Trans fat, also called trans-unsaturated fatty acids, or trans fatty acids, is a type of unsaturated fat that occurs in foods. Trace concentrations of trans fats occur naturally, but large amounts are found in some processed foods. Since consumption of trans fats is unhealthy, artificial trans fats are highly regulated or banned in many nations. However, they are still widely consumed in developing nations, resulting in hundreds of thousands of deaths each year. Serious interest has been given to determining their sources, to better avoid them. Occurrence Some trans fats arise naturally, and some are the result of human actions. Naturally-occurring trans fats Trans fats occur in meat and dairy products from ruminants. For example, butter contains about 3% trans fat. These trans fats arise from the action of bacteria in the rumen. In contrast to industrially produced trans fats, the bacterial produced versions exist only as a few isomers. Polyunsaturated fats are toxic to the rumen-based bacteria, which induces the latter to detoxify the fats by changing some cis-double bonds to trans. As industrial sources of trans fats are eliminated, increased attention focuses on ruminant derived trans fats.The fats derived from vaccenic acid are found in breast milk. The trans fatty acid vaccenic acid has health benefits. Small amounts occur in meat and milk fat. Hydrogenation Trans fat can be an unintentional byproduct of the industrial processing of oils. Unlike naturally derived trans fats, the trans fats that result from hydrogenation consist of many isomers. In food production, liquid cis-unsaturated fats such as vegetable oils are hydrogenated to produce more saturated fats, which have desirable properties. For example, the shelf life of fats correlates with the degree of saturation: polyunsaturated fats are prone to autoxidation whereas saturated fats, being virtually inert in air, have very long shelf lives. Hydrogenation is practiced on a large scale in the production of margarine. The technology has improved such that a 2021 review indicate that the problem has been solved in modern countries. For example, trans fats levels can be minimized by using interesterified fat. Thermal isomerization When heated (cooked), some unsaturated fats change from their normal cis geometry to trans. The rate of isomerization is accelerated by free radicals. History The German chemist Wilhelm Normann showed that liquid oils could be hydrogenated. He patented the process in 1902. During the years 1905–1910, Normann built a fat-hardening facility in the Herford company. At