title: Weight loss and calcium intake influence calcium absorption in overweight postmenopausal women.
abstract: BACKGROUND
  Weight loss (WL) reduces bone mass and increases fracture risk. Mechanisms regulating calcium metabolism during WL are unclear.
  
  
  OBJECTIVE
  The objective was to assess the effect of 6 wk of WL at 2 different amounts of calcium intake [normal (NlCa): 1 g/d; high (HiCa): 1.8 g/d] on true fractional calcium absorption (TFCA), bone turnover, and bone-regulating hormones in overweight postmenopausal women.
  
  
  METHODS
  Seventy-three women (body mass index, 26.9 +/- 1.9 kg/m(2)) were recruited either to consume a moderately energy-restricted diet (WL group) or to maintain their body weight [weight-maintenance (WM) group] and were randomly assigned to either the HiCa or the NlCa group in a double-blind manner. Subjects underwent weekly diet counseling, and measurements were taken at baseline and after 6 wk.
  
  
  RESULTS
  Fifty-seven women completed the study and had a baseline TFCA of 24.9 +/- 7.4%. Energy restriction significantly decreased the total calcium absorbed (P < 0.05) in the WL group (n = 32) compared with the WM group (n = 25; analysis of covariance). Regression analysis showed that a greater rate of weight loss suppressed TFCA and the total calcium absorbed (P < 0.05) in the HiCa group. The women in the NlCa WL group absorbed inadequate amounts of calcium (195 +/- 49 mg/d), whereas the women in the HiCa WL group absorbed adequate amounts (348 +/- 118 mg/d). Parathyroid hormone explained 22% of the variance in calcium absorbed in the NlCa group only.
  
  
  CONCLUSIONS
  We suggest that WL is associated with elevated calcium requirements that, if not met, could activate the calcium-parathyroid hormone axis to absorb more calcium. Normal intakes of calcium during energy restriction result in inadequate total calcium absorption and could ultimately compromise calcium balance and bone mass.
authors.affiliation: Department of Nutritional Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
authors.forename: Mariana
authors.initials: M
authors.lastname: Cifuentes
authors.forename: Claudia S
authors.initials: CS
authors.lastname: Riedt
authors.forename: Robert E
authors.initials: RE
authors.lastname: Brolin
authors.forename: M Paul
authors.initials: MP
authors.lastname: Field
authors.forename: Robert M
authors.initials: RM
authors.lastname: Sherrell
authors.forename: Sue A
authors.initials: SA
authors.lastname: Shapses
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D015519:Bone Density; D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000493:pharmacokinetics; D004038:Diet, Reducing / Q000009:adverse effects; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D008875:Middle Aged; D009765:Obesity / Q000178:diet therapy / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology; D017698:Postmenopause / Q000378:metabolism*; D012044:Regression Analysis; D012621:Seasons; D015431:Weight Loss / Q000502:physiology*
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D002118:Calcium