On the one hand, there are naturally-occurring trans fats, which are derived from a bacterial transformation of unsaturated fatty acids in the first stomach of ruminants such as cattle. This is why trans fat is found in dairy products. Most animal fats are saturated fats (think tallow from beef and lard from pork, which are fats in solid form)
On the other hand are industrially produced trans fats, which are formed during manufacturing, primarily by partially hydrogenating oils. This is the process that allows vegetable oils to solidify. Unfortunately, the phenomenon of hydrogenating the oils used in frying simply occurs when the oil is repeatedly heated to a very high temperature. Under the effect of this heat, the cis fatty acid chains becomes trans.
Industrial saturated fats, meanwhile, have long been found in margarines. We used to completely hydrogenate natural unsaturated oils, which solidified them. But because the hydrogenation reaction was not perfectly complete, trans bonds were formed. For a long time now, margarine has therefore been a source of trans fat.
In the U.S., the food industry has until June 2018 to eliminate all sources of trans fat from their products. Canada will be banning trans fats in September 2018 . But whether it’s mandatory or simply because trans fats get such bad press, the industry will have no choice but to turn to vegetable oils – the so-called “non-trans fats”.
Vegetable oils are known as being monounsaturated or polyunsaturated; in other words, cis-form fatty acids. Because they do not raise bad cholesterol in the blood, these cis fats lower the risk of heart disease and are known as the “good” fats. They’re also known as Omega-3, -6 and -9.
The industry has already begun to use non-trans fats, but this shift has created its own new set of problems. Compared to the previously used partially hydrogenated oils (trans fats) or saturated fats, these monounsaturated and polyunsaturated oils are less stable and therefore more likely to rapidly degrade.