Recent randomized controlled trials (RCTs) indicate that early full nutritional support in critically ill patients does not provide benefits and may cause harm due to anabolic resistance, suppression of cellular repair processes, and worsening of hyperglycemia and insulin needs. Early high amino acid doses also proved harmful in patients with organ dysfunction. Most studies focused on nutritional interventions initiated within the first days after ICU admission, but few examined those beyond the first week. This lack of evidence means there is no clear guidance on when and how to initiate and advance nutrition. Prolonged underfeeding may be harmful as there is no validated method to determine readiness for medical nutrition therapy, and micronutrient status is difficult to assess due to inflammation-induced redistribution. High doses of individual micronutrients have not been shown to be beneficial. Current evidence highlights which nutritional strategies to avoid, but the ideal regimen for individual patients remains unclear. The EPaNIC RCT showed that early parenteral nutrition prolonged ICU stay, increased infections, and impaired recovery. Similar results were found in the PEPaNIC RCT in children. The CALORIES and NUTRIREA-2 RCTs found no difference between enteral and parenteral nutrition with similar energy doses. The NUTRIREA-3 RCT found harm from early high-dose nutrition, with prolonged ICU stay and increased complications. These RCTs suggest dose-dependent harm from early medical nutrition therapy, regardless of the feeding route or perceived nutritional risk. Evidence has influenced clinical practice and guidelines, shifting toward less aggressive nutrition in the acute phase. European guidelines now recommend low-dose enteral nutrition within 48 hours of ICU admission, while American guidelines suggest either enteral or parenteral nutrition in the first 7–10 days. However, the optimal duration of the acute phase remains unclear, with differences between guidelines on the allowed time for below-target feeding. Micronutrient deficiencies are common in critically ill patients due to rapid depletion and increased utilization. Refeeding syndrome, a potentially life-threatening condition, can occur when micronutrient stores are low. Current guidelines recommend maintenance doses of micronutrients, but there is no validated standard for diagnosing refeeding syndrome. High pharmacological doses of individual micronutrients are not recommended as they have not been shown to be beneficial. Mechanisms explaining the lack of benefit from early high-dose nutrition include anabolic resistance, suppression of autophagy and ketogenesis, and increased stress hyperglycemia. Early full feeding may also lead to overfeeding and increased insulin needs. The time point when anabolic resistance switches into feeding responsiveness is unclear, making personalized nutrition challenging. Future research should focus on interventions beyond the acute phase and explore the role of indirect calorimetry in guiding energy dosing. Studies should also investigate the impact of optimizing nutritional intake in the post-acute phase on recovery and exercise. Additionally, the role of intermittent fasting/feeding strategies, ketogenic diets, and ketone supplementationRecent randomized controlled trials (RCTs) indicate that early full nutritional support in critically ill patients does not provide benefits and may cause harm due to anabolic resistance, suppression of cellular repair processes, and worsening of hyperglycemia and insulin needs. Early high amino acid doses also proved harmful in patients with organ dysfunction. Most studies focused on nutritional interventions initiated within the first days after ICU admission, but few examined those beyond the first week. This lack of evidence means there is no clear guidance on when and how to initiate and advance nutrition. Prolonged underfeeding may be harmful as there is no validated method to determine readiness for medical nutrition therapy, and micronutrient status is difficult to assess due to inflammation-induced redistribution. High doses of individual micronutrients have not been shown to be beneficial. Current evidence highlights which nutritional strategies to avoid, but the ideal regimen for individual patients remains unclear. The EPaNIC RCT showed that early parenteral nutrition prolonged ICU stay, increased infections, and impaired recovery. Similar results were found in the PEPaNIC RCT in children. The CALORIES and NUTRIREA-2 RCTs found no difference between enteral and parenteral nutrition with similar energy doses. The NUTRIREA-3 RCT found harm from early high-dose nutrition, with prolonged ICU stay and increased complications. These RCTs suggest dose-dependent harm from early medical nutrition therapy, regardless of the feeding route or perceived nutritional risk. Evidence has influenced clinical practice and guidelines, shifting toward less aggressive nutrition in the acute phase. European guidelines now recommend low-dose enteral nutrition within 48 hours of ICU admission, while American guidelines suggest either enteral or parenteral nutrition in the first 7–10 days. However, the optimal duration of the acute phase remains unclear, with differences between guidelines on the allowed time for below-target feeding. Micronutrient deficiencies are common in critically ill patients due to rapid depletion and increased utilization. Refeeding syndrome, a potentially life-threatening condition, can occur when micronutrient stores are low. Current guidelines recommend maintenance doses of micronutrients, but there is no validated standard for diagnosing refeeding syndrome. High pharmacological doses of individual micronutrients are not recommended as they have not been shown to be beneficial. Mechanisms explaining the lack of benefit from early high-dose nutrition include anabolic resistance, suppression of autophagy and ketogenesis, and increased stress hyperglycemia. Early full feeding may also lead to overfeeding and increased insulin needs. The time point when anabolic resistance switches into feeding responsiveness is unclear, making personalized nutrition challenging. Future research should focus on interventions beyond the acute phase and explore the role of indirect calorimetry in guiding energy dosing. Studies should also investigate the impact of optimizing nutritional intake in the post-acute phase on recovery and exercise. Additionally, the role of intermittent fasting/feeding strategies, ketogenic diets, and ketone supplementation