Exercise training improves insulin sensitivity.19 Patients with suspected insulin resistance should be advised to increase their level of physical activity. Even regular, sustained, moderate increases in physical activity, such as daily walking, can substantially decrease insulin resistance.20 This is compatible with the standard recommendation that everyone should accumulate at least 30 minutes of moderate-intensity physical activity on most or, even better, all days of the week.21
Hypocaloric Diet and Weight Reduction
Insulin sensitivity improves within a few days of caloric restriction, before any significant weight loss occurs.13 Weight reduction leads to further improvement. The amount of weight loss needed for sustained decreases in insulin resistance is still unclear. In obese women without diabetes, weight loss of approximately 15 percent has been linked to significantly lower insulin levels.22 Regaining even a modest amount of the lost weight, however, with a body weight that was still 10 percent below starting values, resulted in an increase in insulin levels to baseline. The women in this study were very obese (mean BMI: 36.4 kg per m2) and remained obese even with the loss of 15 percent of body weight (mean BMI: 30.5 kg per m2). The implication is that all obese patients should be encouraged to attain a healthy body weight. This can be accomplished and sustained through dietary modification and exercise–a recommendation that is easy to make, of course, but difficult to follow.
The amount of dietary fiber consumed is inversely related to insulin levels.23 This observation may explain the lower incidence of hypertension, hyperlipidemia and cardiovascular disease among people with diets high in fiber. A diet high in natural sources of fiber (e.g., whole grains and vegetables) helps combat insulin resistance.
Metformin has been successfully used for some time to treat diabetes. It increases insulin sensitivity,24 as does the new thiazolidinedione class of drugs.25 These drugs are not labeled for treatment of isolated insulin resistance. Pending more evidence, the American Diabetes Association does not recommend drug therapy for the treatment of insulin resistance in the absence of diabetes.2
Metformin, diet and exercise are being studied in the National Institutes of Health*sponsored Diabetes Prevention Program.26 Although the outcome being studied is type 2 diabetes, these interventions clearly improve insulin sensitivity. At this time, clinicians should make it a priority to aggressively identify patients with possible insulin resistance and assist them in making appropriate lifestyle modifications.