Insulin resistance is a condition in which the body's mechanism for signaling to the cells when glucose, or blood sugar, is present in the bloodstream is defective. Insulin resistance is a serious condition, as it is a risk factor for Type 2 diabetes, a condition in which a larger number cells can no longer use glucose as a fuel. Doctors commonly prescribe blood glucose medications and a low-carb diet to control insulin resistance.
Blood Glucose
When a healthy individual eats a meal that contains carbohydrates, the carbohydrates convert to glucose in the digestive system, and the glucose enters the bloodstream through the wall of the intestinal tract. The pancreas responds by producing insulin. When insulin binds to cell receptors, or binding sites, on their surfaces, this signals to the interior of the cells that glucose is present in the bloodstream. The cells then embed glucose transporters into their membranes and transport glucose into the cells. The cells can use the glucose for immediate energy or store it as fat or glycogen, the stored form of blood sugar.
Insulin Resistance
In insulin resistance, the pancreas keeps producing insulin in response to glucose that enters the bloodstream from the digestive system. When insulin binds to insulin receptors, however, the signal does not transfer properly to the interior of the cell. So, the affected cells do not embed glucose transporters into the cell membrane. As a result, glucose accumulates in the bloodstream, and the affected cells are starving, as they don't get enough energy.
Muscle Insulin Resistance
Insulin resistance normally starts out as partial. A common form of insulin resistance is resistance in the skeletal muscles. The most common symptom of this form of insulin resistance is muscle fatigue. When a person suffers from insulin resistance in the skeletal muscles, the muscles absorb glucose at a slower rate than in healthy individuals. Excess glucose accumulates in the bloodstream. In an effort to lower blood sugar levels, the liver converts the excess glucose to fat, which results in rapid weight gain around the belly.
Brain Insulin Resistance
Unlike most of the body's cells, which can use the building blocks of protein, fat and carbohydrate as a fuel, the brain can only use glucose or ketone bodies, a byproduct of fat metabolism. The brain prefers glucose to ketone bodies, as the ketone bodies are harder to metabolize than glucose. When the insulin receptors on brain cells do not signal to the interior of the brain cells that glucose is available, the cells cannot use glucose, but they are also unable to use ketone bodies as an alternative energy source. So, these brain cells do not get sufficient energy. Though there is some controversy about this issue, this sort of brain starvation may be a factor in the development of degenerative diseases, such as Alzheimer's disease.
References
- National Diabetes Information Clearinghouse (NDIC): Insulin Resistance and Prediabetes
- "PNAS"; The Role of Skeletal Muscle Insulin Resistance in the Pathogenesis of the Metabolic Syndrome; Kitt Falk Petersen, et al.; July 2007
- "PNAS"; Role for Neuronal Insulin Resistance in Neurodegenerative Diseases; Markus Schubert, et al.; March 2004
- University of California, San Diego: Muscle Physiology
