Trans fat (also called trans fatty acid) is a type of unsaturated fat that has been artificially hydrogenated: a process in which hydrogen is forced through liquid vegetable oil, rearranging some double bonds in the fatty acid chains into a trans configuration. This changes the physical properties of the oil, making it more solid and shelf-stable, which led to partially hydrogenated oils being widely used in processed foods, margarines, and commercial frying.
Artificial trans fats have the most unfavourable cardiovascular risk profile of any dietary fat. They simultaneously raise LDL cholesterol (‘bad’ cholesterol) and lower HDL cholesterol (‘good’ cholesterol), creating a double negative effect on cardiovascular risk. This combination accelerates atherosclerosis (plaque build-up in artery walls) and significantly increases the risk of coronary artery disease, heart attack, and sudden cardiac death.
The evidence against artificial trans fats led to widespread regulatory action. The UK and EU banned or tightly restricted partially hydrogenated oils in food production, and industrially produced trans fats have largely been eliminated from the food supply. Small amounts of naturally occurring trans fats are present in meat and dairy from ruminant animals (such as cows and sheep), but these appear to carry a different, less harmful risk profile than industrial trans fats.
For cardiac arrest survivors and those at elevated cardiovascular risk, minimising intake of processed and ultra-processed foods is the most practical step to avoid residual trans fat exposure. A Mediterranean-style dietary pattern emphasising vegetables, fruit, wholegrains, oily fish, and unsaturated fats provides the most robust cardiovascular protection.
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