Bone mineral density and content during weight cycling in female rats: effects of dietary amylase-resistant starch

<p>Abstract</p> <p>Background</p> <p>Although there is considerable evidence for a loss of bone mass with weight loss, the few human studies on the relationship between weight cycling and bone mass or density have differing results. Further, very few studies assessed the role of dietary composition on bone mass during weight cycling. The primary objective of this study was to determine if a diet high in amylase-resistant starch (RS₂), which has been shown to increase absorption and balance of dietary minerals, can prevent or reduce loss of bone mass during weight cycling.</p> <p>Methods</p> <p>Female Sprague-Dawley (SD) rats (n = 84, age = 20 weeks) were randomly assigned to one of 6 treatment groups with 14 rats per group using a 2 × 3 experimental design with 2 diets and 3 weight cycling protocols. Rats were fed calcium-deficient diets without RS₂(controls) or diets high in RS₂(18% by weight) throughout the 21-week study. The weight cycling protocols were weight maintenance/gain with no weight cycling, 1 round of weight cycling, or 2 rounds of weight cycling. After the rats were euthanized bone mineral density (BMD) and bone mineral content (BMC) of femur were measured by dual energy X-ray absorptiometry, and concentrations of calcium, copper, iron, magnesium, manganese, and zinc in femur and lumbar vertebrae were determined by atomic absorption spectrophotometry.</p> <p>Results</p> <p>Rats undergoing weight cycling had lower femur BMC (p < 0.05) and marginally lower BMD (p = 0.09) than rats not undergoing weight cycling. In comparison to controls, rats fed RS₂had higher femur BMD (p < 0.01) and BMC (p < 0.05), as well as higher values for BMD and BMC measured at the distal end (p < 0.001 and p < 0.01) and femoral neck (p < 0.01 and p < 0.05). Consistent with these findings, RS₂-fed rats also had higher femur calcium (p < 0.05) and magnesium (p < 0.0001) concentrations. They also had higher lumbar vertebrae calcium (p < 0.05) and magnesium (p < 0.05) concentrations.</p> <p>Conclusion</p> <p>Weight cycling reduces bone mass. A diet high in RS₂can minimize loss of bone mass during weight cycling and may increase bone mass in the absence of weight cycling.</p

Blood lead levels increase, but remain in normal range with severe weight reduction.

High bone turnover states are known to raise blood lead levels (BPb). Caloric restriction will increase bone turnover, yet it remains unknown if weight reduction increases BPb due to mobilization of skeletal stores. We measured whole blood Pb levels (²⁰⁶Pb) by inductively coupled plasma mass spectrometry in 73 women (age 24–75 years; BMI 23– 61 kg/m²) before and after 6 months of severe weight loss (S-WL), moderate weight loss (M-WL), or weight maintenance (WM). Baseline BPb levels were relatively low at 0.2–6.0 μg/dl, and directly associated with age (r=0.49, P<0.0001). After severe WL (-37.4±9.3 kg, n=17), BPb increased by 2.1±3.9 μg/dl (P<0.05), resulting in BPb levels of 1.3–12.5 μg/dl. M-WL (-5.6±2.7 kg, n=39) and WM (0.3±1.3 kg, n=17) did not result in an increase in BPb levels (0.5±3.2 and 0.0±0.7 μg/dl, M-WL and WM, respectively). BPb levels increased more with greater WL (r=0.24, P<0.05). Bone turnover markers increased only with severe WL and were directly correlated with WL. At baseline, higher calcium intake was associated with lower BPb (r=-0.273, P<0.02), however, this association was no longer present after 6 months. Severe weight reduction in obese women increases skeletal bone mobilization and BPb, but values remain well below levels defined as Pb overexposure.This research was supported by the NIEHS sponsored UMDNJ Center for Environmental Exposures and Disease, Grant number: NIEHS P30ES005022, in part by NIH-AG12161, and a Busch Biomedical Award to SA Shapses.National Institutes of Health: AG12161, to S.A. ShapsesCharles & Johanna Busch Biomedical Grant, to S.A. ShapsesThe published version of this paper is available at: http://www.nature.com/je

Energy Restriction Is Associated with Lower Bone Mineral Density of the Tibia and Femur in Lean but Not Obese Female Rats1–3

Energy restriction decreases bone mineral density (BMD), and epidemiological studies suggest that the risk of weight loss-induced bone loss is greater in lean than in heavier individuals. Our goal in this study was to determine how bone density and geometry respond to energy restriction in mature obese rats compared with lean rats. At 6 mo of age, 36 diet-induced obese and lean female Sprague-Dawley rats were allocated to control (CTL; ad libitum; n = 18) and energy-restricted (EnR; 40% restriction; n = 18) diets. After 10 wk of dietary intervention, obese EnR rats lost more weight (−61 ± 14 g) than lean EnR rats (−91 ± 34 g) (P < 0.02), whereas body weight did not change significantly in the 2 CTL groups (14 ± 23 g). Only the lean EnR (and not obese EnR) rats showed lower BMD compared with CTL rats at the tibia, distal, and proximal femur and femoral neck, and trabecular bone volume (P < 0.05). Serum estradiol declined in lean EnR rats compared with baseline (P < 0.05) but not in the obese EnR rats. In addition, the final serum 25-hydroxyvitamin D (25OHD) concentration was higher (P < 0.05) in obese than in lean EnR rats. Serum parathyroid hormone decreased (P < 0.05) from baseline to final in lean and obese CTL, but not EnR rats. These data support the hypothesis that energy restriction in lean rats compared with obese rats is more detrimental to bone, and it is possible that the greater decline in estrogen and lower levels of 25OHD contribute to this effect