ESTIMATION OF BODY-COMPOSITION CHANGES DURING WEIGHT CYCLING BY BIOELECTRICAL IMPEDANCE ANALYSIS IN RATS

The effects of body weight cycling (WC) in rats on body composition (B C) and feeding efficiency were studied. The usefulness of estimating B C by bioelectrical impedance analysis (BIA) was also examined. Female Sprague-Dawley rats were divided into high-fat ad libitum feeding, eit her noncycling or cycling, or restricted feeding (75% of control feed) cycling groups. Control rats were fed a regular laboratory ad libitum diet and did not cycle. All rats were killed at the end of week 61. A BIA unit was used at each stage of WC to obtain resistance and reacta nce readings. Final BC was determined by chemical analysis. On the bas is of the final chemical analysis and BIA measurements, an equation wa s established and applied to estimate BC at each stage of WC: fat-free mass (g) = 0.38 x body wt (g) + 13.8 X [length (cm)2/resistance] + 70 .9 (r = 0.95, P < 0.001). High-fat ad libitum feeding induced rapid bo dy weight and fat gains as well as an elevated feeding efficiency and an internal fat-to-subcutaneous fat ratio, regardless of whether the r ats cycled. This change in fat mass was clearly detected by the BIA. A lthough rats fed restricted diets had similar body weights as did cont rol rats, they had a significantly higher internal fat-to-subcutaneous fat ratio. Thus, not only the amount of food but also the composition of the diet is important for proper weight management. The BIA method is capable of detecting the body fat mass change during WC.