Effect of Diet on Vascular Disease: Study of African American & Caucasian Women

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For this study we will enroll 96 women (48 African American and 48 Caucasian women). We are enrolling women between the ages of 18 and 64 years. The study will involve several outpatient visits to the NIH Clinical Center. The first visit will be a screening to determine eligibility. At the second visit a test will be performed to measure insulin resistance. This test is called a frequently sampled intravenous glucose tolerance test. The third visit will be for the test meal. Before and at 2, 4 and 6 hours after the meal, blood will be drawn and vascular function measured. Vascular function is determined by taking blood pressure and then measuring blood flow in the arm with ultrasound. It is possible that individual differences in diet could affect the results of the vascular study on the day of the test meal. Therefore for 7 days prior to the test meal, the NIH Clinical Center will provide to each participant all their meals in the form of either trays or meals in a box. These meals will consist of the typical American diet and be 33% fat, 15% protein and 52% carbohydrate. In designing these meals, the dietician will take into account individual food preferences. Twenty-six women (16 African American and 16 Caucasian) have now completed the study. Enrollment and analysis of data already collected is underway. Our early findings are that African American women are more insulin resistant and hyperinsulinemic than white women. In addition, African American women have lower TG and lower apoCIII levels both fasting and postprandially than white women. Hyperinsulinemia in African American women is a major factor accounting for high free fatty acid clearance and low TG levels. In addition, because hyperinsulinemia is responsible for greater clearance of free fatty acids, this may be a major factor explaining higher degree of peripheral fat and lower visceral adiposity in African American women than white women. ApoCIII which has not been previously studied postprandially in African-American women is lower in African American than white women. ApoCIII inhibits activity of lipoprotein lipase, the enzyme which clears TG from the circulation. Therefore while high apoCIII is responsible for high TG levels and low apoCIII is at least one factor explaining low TG levels in African American women.