What causes insulin resistance?

Because insulin resistance tends to run in families, we know that genes are partly responsible. Excess weight also contributes to insulin resistance because too much fat interferes with muscles' ability to use insulin. Lack of exercise further reduces muscles' ability to use insulin.

Many people with insulin resistance and high blood glucose have excess weight around the waist, high LDL (bad) blood cholesterol levels, low HDL (good) cholesterol levels, high levels of triglycerides (another fat in the blood), and high blood pressure, all conditions that also put the heart at risk. This combination of problems is referred to as the metabolic syndrome, or the insulin resistance syndrome (formerly called Syndrome X).

Metabolic Syndrome

Metabolic syndrome is defined by the National Cholesterol Education Program as the presence of any three of the following conditions:

• excess weight around the waist (waist measurement of more than 40 inches for men and more than 35 inches for women)
  
  
• high levels of triglycerides (150 mg/dL or higher)
  
  
• low levels of HDL, or "good," cholesterol (below 40 mg/dL for men and below 50 mg/dL for women)
  
  
• high blood pressure (130/85 mm Hg or higher)
  
  
• high fasting blood glucose levels (110 mg/dL or higher)
  
  

Source: National Cholesterol Education Program, Third Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), National Heart, Lung, and Blood Institute, National Institutes of Health, May 2001.

Note: Other definitions of similar conditions have been developed by the World Health Organization and the Association of Clinical Endocrinologists.

source: http://diabetes.niddk.nih.gov/dm/pubs/insulinresistance/index.htm