Obesity, inactivity, age, and genetic predisposition are recognised risk factors for type 2 diabetes and pre-diabetes. Obesity, or more precisely, “the obesity epidemic” is said to be the driver of an increase in the incidence of type 2 diabetes and pre-diabetes. Folk are left with the impression that obesity causes type 2 diabetes. This is not true.
A risk factor is not the same thing as a cause. My favourite example is illiteracy. Short stature is a risk factor for deficient reading and writing skills. However, shortness is not the cause of illiteracy. Most short people are children and the reason they don’t read and write as well as adults is that they are still being taught. The cause of illiteracy is insufficient teaching and learning, not insufficient height.
Doctors have know for thirty years that fatter non-diabetic adults have more Beta cells (the cells which produce insulin) than lean non-diabetic adults. Recent high quality research demonstrating this can be read here.
The cause of type 2 diabetes and pre-diabetes is a prolonged period (years) of excess Beta cell death. Beta cells are found in the pancreas and they are the only cells which produce insulin, a hormone required for glucose to enter cells where it is used for energy.
The trigger for excess Beta cell death, in most people who develop type 2 diabetes and pre-diabetes, is a phenomenon called insulin resistance. Insulin resistance is the name doctors give to the observation that in some people the amount of insulin required to move a set amount of glucose into cells increases over time. This requires Beta cells to work harder, and as some fail and die, more and more is required from those which remain.