Once you get into sugar metabolism, and its regulation, you are in a complex web of science and opinion in which nearly a century of research has failed to give a cause, merely associations and risk factors. We do know proximate causes and mechanisms (this causes that type of stuff) but not enough to really understand what is going on.
Let me give you an example of the complexity: we know CFS is a high oxidative stress disorder. This attacks omega 3 fatty acids. We also know that we benefit from omega 3s, in both brain and immune function. How many people are aware that the omega 3 content of the nuclear membrane inside cells regulates, in part, the insulin response? That omega 6s do too, although in CFS we are often deficient both through poor synthesis of omega 6 substrates for its hormone derivatives, and probable hyperutilization to make inflammatory hormones?
There are also indications that the cleaved RnaseL fragments often found in CFS might have metabolic effects. Then we have all the cytokines, many of which are still under investigation. I have my opinions, based on more than 15 years of interest in this area, but I have to admit I don't understand it. Then, I also think that nobody else does either. This is very very very complex.
I would like to say that I think many cases of type 2 diabetes found in CFS are not caused by the standard problems, they follow different biochemical rules, show up differently in lab results, and are even more misunderstood than regular type 2 diables.
I am a type 2 diabetic. I have read hundreds of research articles on this (most of which are biased) but I do think one thing: the control systems (metabolic, hormone and neurological) that regulate this metabolism need a lot more research. My suspicion is that we need to follow the hormones, as well as the epigenetics (which genes are switched on or off), specifically for CFS and not generally.
This is one area in which I think we can only use the science as a rough guide, which is why I am always interested in reading about people's practical experience. Science does have its limitations, particularly in areas that attract no funding. The combined wisdom of the neuroimmune disorder community will probably be our best guide.