I could not find any materials on extended fasting
While this has been studied, I believe that the studies have been pretty small. Fung presented some data in one of his lectures, though I forget which one.
Anyway, in the data he showed fasting did not seem to reduce BMR more than you would expect due to lose of body mass. I believe the same was true of ketogenic diets. The main culprit for reduced BMR seemed to be carbohydrase based diets. It seems like the issue is elevated insulin while at a caloric deficit preventing there body from using fat forcing the body to reduce caloric expenditure. That said, I have not seen where that was studied directly. I have only seen the logical connection made between experimental date showing reduced metabolism during low calorie high carbohydrate diets and the fact that insulin causes the body to store energy.
Well yes. You’re not expending energy digesting food, you’re likely going to feel tired so moving less, you’re going to lose weight so you’ll have less energy to move.
This is all normal.
When you’re obese your metabolic rate may be higher only because your body is maintains hundreds of extra pounds.