Exercise and diet modification are commonly recommended approaches for reducing type II diabetes risk factors such as obesity, impaired glucose tolerance, and insulin resistance. A sedentary lifestyle has been associated with decreased insulin sensitivity and increased fasting state insulin.
A study looked at the effects of calorie restriction and exercise on glucose and insulin concentrations in 60 sedentary overweight men aged 20 to 50 years old. Subjects were divided into two groups; restricted caloric intake (1000-1500 calories/day) and non-restricted caloric intake, and then further sub-divided into light intensity (minimal exercise) or vigorous intensity (30 minutes of exercise three times a week of cycling at 70% maximum heart rate). The results showed that vigorous exercise alone (in the absence of calorie restriction) decreased fasting glucose by 13% and reduced glucose and insulin resistance by 20%. The results also showed that calorie restriction resulted in a 40% reduction in the insulin resistance and vigorous exercise and calorie restriction were additive in reducing the insulin resistance. In conclusion both calorie restriction and vigorous exercise independently and additively reduce glucose and insulin concentrations in overweight and sedentary men (Cox et al., 2004. American Journal of Clinical Nutrition. 80, 308-316).
Another study looked at the effects of a lifestyle-intervention program on glucose tolerance in 102 overweight individuals. The subjects were divided into two groups; one receiving regular (one hour per week) diet advice and encouagement to lose weight and to increase their physical activity, and another that received only a brief information session on the benefits of a healthy diet and exercise. The subjects were followed for one year and glucose tolerance was measured before and after the experiment. The results showed that after one year weight loss was higher and blood glucose concentration decreased significantly in the intervention group. It was concluded that weight loss and increased physical fitness were the most important determinants of improved glucose tolerance and insulin sensitivity. It is apparent that a lifestyle-intervention program involing diet and exercise modifications is effective in improving glucose tolerance (Mensink et al., 2003. International Journal of Obesity 27, 377–384).
It is evident that exercise alone can improve insulin sensitivity and glucose utilization. The value of exercise in the treatment and prevention of type 2 diabetes cannot be understated, and thus in addition to diet and lifestyle modifications it must be incorporated in the treatment of type 2 diabetes.