Study of the Effect of a Very-Low-Carbohydrate Diet on Energy Expenditure
Condition: Obesity; Appetite; Healthy Volunteers
MeSH terms: Obesity
Study type: Observational

Summary: 
      Background:

      - Popular weight loss plans often restrict carbohydrates or fat. Research shows that
      very-low-carbohydrate (ketogenic) diets lead to greater weight loss than low-fat diets.
      Researchers want to know if eating fewer carbohydrates changes the number of calories the
      body uses. They also want to know how a ketogenic diet affects hunger, hormones, and food
      preferences.

      Objectives:

      - To better understand how the body responds to different diets.

      Eligibility:

      - Men 18 to 50 years old who are healthy but overweight.

      Design:

        -  Participants will have 3 screening visits:

             1. Medical history, physical exam, blood test, and EKG. They will eat during the
                visit.

             2. For the week before the visit, participants will wear physical activity monitors
                daily. They will record everything they eat and sample the special diet. At the
                visit, they will receive an EKG and heart rate test while biking for 30 minutes.

             3. For the week before the visit, participants will wear the physical activity
                monitors. They will eat all their meals from the special diet that will be
                provided. At the visit, they will answer questions and bike for 60 minutes.

        -  After screening, for 1 week, participants will visit the clinic daily to receive that
           day s food. They will not eat or drink anything else except water.

        -  Then participants will stay at the clinic for 8 weeks. They cannot leave but can have
           visitors. Participants will wear physical activity monitors, bike daily, and follow
           different diets. Tests will be given daily, and may include weighing, X-rays, and blood
           and urine tests. They will spend several days in a monitored room to test oxygen and
           carbon dioxide.
    

Detailed description: 
      Popular weight loss strategies often prescribe targeted reduction of dietary carbohydrate or
      fat. Recent clinical trials in obese subjects have found that low-carbohydrate diets result
      in greater weight loss compared with low-fat diets on a time scale of months when diet
      adherence was likely the highest. One hypothesis regarding the mechanism of improved weight
      loss with low carbohydrate diets is that such diets significantly modify the body s hormonal
      milieu to influence metabolic regulation and energy expenditure. Low-carbohydrate diets may
      thereby offer a metabolic advantage over low fat diets. In addition, low-carbohydrate diets
      may also decrease hunger or increase satiety compared to low-fat diets.

      Determining the mechanism whereby one diet leads to greater weight loss than another is
      hampered by the inability to accurately measure food intake or physical activity in an
      outpatient setting. Thus, an inpatient feeding study lasting many weeks is required to
      accurately measure energy balance differences between isocaloric diets that differ in
      macronutrient composition. In this pilot multicenter cross-over study in 16 overweight and
      class I obese men, we will measure changes in energy expenditure in response to 4 weeks of
      inpatient feeding of a eucaloric, very low carbohydrate, ketogenic diet (5% Carbohydrate, 15%
      Protein, 80% Fat) immediately following an inpatient period of at least 4 weeks of consuming
      an energy balanced standard American diet (50% Carbohydrate, 15 % Protein, 35% Fat).
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        We will study the magnitude and variability of energy expenditure changes in response to a
        eucaloric ketogenic diet subsequent to a standard energy- and macronutrient-balanced diet
        in overweight and class I obese adult male volunteers
      
Keywords: Energy Expenditure; Obesity; Carbohydrate; Fat; Ketones; Natural History