I was reading "Szlachetne Zdrowie" (No 7/2019) which is a Polish health magazine released by "Nasz Dziennik", which is a Catholic, very conservative newspaper of questionable quality. I read the chapter about microwaving written by Barbara Zielonka. She is a food technologist and claims that:
Microwaves frequency cause changes in organic compounds structure (isomers of those compounds might be created) and disintegration of many of them, with new, unknown chemical compounds unknown to nature being created. Food heated in microwave contains particles that are not created during conventional heating of the food (conduction, convection, radiation), where heat is transmitted from outside to the inside of the product.
(my own loose translation from Polish to English)
Also she claims that in The Lancet, there was some research showing that when the milk was microwaved, the amino acid proline in the milk changed its form from L-proline to D-proline and created so called "cis isomers". D-proline might be toxic, she claims. She also claims that the article in The Lancet is stating that "conversion of trans forms to cis forms might be dangerous, because cis amino acids are embedding themselves into peptides and proteins instead of trans isomers".
I was unable to locate that article in The Lancet.
So the bottom line is: is it true that microwaving food can create some kind of chemical compounds that are not created when heating the food in traditional ways? If yes, then should we be worried? Could any be dangerous, such as the mentioned D-proline? I thought that microwaving is safe because it is just making water molecules vibrate and thus warming up the food. On the other hand I am very sceptical of the mentioned source where I found this article, but it mentioned The Lancet and it got me interested.