Body Heat Content and Dissipation in Obese and Normal Weight Adults
Condition: Obesity
Study type: Observational

Summary: 
      This study will investigate how different parts of the body lose body heat and will measure
      the heat released by specific areas such as the limbs and abdomen. Animal studies suggest
      that dissipation of body heat may affect energy expenditure, and therefore, body weight. This
      study will explore the relationship between obesity and heat in humans.

      Healthy people 18 years of age and older who are of normal weight or who are obese and who
      are not taking medications for obesity-related medical conditions may be eligible for this
      study. Candidates must have a body mass index (BMI) between 18 and 25 kg/m2 for normal weight
      subjects or a BMI greater than 30 kg/m2 for obese subjects. All candidates must weigh less
      than 300 pounds. Women must have a normal menstrual cycle or be postmenopausal.

      Participants undergo the following procedures in a single day on an outpatient basis:

        -  Medical history, physical examination, blood and urine tests and electrocardiogram.

        -  DEXA and MRI scans of the trunk and limbs to measure the amounts of muscle, bone and fat
           in the body. For the DEXA scan, the subject lies on a table while a very small dose of
           x-rays is passed through the body. For the MRI, the subject lies on a table that is
           moved into a steel cylinder. A magnetic field and radio waves produce images that are
           used to measure fat in the trunk of the body, thighs, and arms.

        -  Infrared photography of hands, front of thigh, and abdomen. A special camera is used to
           measure the heat leaving the body.

        -  Bicycle exercise test. The subject exercises on a stationary bicycle while the heart
           rate, heart rhythm, blood pressure and oxygen consumption are measured. The pedal
           resistance is increased gradually until the subject can no longer exercise and then the
           resistance is gradually decreased for cool-down.

      Participants who qualify for the second part of the study undergo the following procedures
      during a 5-day in-hospital stay:

        -  Temperature measurements. Body temperature is measured in the ear canal. Skin
           temperature is measured with small round adhesive temperature-sensing patches placed on
           the abdomen and limbs for up to 5 days.

        -  Measurement of body radiowaves. A remote sensing device is used to measure microwaves
           that are naturally released from the body.

        -  Infrared photography of hands, front of thigh and abdomen is done several times during
           the study.

        -  Application of mild coolness to hands, thigh and abdomen. The subject's hand is exposed
           to mild coolness first by immersion in cool water, then by a cool-water spray, then by a
           cooled pad placed on the hand, and finally, with a device applied to the hand that cools
           and has a gentle vacuum. The abdomen and thigh are similarly exposed. During each test,
           an infrared camera records how heat is released by the body.

        -  Temperature effects of a "meal." The subject drinks lemon-flavored sugar water to
           measure the body's response.

        -  Bicycle exercise test. The subject exercises on three different occasions. During or
           after some of the tests, mild cooling is applied to the abdomen, front of the thigh, or
           hands.

        -  Measurement of exhaled air (indirect calorimetry). The subject wears a hood that
           collects and analyzes exhaled air for 15- to 30-minute periods.

        -  Photography and videotaping. The subject is photographed and videotaped. The images do
           not include views of any private parts, and the subject's identity is protected.
    

Detailed description: 
      Animal models suggest that dissipation of body heat is an important physiological process
      that may affect energy expenditure, and thus may possibly modulate body weight. It is
      unknown, however, if deficient dissipation of heat can contribute to human obesity, or if
      obesity induces deficits in heat dissipation, and the relationship between obesity and heat
      in humans is largely unexplored.

      We propose to study obese (BMI greater than or equal to 30 kg/m(2)) and normal weight (BMI
      less than or equal to 25 kg/m(2)) adults to determine possible obesity-related differences
      in: 1) regional body temperature heterogeneity (i.e., presence of localized areas of heat
      retention), 2) the extent to which locally retained heat may be co-localized with deep fat
      depots, 3) the effectiveness of specific body loci (e.g., the distal extremities) as
      dissipaters of heat, and 4) the ability of approaches that alter heat dissipation to modify
      deep-body temperature heterogeneity.

      It is hoped that the results of this study will provide preliminary evidence for future
      studies that attempt to facilitate weight loss in obese subjects through effective, guided
      applications of heat management.
    

Keywords: Adipose Tissue; Weight Gain; Overweight; Thermogenesis; Deep Body Temperature; Adult; Exercise