Low-Calorie Feeding Does Not Worsen Kidney Function in Shock

The Metabolic Tightrope of Critical Care Nutrition

Determining the optimal nutritional strategy for critically ill patients remains a persistent clinical challenge, particularly during the acute phase of shock when organ perfusion is severely compromised [1]. While adequate caloric and protein intake is essential for long-term recovery, aggressive early feeding can impose a significant metabolic burden on vulnerable organs, potentially exacerbating ischemia-reperfusion injuries and cellular stress [2]. Consequently, intensivists must carefully balance the risks of malnutrition against the dangers of metabolic overload, relying on robust randomized controlled trials to navigate these complex physiological trade-offs [1, 3]. The impact of early protein and calorie targets on acute renal function has remained a subject of intense debate, as the kidneys are highly sensitive to both hypoperfusion and the accumulation of metabolic waste products. A new analysis of 3,036 mechanically ventilated patients with shock now offers critical clarity, demonstrating that early low-calorie and low-protein nutrition (6 kcal/kg and 0.2 to 0.4 g protein/kg/day) for seven days does not increase acute kidney disease incidence compared to standard feeding (44.6 percent versus 46.1 percent; hazard ratio, 0.97; 95 percent confidence interval, 0.88 to 1.07; P = 0.53) [4].

Defining Nutritional Targets in the NUTRIREA-3 Cohort

The optimal intake of artificial nutrition in critically ill patients remains unclear in daily clinical practice. While physicians recognize that calorie and protein intakes affect glomerular function in patients with chronic kidney disease, their relation to renal function at the acute phase of intensive care is insufficiently documented. To address this knowledge gap, researchers aimed to evaluate the specific associations of a low-calorie and low-protein diet with renal outcomes in critically ill patients. The investigators conducted a post hoc analysis (a retrospective evaluation of data gathered during a previously completed trial) of the NUTRIREA-3 randomized controlled trial to test these nutritional strategies. The analysis included 3,036 mechanically ventilated patients with shock. Participants received either low or standard calorie and protein intakes during the first seven days of their admission. The low intake group was restricted to 6 kcal/kg and 0.2 to 0.4 g protein/kg/day. In contrast, the standard intake group received 25 kcal/kg and 1.0 to 1.3 g protein/kg/day. To measure the impact of these early feeding strategies, the primary outcome was defined as the incidence of acute kidney disease during the intensive care unit (ICU) stay. The researchers tracked this metric throughout an observation period that lasted up to ICU discharge or day 90 after inclusion, whichever occurred first.

Primary Renal Outcomes and Urea Reduction

When evaluating the primary endpoint, the researchers found that early nutritional restriction did not alter the trajectory of acute kidney disease. Acute kidney disease during the ICU stay occurred in 669 (44.6 percent) patients in the low-calorie and low-protein group. This incidence closely mirrored the standard feeding cohort, where acute kidney disease during the ICU stay occurred in 691 (46.1 percent) patients in the standard group. Statistical analysis confirmed this equivalence, showing that the hazard ratio (a measure of how often a particular event happens in one group compared to another over time) for acute kidney disease between the low and standard groups was 0.97 (95 percent confidence interval 0.88 to 1.07; P = 0.53). For practicing intensivists, these data indicate that withholding standard caloric and protein targets during the initial phase of shock does not increase the risk of acute renal impairment. While the incidence of clinical kidney disease remained stable across both cohorts, the restricted diet did produce expected biochemical shifts in nitrogenous waste accumulation. The highest urea level was significantly lower in the low-calorie and low-protein group (P = 0.002), reflecting the reduced metabolic burden of processing exogenous amino acids. This reduction persisted throughout the acute care period, as the urea level at ICU discharge was significantly lower in the restricted group (P = 0.002). However, these lower urea concentrations did not translate into tangible clinical benefits or harms regarding advanced organ support. The study demonstrated that there were no differences between groups regarding renal replacement therapy requirements. Additionally, there were no differences between groups for other renal outcomes, confirming that the observed variations in urea were merely a physiological reflection of protein intake rather than a marker of altered intrinsic kidney function.

Safety Across High-Risk Subgroups

To determine if specific vulnerable populations might be harmed by nutritional restriction, the researchers evaluated several high-risk cohorts. They found that the safety profile of the restricted diet was maintained, as the results were similar in patients with early kidney dysfunction. The equivalence between the two feeding strategies remained consistent across other critically ill subsets, demonstrating that the results were similar in patients with severe organ failures. Importantly for clinicians managing chronic comorbidities in the intensive care unit, the results were similar in patients with end-stage chronic kidney disease. The overarching clinical takeaway from this analysis is that early low-calorie and low-protein nutrition for seven days was not associated with worse renal outcomes compared to standard feeding in critically ill patients with shock. Beyond kidney-specific metrics, the restricted diet proved safe overall, as early low-calorie and low-protein nutrition for seven days was not associated with worse mortality compared to standard feeding. For practicing physicians, these findings provide robust reassurance that a conservative feeding strategy during the acute phase of shock does not compromise patient survival or organ recovery. Crucially, the lack of association with worse renal outcomes or mortality held true even in patients with preexisting renal dysfunction, allowing intensivists to prioritize metabolic stability without fearing iatrogenic harm to already vulnerable kidneys.

References

1. McClave SA, Taylor B, Martindale RG, et al. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient. Journal of Parenteral and Enteral Nutrition. 2016. doi:10.1177/0148607115621863

2. Zhang M, Liu Q, Meng H, et al. Ischemia-reperfusion injury: molecular mechanisms and therapeutic targets. Signal Transduction and Targeted Therapy. 2024. doi:10.1038/s41392-023-01688-x

3. Deaton A, Cartwright N. Understanding and misunderstanding randomized controlled trials. Social Science & Medicine. 2017. doi:10.1016/j.socscimed.2017.12.005

4. Schleef M, Mayet V, Gouge AL, et al. Low versus standard calorie and protein feeding and renal dysfunction in ventilated adults with shock: a NUTRIREA-3 post hoc analysis.. Intensive care medicine. 2026. doi:10.1007/s00134-026-08369-7