There are some things “everyone knows” about type II diabetes. “More and more people are getting it because as a community we are getter fatter and less active”. “The best way to prevent diabetes is to lose weight, and exercise more”.
There is some truth in all this. Some truth. Yes, the number of cases of diabetes is increasing, and is predicted to increase more. But the drivers of this increase are the ageing and the browning of the population, not our increased average weight and reduced levels of physical activity. This is uncontroversial.
Yes, fat people are more likely to develop diabetes. But, and it is a big but, most overweight people will never develop type II diabetes. This is also uncontroversial. The evidence comes from autopsy studies, particularly one from the USA published in the Journal of Obesity in 2015. This found that 35.4% of dead obese people had type II diabetes compared to 17% of dead non-obese people. The lifetime risk of developing type 2 diabetes if you are obese is around 35%. To put this another way, about two out of three people who try to reduce weight in order to avoid developing diabetes are wasting their time. They were never going to get type II diabetes.
The people most at risk of developing type II diabetes are those who are prediabetic. This is diagnosed through a simple blood test, the same one used to diagnose diabetes. About 10% of people with prediabetes become diabetic each year, compared to fewer than 1% of obese folk. This 10% figure is also uncontroversial. It comes from a very large study called the Diabetes Prevention Program or DPP.
To understand why this is so, we need to understand diabetes. All types of diabetes are the result of an imbalance between supply and demand. In every case, the body’s demand for insulin, the hormone which is an essential part of one pathway for moving glucose from the blood stream into cells, exceeds the capacity of the Beta cells in the pancreas to supply insulin.
The result of this inadequate supply of insulin, loosely speaking, (there is more going on) is that glucose spends longer in the blood before it is moved into cells and the average blood glucose levels rise. Glucose in the blood damages the cells lining small blood vessels and it is this damage which we see as the complications of diabetes – heart attack, stroke, blindness, kidney failure, and amputation.
Type II diabetes is characterised by a reduction, over years, of the mass of Beta cells. The total mass of Beta cells in an adult is around one gram. These have to supply the insulin requirements of 60-100kg plus bodies. Young obese people have a greater mass of pancreatic Beta cells than young slim people. This is also uncontroversial, and is also the result of autopsy studies. This is a point worth emphasising. Beta cells respond to increasing demand (more fat storage cells) by increasing their size and number. This is entirely analogous to the effect of weight training on muscle mass.
So what is it that overwhelms Beta cells and causes them to die off? Something called insulin resistance develops. Insulin resistance refers to the observation that, for poorly understood reasons, it, relatively suddenly, takes more insulin to move the same amount of glucose into cells. This is what overwhelms the Beta cells in people susceptible to diabetes. Insulin resistance can be diagnosed by measuring the blood insulin level first thing in the morning (fasting insulin). This blood test is not government funded.
The progression to type II diabetes is not weight gain plus inactivity. The progression is insulin resistance, prediabetes, then type II diabetes.
Although it is true, at a population level, that weight loss and increased exercise will slow the development of type II diabetes, this is not useful information for an individual. The key test is the one for prediabetes, and if that is negative, the fasting insulin test for insulin resistance. If you are not insulin resistant, then decisions about diet, weight loss, and exercise need not be motivated by thoughts of diabetes prevention. If you have prediabetes and struggle with diet and exercise, then a cheap drug, actually a plant extract, called metformin will probably improve and may well reverse your prediabetes. Unfortunately, although metformin is funded for the management of type II diabetes, it is not funded for the management of prediabetes although a number of GPs do prescribe it for this purpose.