Effects of Diet Changes on Metabolism

This study, conducted at the NIH Clinical Research Unit at the Phoenix Indian Medical Center, will examine how the body s metabolism (energy expenditure) changes when people overeat and when they fast and how different diets (e.g., high-protein or high-fat) affect metabolism. The results may provide information about whether there are mechanisms that make some people more resistant than others to gaining weight when they eat more. Non-smoking healthy subjects between 18 and 55 years of age who weigh no more than 350 pounds may be eligible for this study. Participants undergo the following procedures: * Pregnancy test for women of childbearing age. * Oral glucose tolerance test. For this test, an I.V. line (needle attached to a plastic tube) is inserted into a vein to allow several blood draws without repeated needle sticks. After the first blood sample is drawn, the subject drinks a cola-flavored sugar solution. Five additional blood samples are then drawn over 3 hours. * Blood test for DNA (genetic) studies related to obesity, diabetes and related medical problems. * DEXA scan. This test measures body fat. The subject lies on a table while a very small dose of X-rays is passed through the body. * Respiratory chamber. This test measures how many calories the body burns a day and assesses energy balance between intake and expenditure. Subjects stay in a room with two windows, equipped with a sink, toilet, television and DVD player, desk, chair, telephone and bed for 24 hours. The test is repeated five times during the first 18-day admission and 3 times during the second 13-day admission. For the first two sessions, subjects are fed a diet equal to the amount of energy their body uses. For the next 6 stays they are fed double the amount of calories their body usually uses for 5 of the stays and fast (consume nothing but water and soda without caffeine or calories) during 1 stay. The overfeeding diets may be high or low in protein, normal in protein, or high in fat.