Diabetes Mellitus: Present and Future Preventive Strategies—Part I This is the first in a continuing series of articles
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These latter changes were noted despite these patients still being obese, with a mean BMI of 33 kg/m2. Insulin sensitivity improved in proportion to weight loss following gastric bypass surgery; biliopancreatic diversion, predominantly a malabsorption-promoting procedure, led to normal insulin sensitivity long before body weight changes were significantly improved. The authors concluded that selective nutrient absorption and gut hormones might be associated with the insulin insensitivity associated with obesity.5
Exercise increases the amount of glucose taken up by muscles, and thus plays an important role in blood sugar regulation. It also helps to increase caloric expenditure and help one lose weight. Even prior to the discovery of insulin by Banting and Best, exercise was recommended as a way to control blood glucose.6 The following are arguments that have been used to support a relationship between exercise and improved insulin sensitivity:
• Older athletes have a lower insulin response to glucose challenge than nonathlete controls;
• Aerobic conditioning of previously inactive obese subjects improves fitness as it lowers the plasma insulin response to glucose, despite no change in glucose tolerance;
• Several days of forced physical inactivity in previously active men led to a loss of glucose tolerance and an increase in the plasma insulin response to an oral glucose challenge;
• Highly trained athletes have been shown to have an increased rate of glucose disposal using glucose clamp techniques; and
• Glucose disposal is highly correlated with maximal exercise capacity (VO2max)
Although data suggest that physical activity promotes glucose uptake by enhancing insulin sensitivity, loss of this sensitivity occurs within a few days of physical inactivity, despite maintaining maximal aerobic capacity. Insulin sensitivity may also be closely related to the depletion of muscle glycogen. It has been reported that even a single session of exercise in men with type 2 diabetes mellitus who are unfit is associated with increased insulin sensitivity and reduced overnight endogenous glucose production.
There is a wealth of epidemiologic evidence to support a relationship between physical inactivity and diminished glucose tolerance; it remains unclear whether exercise is responsible for this difference or some other factor associated with the exercise, such as a change in weight or body composition. In a study of more than 5000 former college athletes and nonathlete, age-matched controls, former college athletes were noted to be leaner than nonathletes up to the age of 70. They were also more physically active, with 74% currently exercising compared to 56% of controls, and had a lower prevalence of diabetes mellitus.7 Another study reported that those individuals in the highest tertile of physical activity had half the prevalence of impaired glucose tolerance (IGT) as those in the lowest tertile.
In the Second National Health and Nutrition Examination Survey, a cross-sectional study that examined the relationship between IGT and a variety of other variables, 15,000 individuals were evaluated; 6.6% were diagnosed with diabetes mellitus, 97% of whom had type 2 disease. An additional 11.2% were identified as having IGT. Physical inactivity was considered to be a risk factor for IGT, independent of other contributing variables including age, past obesity, and family history. Those with IGT were 1.5 times more likely to report little or no exercise, and were twice as likely to have a resting heart rate over 100 beats/min.
A study of more than 1200 physician marathon runners and 683 nonrunning physician controls reported that runners were leaner and had a 40% lower prevalence of diabetes mellitus than non-running controls. They were also one-fifth as likely to have hypertension and less likely to be smokers and have hypercholesterolemia.
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