Differential effects of rapid and slow body mass reduction on body composition during an equivalent weight loss in rats

SummaryIt is unclear whether the rate of body mass (BM) reduction affects the body composition with an equivalent BM reduction and whether this is influenced by the intensity of BM reduction. To elucidate this, two experiments (Exp.) were conducted. In Exp. 1, the rats fasted for 3 days to decrease BM rapidly (R3); energy was restricted at 85% of their estimated basal metabolic rate to decrease BM slowly, until it reached the same BM as R3 (S20). In Exp. 2, the rats fasted for 7 days (R7); received a restricted diet as in Exp. 1 (S50). The BM decreased 11% in R3 and S20 showed a BM equivalent to R3 on Day 20. In Exp. 2, the BM decreased 18% in R7 and S50 reached the BM of R7 on Day 50. The mass and water and protein in the skeletal muscle and adipose tissue mass did not differ between the groups in both experiments. In contrast, the stomach mass was 12.9% lower in R3 than S20 (P < 0.05) and the liver mass was 9.9% lower in R3 (P = 0.078). In Exp. 2, the stomach and liver masses were 13.2% and 18.2% lower in R7 than S50 (P < 0.05), respectively. The differences in the rate of BM reduction were seen in splanchnic tissues than in skeletal muscles and adipose tissues regardless of BM intensity. The larger BM reduction appeared to be related to a greater difference in the liver mass between the rapid and slow BM reduction.