Hasina Ambia-Sobhan

Areal and Volumetric Bone Mineral Density and Geometry at Two Levels of Protein Intake During Caloric Restriction: A Randomized, Controlled Trial

Weight reduction induces bone loss by several factors, and the effect of higher protein (HP) intake during caloric restriction on bone mineral density (BMD) is not known. Previous study designs examining the longer‐term effects of HP diets have not controlled for total calcium intake between groups and have not examined the relationship between bone and endocrine changes. In this randomized, controlled study, we examined how BMD (areal and volumetric), turnover markers, and hormones [insulin‐like growth factor 1 (IGF‐1), IGF‐binding protein 3 (IGFBP‐3), 25‐hydroxyvitamin D, parathyroid hormone (PTH), and estradiol] respond to caloric restriction during a 1‐year trial using two levels of protein intake. Forty‐seven postmenopausal women (58.0 ± 4.4 years; body mass index of 32.1 ± 4.6 kg/m2) completed the 1‐year weight‐loss trial and were on a higher (HP, 24%, n = 26) or normal protein (NP, 18%, n = 21) and fat intake (28%) with controlled calcium intake of 1.2 g/d. After 1 year, subjects lost 7.0% ± 4.5% of body weight, and protein intake was 86 and 60 g/d in the HP and NP groups, respectively. HP compared with NP diet attenuated loss of BMD at the ultradistal radius, lumbar spine, and total hip and trabecular volumetric BMD and bone mineral content of the tibia. This is consistent with the higher final values of IGF‐1 and IGFBP‐3 and lower bone‐resorption marker (deoxypyridinoline) in the HP group than in the NP group (p < .05). These data show that a higher dietary protein during weight reduction increases serum IGF‐1 and attenuates total and trabecular bone loss at certain sites in postmenopausal women.

Effects of formalin fixation and collagen cross-linking on T2 and magnetization transfer in bovine nasal cartilage.

Endogenous collagen cross‐links influence cartilage biomechanical properties and resistance to degradation. Formalin fixation modifies collagen residues and forms new cross‐links in a dose‐dependent manner. We tested the hypothesis that magnetization transfer (MT) effects and T2 depend on collagen cross‐linking in cartilage. These parameters were measured in bovine nasal cartilage (BNC) prior to fixation, after 9 weeks of immersion in formalin solutions ranging in concentration from 0% to 10%, and after NaBH3CN reduction and washing. T2 decreased by 59.4% ± 1.1% upon fixation in 10% formalin, and was 32.2% ± 5.2% shorter than initial values after washing. The apparent MT rate increased 25.9% ± 3.7% and 52.8% ± 7.1% over baseline under these conditions. Biochemical assays showed no significant differences in water, proteoglycan, natural cross‐link, or collagen content between the 0% and 10% formalin‐treated samples, while amino acid analysis demonstrated losses in (hydroxy)lysine and tyrosine, and new peaks consistent with methylene cross‐links in fixed samples only. We conclude that formalin fixation of cartilage results in significant decreases in T2 and increases in MT parameters that persist after removal of unreacted formaldehyde. The collagen cross‐links thus created are associated with large changes in MT and T2, indicating that interpretation of T2 and MT values in terms of cartilage macromolecular content must be made with caution. Magn Reson Med 57:1000–1011, 2007. Published 2007 Wiley‐Liss, Inc.

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

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 (-91 +/- 34 g) than lean EnR rats(-61 +/- 14 g) (P < 0.02), [corrected] 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.

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

BackgroundAlthough 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.MethodsFemale 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.ResultsRats 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 RS2 had 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.ConclusionWeight cycling reduces bone mass. A diet high in RS2 can minimize loss of bone mass during weight cycling and may increase bone mass in the absence of weight cycling.

Blood lead levels and bone turnover with weight reduction in women

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.