Miller, Sibyl Nichole 1980- (2009-05). Paradoxical effects of variant nutrients' restriction on bone health during a long-term aerobic exercise paradigm in female rats. Master's Thesis.
Thesis
We sought to elucidate the individual nutrient restriction responsible for the greatest negative effects during exercise and food restriction. Sixty virgin, Sprague-Dawley female rats aged 4 months were acclimated to AIN-93M diet for 8 weeks prior to the 12-week protocol. Rats were randomly assigned to 6 groups (n=10/group). The control groups ate AIN-93M ad libitum and either exercised (EX-CON) or remained sedentary (SED-CON). The protein- (EX-PRO), calcium- (EX-CAL), and energy-restriction (EX-ENE) groups were fed custom diets providing 40% less protein, calcium, or energy, respectively; the global food-restriction group (EX-ALL) was fed 40% less of all nutrients. Exercise for all groups except SED-CON consisted of treadmill training 3 times/week for 45 minutes/session. Peripheral quantitative tomography (pQCT) scans were performed at baseline and at weeks 4 and 12 on the proximal tibia metaphysis (PTM) and midshaft tibia. After euthanization uterine weights were recorded; excised femurs were scanned at the neck and midshaft prior to three-point bending and femoral neck compression tests for mechanical properties. Significant reductions in body weight from baseline were observed concurrent with decrements in volumetric BMD (vBMD) in cancellous vBMD in EX-ALL and EX-ENE versus control groups at the PTM. Uterine weights were significantly lower in both groups compared to controls suggesting reduced circulating estrogen levels with global food and energy restriction. SED-CON and EX-PRO cortical vBMC significantly lower for EX-CAL and EX-ENE when compared to EX-CON and EX-PRO; and EX-PRO ultimate load (reflecting resistance to fracture) was larger then EX-CON. At the femoral neck EX-ENE total area was maintained, but the marrow area was larger versus EX-CON, suggesting endocortical resorption. Energy restriction manifested its effects in both metaphyseal and diaphyseal bone, but global food restriction only exerted its effects on metaphyseal bone; therefore energy restriction proved more detrimental to bone health then global food restriction. Unlike other studies, our treatment included an aerobic exercise protocol which may have mitigated some of the deleterious effects usually seen during food restriction. Unexpectedly, protein restriction appears to improve many bone outcomes compared to the exercising control group.
