It’s time for another installment in my Inactivity and Metabolic Health Series! For your consideration today is the small but interesting study from the Washington University School of Medicine in St. Louis, Missouri:
Improvement in Glucose Tolerance After 1 Wk of Exercise in Patients With Mild NIDDM
There were only 10 middle aged men in this study. While it’s true that studies this small can’t automatically be extrapolated to apply to everyone, what I’m trying to show people through this series is that each small study serves as a data point in a broader constellation of evidence. There is quite a vast body of evidence that inactivity is a primary driver of metabolic dysfunction, and even though no single study can ever be taken of irrefutable evidence of anything, when dozens, hundreds or even thousands of studies all show similar results across population groups, one must sit up and take notice. You can prove pretty much anything if a single study is your litmus test (broccoli will kill you! I saw a study!). What does the weight of evidence say, though?
On to the study. 7 of the men in this study had mild NIDDM (non-insulin dependant diabetes mellitus) and 3 had impaired glucose tolerance (ie, they hadn’t been diagnosed with NIDDM yet but had the precursors). They were instructed not to change their diets over the course of the study, and kept food logs that were analyzed by a dietician to ensure that study results weren’t confounded by diet changes. They were given an initial Oral Glucose Tolerance Test, a physical exam (including blood lipid panel), and a maximal treadmill exercise test before study onset to establish baseline values.
The subjects engaged in a 7 day exercise program consisting of 50-60 minutes on a treadmill or ergometer, working at 60-70% of their maximum heart rate. On the 8th day they were given a second OGTT and exam. On the 9th day they were given a second treadmill test.
VO2 max, body fat percentage and weight all remained unchanged after the 7-day exercise program, so those factors did not confound the results. There was a 36% decrease in plasma glucose, a 32% decrease in plasma insulin concentrations, and a 32% decrease in triglycerides.
What is notable here is that the subjects’ insulin response to a glucose load (from the OGTT) was significantly lower than it had been before the study. What this means: their bodies released less insulin in response to the same amount of sugar after exercising for 7 days. This is significant to the Great Sugar Narrative that holds that sugar is the driver of insulin production and release. Clearly exercise is a pertinent factor here that is ignored by the sugar-causes-diabetes contingent. Exercise can mitigate the insulin response to sugar.
Plasma glucose also decreased, even with a decreased insulin response, which indicates that the cells ability to respond to insulin also improved. From the study:
“The results of this study show that regularly performed vigorous exercise can result in a significant improvement in glucose tolerance in some patients with mild NIDDM. This improvement occurred despite a significantly smaller increase in plasma insulin levels. it appears that the improvement in glucose tolerance was due to a decrease in resistance to insulin.”
Also of note: triglycerides decreased 32% with no change in diet.
Bottom line: exercise reduces insulin response AND makes the body more sensitive to the action of insulin. Exercise does lots of other groovy things too.