The energy metabolism of pigs, which initially differed in energy reserve in the body and size of internal organs, was measured using the comparative slaughter method on 90 Polish Landrace gilts kept individually and grown from 15 to 70 kg. During a restriction period from 15 to 25 kg, the pigs of group P consumed 40% less protein daily, while the pigs of group E 40% less feed as compared with the C pigs (control). During subsequent realimentation from 25 to 70 kg, all of the pigs were fed ad libitum (A), or at two restricted feeding levels: 85 (R85) or 60% (R60) of ad libitum intake, diets with low (12.4 MJ ME - L) or high (13.2 MJ ME - H) energy density. Thus, pigs were fed at five feeding levels: A_H, A_L, R_85H, R_85L, R_60H. The animals were slaughtered successively at 15 (n=4), 25 (n=12, four from the C, P and E groups) and 70 kg body weight (n=74). After slaughter, the protein and fat content in the body was estimated. Energy metabolism was measured according to a two-step model as recommended by ARC (1981), using the following equations: (1) MEI = ME_m + (1/k_g) × RE; (2) (ME - ME_m) = (1/k_p) × ∆P + (1/k_f) × ∆F. During the restriction period the maintenance requirement (ME_m) amounted to 647 kJ/kg^0.75 , utilization of ME energy for growth, 62% (k_g = 0.62), and coefficients k_p and k_f, 0.48 and 0.71, respectively. During realimentation the maintenance requirement (ME_m) amounted on average to 591 kJ/kg^0.75. Utilization of ME energy for growth came to 56 % (k_g = 0.56), and for protein and fat, 36 (k_p = 0.36) and 74 % (k_f = 0.74), respectively. Younger animals utilized ME energy for growth more effciently than older ones due to better utilization of ME energy for protein deposition.