my 30 years plus and last 4 years stopping mess would be:
a) pre diabetes is at point where while bg operating point is starting to drift up, body still regulating and skeletal muscle cells
have not saturated yet causing massive IR. Simple diet and exercise will contain and pull things back.
b) full on is where muscle cells and fat cells have large glucose load in local stores and one cannot haul the bg operating point back on diet/carbs control and hearty exercise. In fact meds intervention is needed to over come excees glucose generation/liver leak to keep BG down at 140 under. Sometimes carbs serious diet hall back plus meds needed to get saturation hauled back off of muscle/fat cells to enable body to regulate and then gradually increase diet back up but maintaining energy balance. Some suggest setting carbs load to be 20 per cent under daily need to be safe.
My read is that liver, pancreas and skeletal muscle cells form the servo system that sets BG operating point when gut has no glucose out. The liver provides a low level constant stream of glucose larger than what is basic use of brain, breathing, heart and pancrease sits there issuing stream of small insulin pulses to have skeletal muscles and fat cells pick up the excess and pancrease ups or slows the pulses to maintain BG at 80 to 90. This accounts for the tight regulation.
As liver ages its low level stream gets larger and pancreas probably drops its pulses slightly causing the set point to slip upwards. In early stages, change is small so that carbs diet/exercise changes are sufficient to regulate back.
As one gets even older, liver starts leaking worse and more causing muscle cells and fat cells to store more excess glucose and saturate causing insulin resistance.
My cgms and the prior 30 tests a day clearly expose liver as stinker over releasing the glucose when it shouldn't
in larger amounts when one ages even more to extent where carbs/diet control and more heraty exercise are not sufficient to overcome the excess glucose by liver release.
Hence the reason to load metformin to cut liver back.