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Objective: To assess bone mineral content (BMC) among obese adolescents who lose weight during a critical period for bone accretion.

Methods and Procedures: Whole body, lumbar spine, lower, and upper limb BMC were measured in 62 obese adolescents who completed an intensive 12-month weight loss trial. BMC was adjusted for height (z -scores) using data from a reference group of 66 adolescents (who were 18% overweight).

Results: At baseline, the BMC of the obese group was higher than the reference group. During the 12-month weight loss program, unadjusted BMC increased among the obese adolescents, despite successful weight loss. After adjustment for height, whole body BMC did not change significantly from baseline to 12 months (mean ± s.d.: 1.08 ± 0.67 to 1.06 ± 0.67, P = 0.7). Region-specific BMC-for-height however decreased for the lower (1.07 ± 0.57 to 0.95 ± 0.59, P < 0.001) and upper (1.29 ± 0.56 to 1.18 ± 0.57, P = 0.01) limbs, but lumbar spine BMC-for-height increased (0.14 ± 1.06 to 0.40 ± 0.94, P < 0.001). These changes were largely and independently explained by changes in lean and fat mass.

Discussion: This study confirms that obese adolescents have high BMC for height and suggests that, unlike adults, their BMC continues to increase during weight loss and remains higher than the BMC of a reference group. After adjustment for growth-related changes, lower and upper limb BMC appears to decrease, while lumbar spine BMC appears to increase. These results suggest that to optimize the health benefits of weight loss among obese adolescents, their bone health should be better understood and addressed.