> In a fire, we see firefighters, that doesn't mean firefighters cause fire. In diabetic patients, we see high glucose level. That doesn't mean eating high GI food causes someone to have diabetes.

This is correct but probably not in the way you think. It is not the glucose in and of itself that is the problem but the level of the hormone insulin circulating around your system that is at the root of Type II diabetes. Glucose and insulin are highly related. Insulin is released by the pancreas to help control the level glucose in our blood.

Virtually no insulin is required when metabolising fats, a small amount is required for protein and a larger amount of insulin is required when dealing with glucose dense carbohydrate based foods. The faster a carbohydrate is metabolised the greater the dose of insulin required to quell the resulting glucose rush in the blood.

What does the insulin do? As a hormone it has many functions. The presence of insulin in the blood signals to all cells to burn sugar (glucose) rather than fats (ketones) for their energy. It prompts the cells in the skeletal muscles to store up glucose in the form of glycogen for later use and it signals the liver to store excess glucose that is not immediately needed. Once the liver and muscles are full then the liver then converts any excess to triglycerides.

Where do the triglycerides go? They get stored as subcutaneous fat all over but largely in the belly (in men) and bum/upper legs (in women). What happens when subcutaneous stores are full? Then the triglycerides are shoved anywhere and everywhere. Fat is pushed into muscle cells as well as the cells in individual organs. The fat molecules present in cells in organs are particularly pernicious (visceral fat) but any cells that contain these triglycerides seems to disrupt the insulin signalling within the cell. This results in insulin resistance i.e., the ineffectiveness of insulin to signal to the cell to take up excess glucose.

When sufficient threshold of insulin resistance is reached, you will get higher blood sugar readings and a higher A1C at which point your doc will say you have prediabetes or full on type II diabetes.

Insulin is the master key variable that unlocks the type II diabetes puzzle. High blood sugar levels are just a symptom. The problem with modern day Type II diabetic care is they consider the high blood sugar as the root problem. So this is treated with meds such as metformin and eventually MORE insulin. Understanding type II diabetes as a disease of too much insulin sheds the disease in a very different light.

Anyway, you are correct, the high glucose level per se is not the cause, but high levels of insulin constantly circulating around your system is the big problem. Of course an effective way of doing that is to continuously eat foods dense in glucose and fructose that are metabolised very quickly e.g., cookies, ice-cream, orange juice etc.

> If we look at the Blue Zone, many people eat mostly carb. So carb/high GI food definitely doesn't cause diabetes

Blue Zone areas such as Okinawa, you do find people eating carb rich foods but they are also high in fibre e.g., root vegetables, sweet potatoes etc. look at books by Robert Lustig to learn more about the importance of fibre in relation to metabolism and diabetes risk.