Nutritional insults early in life, such as during the suckling phase, are associated with phenotypic alterations and promote adverse permanent effects that impair the capacity to maintain energy balance in adulthood. This study aimed to evaluate the long-term effects of a low-protein (LP) diet during lactation on the metabolism and antioxidant systems of adult female rat offspring. Dams were fed a low-protein diet (4% protein) during the first two weeks of lactation or a normal-protein (NP) diet (20% protein) during the entire lactation period. The female offspring received a standard diet throughout the experiment. At 90 days of age, female LP offspring exhibited decreased body weight, feeding efficiency, and fat pad stores. The adult LP female offspring displayed brown adipose tissue hyperplasia without alterations in glucose homeostasis. The LP diet decreased liver triglyceride content and improved the antioxidant system compared to the NP group. The LP diet during the suckling phase promotes a lean phenotype and improves the hepatocyte antioxidant system in adult female offspring. Thus, the LP diet may play an important role in homeostasis and the prevention of metabolic damage.