Insulin is a hormone that is normally released by the beta cells of the pancreas. When a person’s pancreas cannot produce enough insulin to sustain good health, insulin can be injected into the body with a needle or infused with a pump.
One of the main functions of insulin is to lower blood glucose levels by enabling glucose to enter the cells of the body, where it is used for energy or stored for future use. A person who is insulin-sensitive needs only a relatively small amount of insulin to keep blood glucose levels in the normal range and to keep the body’s cells supplied with the glucose they need. A person who is insulin-resistant, on the other hand, needs a lot more insulin to get the same blood-glucose-lowering effects.
Insulin resistance is associated with numerous health risks. For one thing, it causes hyperinsulinemia, or high circulating insulin levels, which may be directly damaging to blood vessels. Hyperinsulinemia is also associated with high blood pressure, heart disease and heart failure, obesity (particularly abdominal obesity), osteoporosis (thinning bones), and certain types of cancer, such as colon, breast, and prostate cancer. In contrast, having low circulating insulin levels is associated with greater longevity; most centenarians without diabetes have low circulating insulin levels.
Insulin resistance is a hallmark of Type 2 diabetes, but it can occur in Type 1 diabetes as well. In fact, there is a growing number of people who are said to have “double diabetes” because, in addition to having Type 1 diabetes, they also have the insulin resistance characteristic of Type 2.
The good news is that you can lower your level of insulin resistance — and raise your level of insulin sensitivity — by modifying your lifestyle choices, particularly your exercise and eating choices, regardless of the type of diabetes you have.
How physical activity helps
Physical activity has a significant positive effect on insulin sensitivity. Indeed, it may have the biggest effect of any measure you could take to improve your insulin sensitivity. Any type of physical activity has the potential to make your insulin work better, and combining aerobic activities — such as brisk walking, swimming, and cycling — with resistance training, or weight training, appears to have the greatest effect. Aerobic activities burn more calories (and glucose) per session, but resistance training builds muscle, which is what burns glucose during exercise, so having more is better.
Numerous studies bear out the value of physical activity and exercise in improving insulin sensitivity. In a study of lean, sedentary, young adult women (ages 18–35), both six months of thrice-weekly aerobic training and six months of resistance training improved glucose use in the body.
In another study, sedentary, insulin-resistant, middle-aged adults who engaged in 30 minutes of moderate walking three to seven days per week for six months succeeded in reversing their insulin resistance — without changing their diets or losing any body weight (although their body proportions of fat and muscle likely changed for the better).
In a study of older adults in their 70’s, low- to moderate-intensity “walking” on a mini-trampoline for 20–40 minutes four days per week over a four-month period enhanced their glucose uptake by cells without any additional insulin release by the pancreas or loss of abdominal fat.