Investigation of Differences in Energy Metabolism and Nutrient Absorption Between Lean and Obese Individuals

Detailed Summary

This study will examine whether there are differences in energy (calories) losses in stool and urine between lean and obese people. People gain weight when the amount of calories in the food they eat is greater than the amount of calories their body uses to support its functions and activities. The balance between caloric intake and expenditure may be affected by the amount of calories from food that is not absorbed but is lost in stool and urine. This study will examine whether differences in food absorption are related to obesity. Healthy normal volunteers between 18 and 45 years of age with a body mass index (BMI) of 18-25 kg/m2 or less than 35 kg/m2 may be eligible for this 15-day study. Participants are admitted to the Clinical Research Unit at the Phoenix Indian Medical Center for the study. Participants undergo the following tests and procedures: * Experimental diets with dye marker: Subjects are fed a 2400-calorie diet and a 3400-calorie diet for 3 days each. On the first of the day of each diet, a blue dye marker is added to the breakfast meal. A red marker is added to the breakfast meal of the first day after the diet period. Urine is collected beginning after breakfast on the first day of the diet and until before breakfast on the last day of the diet. Stool samples are collected during the entire diet period, and until the appearance of the red dye in the stool. * 24-hour metabolic rate in the respiratory chamber: After the first diet period, subjects spend 24 hours in a respiratory chamber to measure the number of calories the body burns a day and to assess the energy balance between intake and expenditure. * Stool sample: Stool samples are collected on days 1 and 2 of the study to look for parasites or internal bleeding that may affect nutrient absorption. * DXA scanning: This scan uses a low dose of X-rays to measure body fat. * Oral glucose tolerance test: For this test for diabetes, an I.V. line (needle attached to a small plastic tube) is inserted into an arm vein. The subject drinks a sugar solution. Small blood samples are drawn from the I.V. before the subject drinks the solution and at five intervals during the 3 (Omega)-hour test period. * Fasting blood tests: On the first day of each diet and on the day after each diet is completed a blood sample is drawn before breakfast to measure hormones that may affect the ability to absorb food. At the end of the study, some participants may be asked to repeat the experimental diets and stool and urine collections. ...

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