Critically ill patients, such as those with trauma or sepsis, experience high rates of malnutrition (up to 75%). Malnutrition worsens outcomes by increasing infection rates, hospital stays, mortality, and healthcare costs. Adequate nutrition is therefore crucial in the ICU. To ensure appropriate nutrition, accurate determination of total energy expenditure (TEE) is essential. In practice, predictive equations are often used, but these can misestimate TEE in ICU patients due to complex metabolic changes. Indirect calorimetry is recommended but limited by technical constraints. Consequently, the doubly labeled water (DLW) method, though expensive, offers a precise and non-invasive way to measure TEE over time. This study applies the DLW method in ICU patients to improve energy assessment and guide personalized nutrition strategies that support recovery and outcomes.