I wonder if an analysis of the calorie content of fecal matter would give us a better idea of metabolic efficiencies. Of the 2000 calories the average adult needs to consume in order to maintain their weight, how much are they actually absorbing vs. how much is lost due to inefficiencies within the digestive process? That might explain why some people are able to live on what another would starve to death on. They aren’t extracting more calories than what’s there, it’s that the average person is extracting fewer calories than what’s there.
>>They aren’t extracting more calories than what’s there, it’s that the average person is extracting fewer calories than what’s there.<<
That could be part of it. Flora in the gut is destroyed by antibiotics. Different flora digest different nutrients. Some people’s bodies may be telling them to eat more, to get the proper nutrients into the bloodstream and to cells. The calories are stored as fat.
Also, if one is NOT getting those nutrients into the cells, the hypothalamus may be saying, “You’re starving!” so metabolism slows. It has been a very short time in the history of man that we have had an abundance of food. We were constantly in a feed/starve mode. Some bodies metabolized well to store more in preparation for lean times and cold. Eastern Europeans and Eskimos are examples.