Is it true that calories from food begin to be "absorbed" into the body even in the oral cavity and that such a method of losing weight as "chewed and spat out" will not work?

Calories from food in the mouth are partially absorbed. But the chew and spat method does not work for weight loss as it is a symptom of an eating disorder. Now you are overweight, but if you start losing weight using the "chew and spit" method, in addition, you can get more mental disorder. Perhaps, in your case, it will help to start changing food habits with a change in attitude towards food. Switching to PP without reducing the amount of food and diet. Then change the mode, then reduce the volume. Step by step.

Opinion of the layman:
In negligible quantities. For example, some medications, absorption in the oral cavity occurs quickly, but you are unlikely to keep a large amount of food in your mouth for a long time. Glucose is absorbed, for example. But that won't give you any major calorie gain at all. In addition, by chewing food, you trigger the secretion of gastric juice, "turn on" the idle digestion mechanism, strain the pancreas, not sure if teasing your body is a good way to lose weight. Although, only a good doctor will tell you for sure. A quick change in eating behavior, just like a quickly gone weight - a lot of stress for the psyche and the body as a whole, is fraught with kickbacks, an oppressed state of the psyche, there is a great risk of returning back to the usual way of life. In my opinion, this issue should be approached slowly, delving into all the little things, and in no case be in a hurry. Connect work with the body, with consciousness, an integrated approach to everything. Much more important is the inner state during the transition. If you are not an athlete (and an athlete would not ask the crowd for advice on the Internet) - then even more so, in the name of change, do not force the body, make sure that the new diet brings joy, gives enough energy, does not take away health, and what is most important - has become a part of everyday life, a way of life, having ceased to be a boring "item" on the to-do list for the day, or a "magic pill".