“Kummerspeck” is one of those German words that is quite difficult or even impossible to translate. According to the Deutsche Welle, it refers to the extra weight you might put on after a bout of emotional eating.
So one might say something like, “My sister has been worrying a great deal about her new job. This has caused her to eat more than she normally does, which has lead her to put on a lot of weight.”
Now that’s quite a mouthful, isn’t it?