Insulin resistance, the hallmark of prediabetes, is compensated for by an increase in insulin output. Since the pancreas will eventually work itself to death it would behoove us to decrease the work load of this poor organ. A great deal of work has gone into understanding the factors that regulate insulin resistance and as it turns out; simply exercising regularly is sufficient to maintain a degree of insulin sensitivity. We understand many aspects of how exercise does this down to the molecular details and sometime I will describe those details. Today, however, I am more interested in considering the effect of exercise on the beta cells – the producers of insulin.
A group of Duke University researchers led by Dr. Chris Slentz has addressed this issue and the results are published in the most recent issue of Diabetes Care. This work is part of a much larger study involving exercise and diabetes (the STRRIDE project). The authors chose sedentary people with type 2 diabetes who were between 40 and 65 years of age. They had to be able to exercise and could only be mildly overweight (not obese). Risk of heart disease was also a reason for exclusion from the study. Both men and women took part.
The authors randomly assigned the subjects to one of three exercise groups or a control group (that presumably watched TV). The three types of exercise were (1) high intensity and lots of it, (2) high intensity but only for a short period of time and (3) moderate intensity and for that same short period of time as group 2. The exercise was done on either treadmills or elliptical trainers and was monitored by research staff so I would assume that no cheating occurred.
Insulin action was determined after exercise using a complicated but very powerful procedure. Glucose was administered by catheter and blood samples taken for a time. Then insulin was administered directly into the blood through the same catheter and additional blood samples were taken. This allowed the researchers to monitor both the degree to which the subject’s pancreas was responding to blood sugar levels as well as the ability of insulin receptors to mobilize glucose transporters to remove glucose from the blood.
Of the 387 people who entered the study, 260 completed it. Of these 237 had complete glucose tolerance data and these were used to generate the data presented. All three exercise groups showed improvement in insulin sensitivity which was not a surprise. Basically, any exercise (including taking the stairs or walking from a far away parking space) will help insulin resistance. More exercise generally leads to better results. Also, as expected, the exercise groups showed decreased visceral fat and triglycerides. They also lost a little weight but not enough to matter. The surprise came when the researchers looked at beta cell function. They found that while all 3 groups showed some improvement, the low intensity low duration group did far better than the high intensity groups in this category.
Why is this important? The measure that the researchers used is called the disposition index (DI) and it has been shown to be a valid predictor of the onset of type 2 diabetes. Behaviors which markedly improve the DI would (hopefully) decrease the likelihood of actually progressing from prediabetes to the disease itself. The problem here is that we don’t really know if the DI will continue to predict disease onset under these conditions.
While this is not exactly a news flash, it is good to note once again that exercise is one of the BEST things you can do for yourself. It is comforting to know that you don’t have to run a marathon to get the best results. Unless, of course, you want to run a marathon. Go for it.