You can read a simplified explanation here
http://en.wikipedia.org/wiki/Polyol_pathway
Basis of the issue (paraphrashed)
- The cells of the retinas,kidneys and nervous tissues are insulin-independent.
- The cells will use glucose for energy as normal, and any glucose not used for energy will enter the polyol pathway.
- In a hyperglycemic state, the affinity of aldose reductase for glucose rises (at normal levels the affinity is very low)
- causing an accumulation of sorbitol in the cells
- This sorbitol cannot pass through the cell membrane
- This sorbitol is processed further to fructose and removed from the cells (the next stage of the polyol pathway)
- This fructose is then processed in the liver affecting trig and VLDL levels.
This is one of the processes that it is thought that nerves, kidneys and eyes are damaged by high blood glucose levels. Remember the uptake by these cells is unregulated by insulin and once it has produced fructose that fructose is also unregulated by the action of insulin and also "turns off" your leptin receptors so you have a desire to eat more. It is all a nasty viscous circle. Low carb helps to short circuit this by keeping BG levels at normal levels (or there abouts).
That is why you generate more fructose as a diabetic than as a norm. You sit in an increased blood glucose level for much longer than a norm.
Well I hope that makes sense when you read it