Water Deprivation Protocol

Study 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. Objectives: Primary Objective: to determine if obese versus lean individuals differ in their response (as measured by objective measurement of water intake) to water deprivation and hyperosmolality (dehydration). Secondary Objective: to determine if during these challenges there are differences in hormonal responses to dehydration and subsequent rehydration, and how these changes are related to adiposity and adipose tissue metabolism.