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. The 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 control 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 and R40R groups). Eight rats from the control group were killed at the beginning. Eight rats each from the control, R60 and R40 groups were killed at week 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, indicating the weight reduction rate for the R40 group was twice that of the R60 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 density, 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 weight, 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 R40 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 rate. Regardless of the weight reduction rate, bone density, breaking strength, ash weight, and Ca content could not recover along with body weight regain. (C) 2000 Elsevier Science Inc.