Macronutrient excess in critical illness: too much of a good thing?

PURPOSE OF REVIEW: Critical care nutrition has traditionally focused on preventing underfeeding, but recent evidence highlights the detrimental effects of early macronutrient excess exceeding metabolic capacity. Here we review recent advances elucidating mechanisms of macronutrient toxicity, clinical and biochemical markers of intolerance, and guideline-recommended strategies that tailor nutrient delivery to the patient's phase of illness. RECENT FINDINGS: Recent randomized controlled trials have suggested lack of benefit and even potential harm from early supplemental macronutrient supplementation in the ICU. Excess provision of energy, protein, carbohydrates, or lipids may exacerbate mitochondrial dysfunction, hyperglycaemia, hepatic steatosis, and immune impairment. These insights emphasize the need for developing biomarkers to guide precision nutrition in critically ill adults, aiming to optimize recovery and minimize metabolic complications. SUMMARY: Current evidence supports a phased, tolerance-based approach that avoids overfeeding during acute catabolism while supporting increased demands during recovery.