Water Deprivation Protocol
Condition: Obesity
MeSH terms: Obesity
Study type: Interventional

Summary: 
      Background:

      - One area in which obese and lean individuals may be different is how their bodies handle
      water balance and thirst. Studies done in animals suggest that individuals with greater body
      fat may tolerate periods without water better than lean animals. Other research has found a
      link between the ability to tolerate periods without water and increased body weight.
      Researchers are interested in studying whether the ability to tolerate periods without water
      and ability to feel thirst might differ in lean versus obese individuals.

      Objectives:

      - To evaluate the effects of water deprivation and feelings of thirst in lean and obese
      individuals.

      Eligibility:

      - Healthy individuals at least 18 years of age who are either lean (body mass index less than
      26 kg/m(2)) or obese (body mass index at least 35 kg/m(2)).

      Design:

        -  Participants will be screened with a medical history, physical examination, and blood
           and urine tests.

        -  Participants will spend the entire study (13 days) as inpatients at the National
           Institutes of Health Clinical Center.

        -  Participants will have the following tests and procedures:

        -  Body composition assessment (using low-level x-rays) to determine the percentage of fat
           tissue in the body.

        -  Oral glucose tolerance test (similar to that often used to diagnose diabetes).
           Individuals who are suspected to have diabetes will not be allowed to continue with the
           study.

        -  High salt infusion test, in which an infusion of saline (salt water) will be given for 2
           hours and participants will respond to questions about how hungry and thirsty they feel
           during the procedure.

        -  Water deprivation test, in which participants will go for 24 hours without water or food
           and respond to questions about how hungry and thirsty they feel.

        -  24-hour stay in a metabolic chamber to determine how many calories participants burn in
           a day.

        -  A series of questionnaires about participants' eating habits, feelings about food, and
           personal feelings, as well as computer-based tests involving the performance of various
           tasks.

        -  Measurement of free-living energy using doubly-labeled water, in which participants will
           drink a sample of water with extra-heavy atoms of hydrogen and oxygen to evaluate the
           amount of water in the body.

        -  24-hour urine collection.

        -  Frequent blood samples, urine collection, and fat tissue biopsies during the various
           study procedures.

        -  After the end of the 13-day study, participants will return after 1 week for a final
           urine collection.
    

Detailed description: 
      The percentage of people with overweight / obesity in the United States has reached very high
      levels, with 65% of adults over the age of 20 being overweight. Recently, there have been a
      number of advances in our understanding of the underlying causes of obesity, including
      greater understanding of both the effects of the environment and effects that are hereditary
      (i.e., genetic).

      One area in which obese versus lean individuals may be different is how their bodies handle
      water balance and thirst. Studies done in animals suggest that individuals with greater body
      fat may tolerate periods without water better than lean animals. Thus, at least in animals,
      others have found a link between ability to tolerate periods without water and increased body
      weight.

      We are studying whether the ability to tolerate periods without water and ability to feel
      thirst might differ in lean versus obese individuals. To do so, we will ask lean and obese
      individuals to undergo tests that include a period of approximately 24 hours without drinking
      any water, and on a separate day a shorter period of an intravenous high salt solution
      infusion. We will be looking at how the ability to withstand thirst (dehydration), subsequent
      water intake (rehydration), changes in hormone levels during these periods, and behavioral
      and physiological responses to thirst and rehydration differ in lean versus obese
      individuals. We hope that the data gathered from this study will give us more information
      about important differences in how water balance is regulated in lean versus obese
      individuals. Understanding these questions may provide new insights into differences between
      lean and obese individuals.
    

Intervention name(s): Hypertonic saline infusion; Water deprivation
Intervention type(s): Other; Other
Intervention description(s): Three percent saline (0.1ml/kg of the lean mass/min) will be infused for 120 minutes.; 24 hour water deprivation
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Hypertonic Saline Infusion; Water Deprivation; Thirst; Water/Electrolytes Homeostasis; Obesity