• Calcium absorption and kinetics [ Time Frame: Baseline, day 5 and week 6 ] [ Designated as safety issue: No ]
  

• Serum Parathyroid hormone [ Time Frame: baseline and weekly ] [ Designated as safety issue: No ]
  
• Markers of bone turnover [ Time Frame: baseline and weekly ] [ Designated as safety issue: No ]
  

The protocol is composed of a 9.5-week study, consisting of a 3-week adjustment period followed by a 6.5-week experimental period. During the adjustment period, subjects consume a well-balanced lead-in diet designed to stabilize baseline Ca homeostasis. In the subsequent experimental period, subjects will consume the experimental diet containing 0.7 g protein/kg, 800-1200 mg phosphorus, 800 mg calcium and 2300 mg sodium. During days -6 to -1 of the adjustment diet, 5-10 and days 40-45 of the experimental period, we will measure Ca absorption and kinetics. Weekly assessments of Ca homeostasis will be done using our standard measures of calcitropic hormones, markers of bone turnover, and urine and serum minerals.

Inclusion Criteria:

• Healthy Asian or Caucasian women between the ages of 20-40 years.

Exclusion Criteria:

• Diseases or medical conditions: gastrointestinal diseases, osteoporosis, diabetes, hypertension, liver disease, thyroid disorders, kidney disease, kidney stones, cancer, heart disease, eating disorders, obesity, hypogonadism , amenorrhea, oligomenorrhea, abnormal serum FSH or estradiol levels, birth control medication, or other hormone-altering medications, pregnancy.
• Lifestyle: smoking, excessive exercise (although moderate exercise is allowed), prescription medications known to influence vitamin D or calcium metabolism or gastric acid, excessive body weight change during the past 6 months, food allergies, unusual eating habits, or medically prescribed diets.
• Also excluded are prisoners and individuals who are cognitively impaired.