The Effect of Dietary Sitosterol on Blood Sugar and Cholesterol

This study will determine if dietary supplements of sitosterol (a plant cholesterol commonly found in vegetables) can modify blood sugar and cholesterol levels and reduce the stiffness of the blood vessels in people with an abnormal copy of a gene that causes sitosterolemia. People who carry only one copy of the abnormal gene are healthy but have increased blood levels of sitosterol. People with two abnormal copies of the gene have increased levels of sitosterol and have an increased risk of heart attack. This condition is called sitosterolemia. Although extremely rare in the general population, up to 4% of the Amish carry an abnormal copy of this gene. People of Amish background who are 18 years of age or older and in whom one person carries one copy of the abnormal gene that causes sitosterolemia and the other does not have an abnormal gene may be eligible for this study. Subjects must be of the same sex and within 5 years of age of each other. During two periods of one month each participants receive pills containing sitosterol and then a special diet and meal supplements to change the levels of sitosterol in the diet. During only one of the two study periods, subjects receive sitosterol supplements in the pills for one month and then for 10 days in the diet. At the end of each study period, subjects come to the NIH Clinical Center for one day for the following tests:

• Measurements of height, weight, blood pressure and heart rate.
• Adipose (fat) tissue biopsy. A small piece of fat from under the skin of the abdomen is removed to examine how sitosterol affects fat tissue and its ability to process sugar and fat.
• Indirect calorimetry. A plastic transparent hood is placed over the subject s head to collect the air that is breathed for about one-half hour to study how the body uses sugar to generate energy.
• Endothelial vascular function. An ultrasound picture of a blood vessel in the forearm is taken and a blood pressure cuff is inflated around the arm to measure the vessel s ability to stretch.
• Intravenous glucose tolerance test: A small plastic tube is placed in a vein in each arm. Then over one minute the subject receives glucose through one of the tubes. Twenty minutes later the subject is given a small amount of insulin through the same tube. Blood samples are drawn through the tube in the other arm at frequent intervals for 3 hours. This test measures how sitosterol affects how the body processes sugar.
• DEXA scan. The subject lies on an x-ray table for 20 minutes during the scan, which measures total body fat.