Exercise, dietary obesity, and growth in the rat

Experiments were conducted on weanling male rats 35 days old and weighing about 100 g to determine how endurance-type exercise and high-fat diet administered during growth influence body mass and composition. The animals were divided into four weight-matched groups of 25 animals each: group I - high-fat diet, exercised; group II - chow, exercised; group III - high-fat diet, sedentary; and group IV - chow, sedentary. During growth, masses of water, muscle and skin increased as functions of body size; bone as a function of age; and heart, liver, gut, testes, and CNS were affected by combinations of size, age, activity, and diet. Major conclusions are that growth in body size is expressed more precisely with fat-free body mass (FFBM), that late rectilinear growth is probably attributable to fat accretion, and that the observed influences on FFBM of exercise and high-fat diet are obtained only if the regimen is started at or before age 5-7 weeks.