Natural vegetable oils present in nuts and seeds are healthy oils because they contain high concentrations of the essential fatty acids α-linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)). Alpha linolenic acid is desaturated and elongated in humans to form the long-chain fatty acids eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)), while linoleic acid can be elongated and desaturated for form dihomo-γ-linolenic acid (DGLA, C20:3 (n-6)). These long-chain more unsaturated fatty acids are important to the health because they form the series 1 eicosanoids (DGLA) and the series 3 eicosanoids (EPA and DHA) which have important cell regulatory functions regarding inflammation and disease. Evidence suggests that trans isomers of ALA and LA created during the hydrogenation of vegetable oil can interfere with this pathway by competitive substrate inhibition, resulting in reduced tissue concentrations of EPA, DHA and DGLA.
The ability of trans isomers of essential fatty acids to interfere with the accumulation of long-chain fatty acids in tissues has been demonstrated in rats during pregnancy and lactation. In the study1, pregnant rats were fed a diet containing either 10% soybean oil or 10% partially hydrogenated soybean oil. Analysis of the oil showed the soybean oil to contain no elaidic acid (t-C18:1 (Δ9)), a trans isomer of oleic acid thought to be responsible for most of the deleterious effects of trans fats, because of its high concentrations in partially hydrogenated oils. In contrast, the hydrogenated soybean oil contained 25.3% elaidic acid. No elaidic acid was detected in the stomach, plasma or erythrocyte membranes of the pups born to the soybean oil fed rats, but was detected in the pups of the rats fed hydrogenated vegetable oil. Elaidic acid was also detected in the brain tissue of the pups born to those rats fed hydrogenated vegetable oils.
High intakes of fish oils during pregnancy may be beneficial to the brain development of mammals because fatty fish contain high concentrations of DHA. This DHA is thought to accumulate in the neural tissue of the growing foetus where it alters neuronal activity. Research suggests that consumption of high concentrations of elaidic acid may interfere with DHA accumulation and cause the formation of abnormal foetal myelin during critical periods of brain development. This is concerning because intakes of hydrogenated vegetable oils have risen in line with increasing intakes of refined and manufactured foods. Consumption of trans fatty acids during pregnancy in humans may therefore have long-term implication for the health of the offspring because they alter brain function and structure. Because there is no known low safe level of trans fats, foods containing them should be avoided, particularly during pregnancy.
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