4.6 Article

Energy restriction reduces fractional calcium absorption in mature obese and lean rats

Journal

JOURNAL OF NUTRITION
Volume 132, Issue 9, Pages 2660-2666

Publisher

AMER INST NUTRITION
DOI: 10.1093/jn/132.9.2660

Keywords

absorption; calcium; estrogen; rats; weight loss

Funding

  1. NIA NIH HHS [AG-12161, R01 AG012161] Funding Source: Medline

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Weight loss is associated with bone loss and the risk may be greater in lean than heavier individuals, but the mechanisms involved remain unclear. We hypothesized that energy restriction (EnR) would decrease true fractional Ca absorption (TFCA) and be mediated by Ca-regulating hormones, but differently in obese and lean rats. Rats were fed a high fat (47% energy) or low fat (16% energy) diet for 4 mo. At 6 mo of age, the resulting lean [284 +/- 28g (mean +/- (SD), n = 18)] and obese (319 +/- 34g, n = 20) groups (P < 0.005) were divided into controls (CTL, ad libitum) and energy-restricted (40% restriction) groups. At baseline, bone resorption (urinary crosslinks) was higher and bone formation (serum osteocalcin) was lower in obese than in lean rats, whereas Ca balance components and Ca-regulating hormones did not differ. EnR for 10 wk reduced body weight by 25 +/- 7% compared with a 6 +/- 6% gain in CTL rats (P < 0.001). For both lean and obese rats, TFCA (5-d measurement Ca-45 radioisotope) decreased from 30 +/- 9% to 24 +/- 9% with EnR, compared with 25 +/- 10% to 29 +/- 11% in controls (P < 0.05). Weight loss was directly correlated with the decrease in TFCA (r = 0.34, P < 0.05). Uterine weights indicated a reduced estrogenic activity in energy-restricted rats (P < 0.0001). In lean, but not obese rats, serum estradiol (E-2) correlated with weight loss (r = 0.52, P < 0.05), and tended to correlate with the decrease in TFCA (r = 0.48, P = 0.06). At the end of the study, serum 25-hydroxyvitamin-D was lower and urinary Ca was higher in lean than obese energy-restricted rats. Distinct endocrine profiles during weight loss in obese and lean rats suggest that the susceptibility of bone and Ca metabolism to EnR could differ depending on initial body weight.

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