Circadian rhythms, metabolism, and nutrition support in critically ill adult patients: a narrative review

PURPOSE OF REVIEW: The human circadian system regulates several physiological processes, including metabolism, which becomes significantly disrupted during critical illness. The common use of 24-h continuous nutrition support feeding in the intensive care unit (ICU) may further exacerbate these disruptions; this review evaluates recent evidence comparing continuous and intermittent feeding schedules in critically ill adults. RECENT FINDINGS: Research comparing different feeding schedules in critically ill adults remains limited. Recent meta-analyses suggest that continuous and intermittent feeding schedules in the ICU have comparable adverse event profiles, including gastrointestinal intolerance. A retrospective study found that continuous feeding did not impact the 24-h glucose variation in critically ill adults, and a randomized controlled trial reported no significant differences in amino acid, lipid-based, or small molecule metabolite profiles between the two feeding regimens. Potential benefits of intermittent feeding include stimulation of muscle protein synthesis, preservation of normal hormone secretion, and improved attainment of nutritional goals. SUMMARY: Current evidence suggests comparable safety profiles for continuous and intermittent feeding schedules in critically ill adult patients. However, intermittent and daytime cyclic feeding are expected to align more closely with normal circadian physiology. Given the lack of existing supportive data, a dynamic approach - transitioning from continuous feeding in the early-acute metabolic phase to intermittent feeding or daytime cyclic feeding - may be appropriate.