Two type of trans fat, trans fatty acids
In the previous article, we already discussed the differences between trans fats and cis fats. Trans fats contain one or more trans double bonds. Their structure and properties are more similar to saturated fats. Depending on whether they are biosynthesized, they are classified into natural trans fats (ruminant trans fats), and artificial trans fats (industrial trans fats). The trans fatty acids in natural fats are called rTFAs, and those in artificial fats are called iTFAs. Both types of trans fats are present in the daily diet where ruminant trans fats account for minority and majority is industrial trans fats.
Industrial trans fats primarily come from industrial production. When the double bonds are destroyed by high temperatures or catalysts, they will reform again, if there’re not enough hydrogen atoms. However, this time they tend to become the trans configuration because of their lower free energy. The partial hydrogenation and heating of edible oils (frying, refining and baking) are all the reasons for artificial trans fatty acids. Meanwhile, natural trans fatty acids come from microbial fermentation of linoleic acid in ruminant animal guts.
They aren’t a pure substance but a mixture of various fats. Whichever trans fats they are, fatty acids with 18 carbon atoms are dominant. 80-90% trans fatty acids are monoenoic acids that have only one double bond, and the rest are trans fatty acids that contain two double bonds. The double bond location is different on monoenoic acid. It’s on the ninth carbon in industrial trans fatty acids, while in natural trans fatty acids, double bond is on the eleventh carbon.
Hazards of Artificial or Industrial Trans Fats
Although trans fatty acids have been labeled as heart killers for a long time, recent studies show that these two types have different health effects distinctly. Natural trans fats not only don’t harm health but improve physical functions. In contrast, industrial trans fats harm health in multiple aspects.
High cholesterol, Inflammation, and Heart Disease
Artificial or industrial trans fatty acids increase the total cholesterol , triglyceride and LDL-C levels in blood. HDL-C or the good cholesterol also decreases. Research indicates that iTFAs are positively correlated with elevated levels of inflammatory markers, even exceeding those induced by saturated fatty acids. When volunteers consume iTFAs for a period, the inflammatory markers increase significantly, such as C-reactive protein, tumor necrosis factor and interleukins. This demonstrates industrial trans fats in everyday diet is relative to chronic inflammation that leads to a range of health risks such as cardiovascular disease, cancer diabetes, liver disease and atherosclerosis. American scientists had conducted a 14-year follow-up survey on 80,000 women aged 34 to 59. When iTFAs accounted for 2% of daily calories, heart disease incidence increased by 93%.
Fat Metabolism, Obesity, and Diabetes
Enzymes prefer to bind with cis fatty acids and rTFAs rather than iTFAs, leading to slower metabolism of iTFAs in human body. Long-term intake of iTFAs results in their accumulation on blood vessels walls. Artificial or industrial trans fatty acids also disrupt cell metabolism. Experiments in vitro have shown that cells absorb elaidic acid from culture dishes and integrate it into cell membranes. Since trans fatty acids are packed more tightly than phospholipids, the membranes viscosity increases and permeability reduces. Some nutrients and signa molecules may not penetrate the cell membrane.
iTFAs are often associated with obesity. The intake of artificial trans fatty acids will increase body weight, particularly as accumulation of abdominal fat. The American diet is high in artificial trans fats, so super-fat people with large waistlines are common on the United States streets. However, this’s rarely seen in Europe where rTFAs are primarily trans fats in diets.
Artificial trans fatty acids render cells insensitive to insulin and more insulin is produced for compensation. The pancreas overburdening increases the risk of diabetes. Although iTFAs don’t impact healthy and young individuals significantly, they exacerbate conditions for those who are obese or diabetic. In a 14-year survey of more than 84,000 U.S. women, 2,000 were diagnosed with type II diabetes. Researchers found that a 2% increase in dietary iTFAs raised the risk of diabetes by 39%.
Cognitive Impairments
Artificial trans fatty acids are also linked to cognitive impairments and Alzheimer's disease. Research from the 1990s found that people who had poor dietary habits in their teenage years had a higher incidence of dementia in old age. Older individuals who consumed more iTFAs experienced faster cognitive decline and smaller brain volumes.
Artificial trans fatty acids affect brain function in several ways. In brain, iTFAs increase β-amyloid protein whose nerve cell toxicity is a causes of Alzheimer's disease. The blood vessels that supply oxygen and nutrients to brain are blocked by elevated blood lipids. They cause mitochondrial oxidative damage and endoplasmic reticulum stress in brain neurons, ultimately activating cell apoptosis pathway. Furthermore, artificial trans fatty acids inhibit Δ-6 and Δ-9 desaturase to block linoleic acid to become polyunsaturated fatty acids.
Natural Trans Fats without Health Risks
The majority of trans fats in ruminant animals are conjugated linoleic acids (CLA) and vaccenic acid. It’s generally believed that natural trans fats don’t pose health risks. However, recent studies suggest that vaccenic acid still increase inflammation and cellular damage, although these side effects are less severe than those caused by elaidic acid. The health benefits mainly come from CLAs that come not only from ruminant animals but also from vaccenic acid conversion in our body. The inflammatory factors are reduced due to alteration of metabolic pathways. The antioxidant properties from two double bonds allow them to counteract free radicals. CLAs also enhance metabolic rate to reduce fat accumulation and increase muscle. Animal experiments have shown that they significantly reduce tumors incidence and decrease tumor proliferation, demonstrating their notable anticancer effects.