Background Energy balance (EB) and its relation to nutrition status throughout the perioperative period of liver transplantation (LTx) patients has been poorly reported in the literature, and this is the primary objective of the current study. Methods A prospective observational study was conducted with patients undergoing LTx, who were assessed before and after the operation. Resting energy expenditure, total energy expenditure (TEE), dietary intake, and EB were evaluated, as well as anthropometry, handgrip strength, and standard phase angle (SPA). The presence of complications after the operation, length of intensive care unit and hospital stay, and death were registered. A P‐value < 0.05 was considered statistically significant. Results The average age was 54.1 ± 11.5 years; 79.3% of the patients were male, and the mean model for end‐stage liver disease (MELD) score was 16.7 ± 4.6. Negative EB was seen in 71.4% and 77.8% of patients before and after LTx, respectively. Food intake further decreased after the operation, leading to a significantly more negative EB. The prevalence of malnutrition ranged from 17.2% to 57.7% pretransplantation and 30.8% to 86.4% postoperatively, according to the different methods used. Increased preoperative TEE (0.040) and age (0.039) were predictive factors for complications, and low SPA was a predictive factor of death (0.038). Conclusion Negative EB was prevalent, and this was associated with high rates of malnutrition. These data reinforce the importance of individual nutrition assessment, including dietary intake, to tailor early nutrition interventions.