by Dr. Sheri Colberg, Ph.D., FACSM
Having ineffective insulin action, or an insulin resistant state, is associated with numerous health risks, such as hyperinsulinemia, or high levels of insulin in the blood, that may damage blood vessels and contribute to arterial plaque formation and heart disease. A decrease in your insulin action is also directly related to higher levels of systemic inflammation, which means that your body is releasing more of certain substances called cytokines. High insulin levels and inflammation are also associated with high blood pressure, obesity (particularly intra-abdominal), osteoporosis, and common cancers like colon, breast, and prostate.
In contrast, most athletic individuals have lower levels of insulin and require less insulin release for carbohydrate and other food intake, meaning that their bodies are very sensitive to insulin and their risk for these health problems is much less. Having low fasting insulin levels (assuming it is not due to a deficiency) is associated with greater longevity, as demonstrated by the fact that most 100-year-olds without diabetes exhibit this trait. What’s more, exercise reduces systemic inflammation without weight loss, reducing the risk for all metabolic diseases.
Almost 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. For instance, in lean but sedentary young adult women (ages 18 to 35 years) engaging in six months of thrice weekly aerobic or resistance training, both forms of training improved their glucose use, but by different mechanisms. Resistance training results in enhancements in your muscle mass, allowing for greater overall glucose uptake. While aerobic training generally does not increase muscle mass as much, it does enhance muscular uptake of blood glucose without changes in body weight or abdominal fat.
The effects of aerobic exercise on insulin action usually start to decline within 1-2 days, however, and regular aerobic activity is essential to keeping it higher. Increasing your overall muscle mass may have a more lasting effect by allowing for greater glucose uptake and storage in muscle (an insulin-sensitive tissue) and increasing the total amount of glucose you can dispose of through glycogen storage. Muscles have a limit to how much they can store, and having more muscle mass results in a greater potential storage capacity.
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. 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.
Myriad 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 or 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.
Factors That Can Improve Insulin Action
- 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 triglycerides and free fatty acids (fats in blood)
- Reduction in low-level, systemic inflammation (with physical activity and antioxidants)
- More effective leptin action (hormone released by fat), causing reduced food intake
- Reduction in mental (anxiety, depression) and/or physical (illness, etc.) stressors
- Control of physical (illness, etc.) stressors
- Decrease in circulating levels of cortisol (released by physical and mental stressors)
- Increased testosterone levels in men
- Intake of more dietary fiber, less trans fat, and fewer highly refined foods
- Daily consumption of a healthy breakfast
- Adequate dietary intake of key vitamins and minerals, such as magnesium
- 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)
As a leading expert on diabetes and exercise, I recently put my extensive knowledge to use in founding a new information web site called Diabetes Motion (www.diabetesmotion.com), the mission of which is to provide practical guidance about blood glucose management to anyone who wants or needs to be active with diabetes as an added variable. Please visit that site and my own (www.shericolberg.com) for more useful information about being active with diabetes.
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