The purpose of this study is to identify calcium metabolism characteristics in Mexican American adolescents. The investigators predict that calcium requirements to maximize bone health in this population will be lower than for white youth but higher than their current intakes.

Previously significant racial and sex differences in calcium retention and kinetics in adolescents has been found. Other minority groups have increased calcium absorption efficiency at low calcium intakes in contrast to white adolescents. Since Hispanics and specifically Mexican Americans will soon comprise an increasing proportion of our population. We propose to identify calcium metabolism characteristics in this group. We predict that calcium requirements to maximize bone health in this population will be lower than for white youth but higher than their current intakes.

Thus the specific aims of this project include:

• to establish calcium requirements
• to establish the relationship between calcium intake and calcium absorption
• to identify the major physiological parameters(kidney, intestine, bone) that contribute to calcium retention in Mexican-American adolescents

During this two-phase metabolic camp participants will consume either a higher calcium diet(1100-2300mg/d) or a lower calcium diet (600-1200mg/d) during the first 3-week phase and switch to the opposite regime during the second 3-week phase, with a 2-week washout period in between. Subjects will collect all excreta during both phases. Calcium absorption, height, weight, and bone density will evaluated throughout the 6-week period of the study.

Inclusion Criteria:

• Normal, healthy adolescents of Mexican American descent
• Mexican American boys age 13-15
• Mexican American girls age 12-14

Exclusion Criteria:

• Malabsorptive disorders
• Anemia
• Smoking
• History of medications known to affect calcium metabolism
• Body weight outside 85-120% of ideal body weight for height
• Regular consumption of illegal drugs
• Contraceptive use
• Pregnancy