Effects of Low and Moderate Fat Diets on Lipids, Inflammation and Vascular Reactivity in the Metabolic Syndrome
Condition: Metabolic Syndrome X; Dyslipidemias
MeSH terms: Metabolic Syndrome; Dyslipidemias; Syndrome
Study type: Interventional

Summary: 
      The metabolic syndrome consists of five concurrent conditions which increase risk of heart
      disease, stroke, and diabetes. Persons with the metabolic syndrome usually have high
      triglyceride and low HDL levels and are overweight. Low fat, high carbohydrate diets may not
      provide the same cholesterol-lowering benefits to obese individuals as they do to non-obese
      individuals. The purpose of this study is to compare the effects of a low fat, high
      carbohydrate diet versus a moderate fat, moderate carbohydrate diet on the heart, blood
      vessels, and cholesterol levels in individuals with metabolic syndrome.
    

Detailed description: 
      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.
    

Intervention name(s): Moderate Fat and Moderate Carbohydrate Diet; Low Fat and High Carbohydrate Diet
Intervention type(s): Behavioral; Behavioral
Intervention description(s): 40% allowable fat diet (less than or equal to 7% saturated fat) consumed for 1 or 5 months; 20% fat diet (less than or equal to 7% saturated fat) consumed for 1 or 5 months
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Treatment
Keywords: Obesity; Hypertension; Insulin Resistance