Insulin resistance is often referred to as pre-diabetes, because it precedes the development of type II diabetes.
What is Insulin Resistance?
Insulin is a hormone secreted by the pancreas. One of the major functions of insulin is to stimulate glucose uptake into tissues for utilization. Transport of glucose into tissue keeps blood glucose levels within a specific range of ‘normal’ values. With insulin resistance, tissues become resistant to the effects of insulin, which means the pancreas must produce more insulin to maintain normal blood glucose levels. Over time, the pancreas no longer produces sufficient amounts of insulin, which results in high blood glucose levels and a probable diagnosis of type II diabetes. In fact, several prospective studies have concluded that insulin resistance is the best predictor of whether a person will go on to develop diabetes.
How does the Glucose Breath Test for Insulin Resistance work?
Insulin stimulates the uptake of glucose into tissues. Approximately 50% of ingested glucose is metabolized to carbon dioxide and water. The test measures the expired carbon dioxide before and after ingestion of a stable C-13 universally labeled glucose (non-radioactive) compound. Patients with normal insulin function exhale a greater percentage of C-13 labeled carbon dioxide because more C-13 labeled glucose is transported to tissue by insulin. The glucose in tissue is eventually metabolized to C-13 carbon dioxide and water and exhaled. Insulin resistant patients exhale less C-13 carbon dioxide because resistance to the effects of insulin reduces the transport of C-13 labeled glucose into tissues, and therefore less C-13 carbon dioxide is produced.
In other words, the C-13 glucose breath test is a function test for insulin resistance: it measures how well insulin functions at delivering glucose into tissues. If insulin is functioning well, more glucose is delivered to the tissues and the result is more C-13 carbon dioxide production. If insulin is functioning poorly, less glucose is delivered to tissue and the result is less C-13 carbon dioxide production.
Diseases and Conditions Associated with Insulin Resistance
Insulin resistance is strongly correlated with the development of diabetes. Over an 8 year period, patients in the highest quartile for fasting insulin levels (another measurement of insulin resistance) were over 5 x more likely to develop diabetes than those in the lowest quartile.
Approximately 50% of hypertensive patients have insulin resistance. There is also evidence that insulin levels have a direct effect on lowering blood pressure. Over an 8 year period, patients in the highest quartile for fasting insulin levels were approximately twice as likely to develop hypertension as those without.
High insulin levels, independent of blood glucose levels and other risk factors like triglycerides, have show to increase in the risk of cardiovascular disease
Polycystic Ovarian Syndrome (PCOS)
Women with PCOS have approximately 7 x greater likelihood of having impaired glucose tolerance (a measurement of insulin resistance) than women without PCOS.