I just read that chewing and swallowing normally elicit a parasympathetic response, in and of themselves. The process of eating tells the body to calm down.
I had never encountered this factoid before. It explains a lot, even before one gets into the effect of fats and simple sugars on cortisol.
Put another way, if I might expand to a cultural comment, our bodies naturally want to enjoy meal times, and make them stress free and relaxed.