Diabetes affects 8.3 percent of Americans of all ages, and 11.3 percent of adults aged 20 and older, according to the National Diabetes Fact Sheet for 2011. About 27 percent of those with diabetes—7 million Americans—do not know they have the disease. Prediabetes affects 35 percent of adults aged 20 and older.Wow-- this is a massive problem. The prevalence of diabetes has been increasing over time, due to more people developing the disorder, improvements in diabetes care leading to longer survival time, and changes in the way diabetes is diagnosed. Here's a graph I put together based on CDC data, showing the trend of diabetes prevalence (percent) from 1980 to 2008 in different age categories (2):
The diabetes epidemic has followed on the heels of the obesity epidemic with 10-20 years of lag time. Excess body fat is the number one risk factor for diabetes*. As far as I can tell, type 2 diabetes is caused by insulin resistance, which is probably due to energy intake exceeding energy needs (overnutrition), causing a state of cellular insulin resistance as a defense mechanism to protect against the damaging effects of too much glucose and fatty acids (3). In addition, type 2 diabetes requires a predisposition that prevents the pancreatic beta cells from keeping up with the greatly increased insulin needs of an insulin resistant person**. Both factors are required, and not all insulin resistant people will develop diabetes as some people's beta cells are able to compensate by hypersecreting insulin.
Why does energy intake exceed energy needs in modern America and in most affluent countries? Why has the typical person's calorie intake increased by 250 calories per day since 1970 (4)? I believe it's because the fat mass "setpoint" has been increased, typically but not always by industrial food. I've been developing some new thoughts on this lately, and potentially new solutions, which I'll reveal when they're ready.
* In other words, it's the best predictor of future diabetes risk.
** Most of the common gene variants (of known function) linked with type 2 diabetes are thought to impact beta cell function (<` href="http://www.ncbi.nlm.nih.gov/pubmed/19924209">5).