Background: - Researchers who study health and nutrition are interested in developing more accurate methods of determining what people eat from day to day and how it affects their general health. In particular, better methods are needed to determine if people are accurately remembering what they ate. One possible method involves the use of biomarkers, or indicators in urine, blood, saliva, fat, and hair, which are related to the intake of a particular food in a consistent way. One set of biomarkers in blood samples and hair may be used to determine the relative amount of meat, fish, and soda (corn/sugar cane) in a person s diet. However, more research is needed to study the effectiveness of using these biomarkers to accurately track dietary intake. Objectives: - To validate the use of biomarkers as representative of specific dietary intake patterns (meat/fish/soda). Eligibility: - Healthy, nondiabetic men between 18 and 65 years of age. Design: - This study involves an initial screening visit and a 12-13 week inpatient dietary study period. - Participants will be screened with a medical history and physical examination, as well as blood and urine samples and a glucose tolerance test to exclude individuals who have diabetes. - After 3 days of a standard weight-maintaining diet, participants will have a glucose tolerance test and a body fat scan; provide hair, blood, and fat tissue samples; and complete questionnaires and performance tests. - Participants will spend one day in a metabolic chamber to measure their energy expenditure and general metabolism. - Participants will then be randomized into one of eight carefully designed diets for 12 weeks. The diets will differ in the amount of meat, fish, and soda, including one diet where none of the three biomarker-related foods will be permitted. Blood samples will be collected throughout the study diet period. - At the end of the 12-week study diet period, participants will provide additional hair, blood, and fat tissue samples, and will have a second metabolism assessment in the metabolic chamber.

This study will investigate how to better predict why some individuals gain or lose weight more easily than others. It will examine whether the increase in the amount of energy a body burns in 24 hours with overeating or the decrease over 24 hours with fasting can help determine how easily someone gains or loses weight. Healthy people between 18 and 60 years of age who have a body mass index (BMI) between 18.5 kg/m(2) and 24 kg/m(2) (for overfeeding study) or a BMI greater than 27 kg/m(2) with a body weight less than 350 pounds (weight loss study) may be eligible for this study. The study requires a 10-week admission to the NIH Clinical Center (2-week baseline, 6-week overfeeding/weight loss, 2-week post-weight change). Participants undergo the following tests and procedures during the hospital admission: - Medical history, physical examination and laboratory studies - Questionnaires to assess eating behavior, food preferences, body composition, and activity level - Body composition assessment (height, weight, waist circumference, and fat mass and muscle content through DXA and MRI scans) - Oral glucose tolerance test - Meal test to measure the response of certain hormones to food - Activity monitors to determine activity level - Metabolic chamber study to measure calories burned over 24 hours and monitor body temperature - Free-living energy use study to measure calories burned under normal home conditions over 7 days - Fat and muscle biopsies - Dietary intervention: Measurements of food intake and energy loss over a 6-week overfeeding (1.5 times the subject s normal food intake) or weight loss (one-half the subject s normal food intake) program Followup procedures after the inpatient stay: - Height and weight measurements at 6 months (overfeeding study participants) and monthly for the first year, at 3-month intervals for the second year, and then yearly for 3 more years (weight loss study participants) - Yearly visits (2-night inpatient stay) for all participants for repeat meal test, DXA, oral glucose tolerance test, behavioral questionnaires and, in women who can become pregnant, pregnancy test

The prevalence of obesity in the United States has reached alarming proportions with 33% of adults over the age of 20 being overweight. Obesity is more than twice as prevalent, however, in the Pima Indians of Arizona. Although there have been a number of advances in our understanding of the genetics of obesity, the environmental influences on the genetic expression of obesity requires further investigation. In an effort to understand some of the influences on the high prevalence of obesity in the Pima Indians, the present study was designed to investigate eating behaviors and food preferences, most especially the preference for high fat foods, in sib-pairs of Pima Indians who have been previously genotyped in our genomic scan for loci linked to diabetes/obesity. Most specifically, we will utilize several questionnaires and methods of assessing eating behavior and the preference for high fat foods to create a food intake phenotype. In addition, we will study Caucasians so that comparisons can be made between these two groups. We will make these evaluations by assessing eating behavior, food preferences including usual fat intake and preferences for high fat foods, body image perceptions, and energy expenditure. It is hoped that the data gathered from this study will elucidate some of the risk factors for the development of obesity among the Pima Indians.