The objective of this study was to evaluate the effect of feed restriction on protein metabolism of 84 Saanen goats (26 intact males, 27 castrated males and 31 females) with initial BW of 30,3 ± 0,87 kg. At the beginning of the experiment 8 intact males, 9 castrated males and 13 females were slaughtered with 30 kg of BW to estimate their initial body composition. The remaining 18 goats of each sex were assigned to 3 levels of feed restriction (ad libitum, 25% and 50% of feed restriction), with 6 goats per sex-feeding level (3 × 3 factorial). Animal sets (1 goat per sex-feeding level) were slaughtered when BW of ad libitum goats was 45 kg. Blood samples were collected every 14 d, in a total of 7 blood collections (98 d of experimental period). In these samples we evaluated total protein, albumin, urea, creatinine, triiodothyronine (T3) and IGF-1. Data were analyzed using Proc Mixed of SAS. Intact males presented lower body protein retention (kg) regardless the level of feed restriction (P = 0.020). Intact males fed ad libitum and with 50% of feed restriction had greater serum levels of creatinine in the blood (0.88 mg/dL and 1.28 mg/dL respectively; P = 0.014). Females fed ad libitum had lower urea levels (42.08 ± 1.83 mg/dL) than intact (51.1 ± 1.83 mg/dL) and castrated males (48.2 ± 1.81 mg/dL) however, when subjected feed restriction (25% and 50%), females increased serum levels of urea, whereas males had an opposite behavior. The feed restriction and sex did not affect serum albumin and total protein levels (P > 0.05). Intact males fed ad libitum and 25% feed restriction showed greater plasma levels of IGF-1 than females and castrated males (P = 0.018), but when fed 50% restriction, the IGF-1 concentration were similar between all sexes (85.0 ± 9.89 ng/mL). Plasma levels of T3 were similar in females and castrated males (1.57 ng/mL) and greater than in intact males (1.43 ng/mL; P = 0.001). The levels of IGF-1 and T3 in the blood showed a linear decrease with the increase of feed restriction (P < 0.0001). The feed restriction changed the protein metabolism in females and males. Pubertal males were not able to keep protein synthesis during feed restriction.