Exercise, dietary obesity, and growth in the rat

Four regimens: high-fat diet, exercised (I); chow, exercised (II); high-fat sedentary (III); and chow, sedentary (IV) were initiated in 35-day-old male rats. Growth was exponential in I and II and exponential progressing to rectilinear in III and IV. The exponential model predicted the decreasing rank order in asymptotic weight to be: III, IV, I, II. Body composition data (9 components) showed rank order in masses of fat and the fat-free body mass compartment (FFBM) to be the same as for asymptotic live weight. The rectilinear growth mode probably reflected fat accretion. High-fat diet increased and treadmill exercise decreased FFBM, the latter being reversible. These effects depended on regimen initiations by the 5-7th wk of age. During growth, masses of H2O, muscle, and skin increased as functions of body size; bone as a function of age; and heart, liver, gut, testevity, and diet. Growth in body size was expressed more precisely with FFBM, instead of live weight, as the index of size.