Effects of Low and Moderate Fat Diets on Lipids, Inflammation and Vascular Reactivity in the Metabolic Syndrome

• Non-HDL cholesterol [ Time Frame: Measured at screening, baseline, at the beginning and end of the 1st and 2nd diet periods, and at the end of each month for four months during the diet extension ] [ Designated as safety issue: No ]
  
• C-reactive protein [ Time Frame: Measured at the beginning and end of the 1st and 2nd diet periods and at the end of the four month diet extension ] [ Designated as safety issue: No ]
  
• Brachial artery reactivity [ Time Frame: Two measurements are done at the beginning and end the 1st and 2nd diet periods and at the end of the four month diet extension ] [ Designated as safety issue: No ]
  

The Metabolic Syndrome is characterized by elevated insulin levels, excess body fat in the waist, and elevated levels of glucose and blood pressure, and dyslipidemia. Dyslipidemia in the Metabolic Syndrome is characterized by high levels of triglycerides, low levels of HDL cholesterol, and above average LDL and non-HDL cholesterol. Individuals with elevated LDL cholesterol have traditionally been advised to follow a low fat, high carbohydrate diet. However, research has shown that this diet does not adequately regulate cholesterol levels in individuals with dyslipidemia. A diet consisting of more moderate amounts of fats and carbohydrates may be more beneficial for individuals with the dyslipidemia of the metabolic syndrome. The purpose of this study is to compare the effects of a diet moderate in fat and carbohydrate versus a low fat, high carbohydrate diet on the cholesterol levels, inflammatory factors and vascular response in individuals with metabolic syndrome.

During the initial screening period, participants follow an American Heart Association (AHA) Step 1 diet and cholesterol levels are tested for eligibility under the criteria of the Metabolic Syndrome. Before being randomized, eligible participants have a frequently sampled intravenous glucose tolerance test (FSIVGTT), an abdominal CT scan to measure fat content in two locations and two brachial artery reactivity tests. The FSIVGTT provides information about whether participants are insulin sensitive or insulin resistant. The CT scan measures the fat content in the abdomen and the liver. The brachial artery reactivity tests measure blood flow through the brachial artery in the arm.

This 7-month study consists of two 1-month feeding periods, a rest month between the two feeding periods and a 4-month follow-up diet in a free-living setting. In Month 1, participants are randomly assigned to follow either a moderate fat, moderate carbohydrate diet or a low fat, high carbohydrate diet. Participants receive prepared food at study visits twice a week. Weight and vital signs are measured at each study visit, and blood is collected at baseline, and Weeks 3-1/2 and 4. A brachial artery reactivity test, using an ultrasound to measure artery size and blood flow in the arm, is performed twice in Week 4. In the Month 2 rest period, participants follow an AHA Step 1 diet at home. In Month 3, participants switch to the other diet and all study procedures and evaluations are repeated as in Month 1. During the following Months 4 through 7, participants continue following the second assigned diet, but are responsible for preparing their own food. They meet with a dietician once a week for 1 month to learn how to prepare meals at home. During this 4-month period, blood collection, vital sign measurements, and review of medical history and diet continue at monthly visits. At the end of Month 7, participants again undergo two brachial artery reactivity tests.

As of October, 2010, 148 were screened with 71 eligible to be randomized. Seven discontinued prior to completion and 64 completed the 7 month study. The intervention is complete and analyses are ongoing.