that there is impaired
post-insulin receptor binding signal transduction.
Trans Fat Diet Induces Abdominal Obesity and Changes in Insulin Sensitivity in Monkeys long-term TFA consumption is an independent factor in weight gain. 2007
- LIVER DYSFUNCTION
It seems that a strong relationship exists between the consumption of TFA in the oxidized oils and lipid peroxidation, decreased hepatic antioxidant enzyme activities (superoxide dismutase, catalase and glutathione peroxidase) and non alcoholic fatty liver disease (NAFLD).
The intake of high fat diet with different trans fatty acid levels differentially induces oxidative stress and non alcoholic fatty liver disease (NAFLD) in rats 2011
- ALTERED METABOLISM OF ESSENTIAL FATTY ACIDS
Trans fatty acids are competitive inhibitors of Delta-6 desaturase required for the linoleic acid and alpha-linoleic acid pathways; in this way they impair the synthesis of PGs, thromboxane, and prostacydin.
Prostaglandin and Diet
Metabolism of trans fatty acids with emphasis on the effects of trans, trans-octadecadienoate on lipid composition, essential fatty acid, and prostaglandins: an overview.
- RETINA DYSFUNCTION
The retina is more susceptible than the brain and the liver to the incorporation of trans isomers of DHA in rats consuming trans isomers of alpha-linolenic acid.
After dietary intake, TFA are distributed in the body and are incorporated into nervous tissues including the retina. In fact, after feeding rats with trans isomers of α-linolenic acid for 21 months, a linear incorporation of trans DHA (that is formed in vivo from the dietary precursor trans α-linolenic acid) and a decrease in cis DHA was observed in the retina, whereas no major changes were observed in the brain (that is also rich in DHA). In parallel to the modifications in retinal cis and trans DHA levels, the retinal functionality evaluated by the electroretinogram showed defects in animals that consumed trans α-linolenic acid.
The retina is more susceptible than the brain and the
liver to the incorporation of trans isomers of DHA in
rats consuming trans isomers of alpha-linolenic acid 2006
- ALZHEIMER’S DISEASE
In a vitro study trans fatty acids compared to cis fatty acids increase amyloidogenic and decrease nonamyloidogenic processing of APP, resulting in an increased production of amyloid beta (Aβ) peptides, main components of senile plaques, which are a characteristic neuropathological hallmark for Alzheimer's disease (AD). Moreover, the oligomerization and aggregation of Aβ are increased by trans fatty acids
Trans fatty acids enhance amyloidogenic processing of the Alzheimer amyloid precursor protein (APP). 2011
- MODIFICATION OF SPATIAL MEMORY
In a study on rats TFAs were incorporated in small amounts in the hippocampus and spatial memory was modified in young rats fed with a diet rich in TFAs.
Effects of a normolipidic diet containing trans fatty acids during perinatal period on the growth, hippocampus fatty acid profile, and memory of young rats according to sex. 2011
- ALTERATION OF IMMUNE SYSTEM
Short-term dietary intake of C18:1 trans fatty lead to a significant decrease in mitogen-induced CD69 expression on CD8+ T cells as well as decrease phagocytic activity on neutrophils.
This finding differs from results describing proinflammatory effects associated with long-term exposure to TFAs.
Short-term dietary intake of C18:1 trans fatty acids decreases the function of cellular immunity in healthy young men. 2008
- FETUS AND NEONATAL DEVELOPMENT
Because trans fatty acids in the fetal circulation must originate from the maternal diet, the maternal exposure to trans fatty acids is inversely related to long-chain polyunsaturated fatty acid status in full-term infants at birth. Because long-chain polyunsaturated fatty acids are important for early postnatal visual and cognitive development, factors that reduce the availability of longchain polyunsaturated fatty acids at birth are of serious concern.
In premature infants trans fatty acids in blood plasma correlated inversely with birth weight in an observational study, indicating that trans fatty acids may impair early human growth.
Inverse association between trans isomeric and long-chain
polyunsaturated fatty acids in cord blood lipids of full-term infants 2001
Metabolic aspects of trans fatty acids.
