Bone composition and strength of female rats subjected to different rates of weight reduction

Seventy-two rats (7 months old) were assigned into three dietary groups. Th e control group was fed ad lib AIN-76 diet, the R60 group a diet providing 60%, and the R40 group a diet providing 40% of the energy consumed by the c ontrol group. During the initial 4 weeks before switching to the R40 diet, the R40 group was fed the same as the control. At week 8, 8 rats each from R60 and R40 groups were given energy supplement plus the assigned diets for 4 weeks to regain their lost body weight before killed at week 12 (R60R an d R40R groups). Eight rats from the control group were killed at the beginn ing. Eight rats each from the control, R60 and R40 groups were killed at we ek 8 and 12. Body weight of R60 group decreased within 8 weeks and that of R40 group did within 4 weeks both by 24% of their initial body weight, indi cating the weight reduction rate for the R40 group was twice that of the R6 0 group. The R60 group had lower bone density, breaking strength, and bone Ca content (all at P < 0.05) than the R40 group at week 8 and 12. Bone dens ity, breaking strength, ash weight, and Ca content became lower from week 8 to week 12 for R60 and R40 groups. At week 12, fat-free bone weight, ash w eight, and Ca content were higher for the control than for the other groups (P < 0.05), but they were not different between R60 and R60R or between R4 0 and R40R. In conclusion, body weight reduction at a slower rate resulted in more bone loss than a similar extent of weight reduction at a faster rat e. Regardless of the weight reduction rate, bone density, breaking strength , ash weight, and Ca content could not recover along with body weight regai n. (C) 2000 Elsevier Science Inc.