How physical activity and other factors affect insulin action.
By Sheri Colberg-Ochs, PhD
Any type of physical training can make your insulin work better. If you’re physically trained, you will generally have a heightened sensitivity to insulin—but why? It appears that the answer varies according to the type of training you do. For instance, in lean but sedentary young adult women (ages eighteen to thirty-five) engaging in six months of thrice weekly either endurance (aerobic) or resistance (weight) training, both forms of training improved their glucose use, but by different mechanisms.
Weight training apparently results in enhancements in your muscle mass, allowing for greater overall glucose uptake. While endurance training does not increase your muscle mass as much, it does enhance your muscular uptake of blood glucose without changes in body weight or abdominal fat.
What if you’re older or overweight? Training will still work for you. Sedentary, insulin-resistant, middle-aged adults engaging in 30 minutes of moderate walking three to seven days per week for six months succeeded in reversing their prediabetic state—without changing their diets or losing any body weight (although their body proportions of fat and muscle likely changed).
In older adults (average of 72 years), all it took was low- to moderate-intensity “walking” on mini-trampolines for 20 to 40 minutes four days per week over a four-month period to enhance their glucose uptake without any additional insulin release or loss of abdominal fat. If you’re young but obese, you’re still in luck. Studies have shown that, regardless of your age, exercise training can improve your insulin action within just one week of training without weight loss or a true training adaptation in muscle.
In addition to walking, you might want to do some weight training as well to further improve your sensitivity to insulin and better control your diabetes. In people with type 2 diabetes, four to six weeks of moderate intensity (40 to 50 percent of maximal) resistance training improved their insulin sensitivity by 48 percent without causing any significant changes in their body fat or muscle mass.
Similarly, newly diagnosed type 2 diabetic men who did 16 weeks of “progressive” resistance training (the resistance lifted was increased over time) just twice a week gained muscle mass, lost body fat (particularly in the abdominal region), and greatly enhanced their insulin action—all despite a 15 percent increase in the amount of calories they consumed.
Likewise, if you’re an older, type 2 diabetic woman, the combination of aerobic and resistance training may afford even greater improvements in your insulin action and a more significant decrease in your abdominal fat than aerobic training alone, with increased muscle mass to boot.
It appears that scientists may have jumped to the wrong conclusion when they decided to blame fat cells alone for everything that ails you, including insulin resistance and type 2 diabetes. Granted, the vast majority of insulin-resistant people (with prediabetes or type 2 diabetes) are indeed overweight, but not all people who are overweight are insulin resistant.
Furthermore, you can reverse prediabetes without a significant loss of body fat simply by implementing positive changes in your exercise and dietary habits. As shown in the following table, many factors besides weight loss can improve your body’s insulin sensitivity and, consequently, reverse prediabetes or improve diabetes control.
Don’t try just adding some more exercise in. For optimal results, try to improve your body’s insulin action by several of these means as their effects are likely to add together to result in a greater overall effect.
Other Factors That Can Improve Insulin Sensitivity:
•Regular aerobic and resistance exercise
•Muscle mass gain
•Loss of body fat—particularly intra-abdominal (visceral) fat, extra fat stored in the liver, and possibly some of the excess fat in muscles
•Improved blood glucose control (and avoidance of highs and lows)
•Reduced levels of circulating free fatty acids (one type of fat in blood)
•Reduction in low-level, systemic inflammation (via suppression of TNF-alpha)—mainly accomplished through physical activity and antioxidants
•More effective action of leptin, a hormone released by fat cells, causing reduced food intake
•Reduction in mental (anxiety, depression) and/or physical (illness, etc.) stressors
•Decrease in circulating levels of cortisol, a hormone released in response to all forms of stress (i.e., physical and mental)
•Increased testosterone levels in men
•Intake of more dietary fiber, less saturated and trans fat, and fewer highly refined foods with a high glycemic effect
•Daily consumption of a healthy breakfast
•Lower caffeine intake
•Adequate sleep (seven to eight hours a night for most adults)
•Effective treatment of sleep apnea
•Use of insulin-sensitizing oral medications (like Avandia or Actos)
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