| Weight loss is associated with bone loss and increased fracture risk, and bone loss may be greater in non-obese compared to obese individuals. Ca supplementation can prevent bone loss in obese women, yet Ca supplementation in overweight women has not been studied. In this dissertation, we examined different levels of Ca intake for their ability to minimize bone loss during weight loss in overweight women. In addition, because the severity of weight loss may influence the amount of bone that is lost, the response of intestinal Ca absorption to massive weight loss was investigated. We hypothesized that Ca intake would influence Ca metabolism and the rate of bone turnover and loss after 6 months of weight loss. Bone mass was measured by dual-energy x-ray absorptiometry, and Ca absorption (using a dual stable Ca isotope method), hormones, and markers of bone turnover were measured. We showed that weight loss resulted in a decrease in bone mass at several sites in postmenopausal women on normal Ca intake (∼1 g/d), but bone loss was attenuated in the group consuming 1.7 g/d. The higher Ca intake seemed to offset some of the detrimental effects of higher cortisol, lower estrogen, and reduced weight bearing on bone. In overweight premenopausal women, we showed that weight loss did not induce a decrease in BMD with either normal (∼1 g/d) or high (1.8 g/d) Ca intake. We also showed that despite a decrease in TFCA with Ca supplementation, greater amounts of Ca absorbed were absorbed in the group with high Ca intake. Severe weight loss induced by Roux-en-Y gastric bypass surgery resulted in a dramatic decrease in Ca absorption, but because higher Ca intake in this group didn't suppress TFCA, it resulted in greater amounts of absorbed Ca. These results suggest that the regulation of Ca metabolism and bone loss during caloric restriction is primarily regulated by a decrease in estrogen in postmenopausal women, and that bone loss does not occur in premenopausal women who consume adequate or high Ca intake. Overall, it was found that Ca recommendations are inadequate during caloric restriction in postmenopausal, but are sufficient for premenopausal women. |
