Lack of exercise and obesity are the two major environmental variables for insulin resistance (and type 2 diabetes).
The rising prevalence of type 2 diabetes is attributable, in part, to increased insulin resistance in our population as we get more obese and exercise less. Insulin resistance can be lowered within a few days of beginning a low-calorie diet, even before significant weight reduction occurs (American Diabetes Association, 1998). Subsequent weight loss improves insulin sensitivity even more. Exercise, especially strenuous exercise, lowers insulin resistance, albeit this benefit fades fast (within 5 days) if exercise is discontinued (American Diabetes Association, 1998).