Towards a fasting-mimicking diet for critically ill patients: the pilot randomized crossover ICU-FM-1 study

Modulation of beta-hydroxybutyrate in traumatic brain injury

PURPOSE OF REVIEW

Traumatic brain injury (TBI) is a significant public health concern with substantial morbidity and mortality rates in the United States. Current management strategies primarily focus on symptomatic approaches and prevention of secondary complications. However, recent research highlights the potential role of ketone bodies, particularly beta-hydroxybutyrate (BHB), in modulating cellular processes involved in TBI. This article reviews the metabolism of BHB, its effect in TBI, and its potential therapeutic impact in TBI.

RECENT FINDINGS

BHB can be produced endogenously through fasting or administered exogenously through ketogenic diets, and oral or intravenous supplements. Studies suggest that BHB may offer several benefits in TBI, including reducing oxidative stress, inflammation, controlling excitotoxicity, promoting mitochondrial respiration, and supporting brain regeneration. Various strategies to modulate BHB levels are discussed, with exogenous ketone preparations emerging as a rapid and effective option.

SUMMARY

BHB offers potential therapeutic advantages in the comprehensive approach to improve outcomes for TBI patients. However, careful consideration of safety and efficacy is essential when incorporating it into TBI treatment protocols. The timing, dosage, and long-term effects of ketone use in TBI patients require further investigation to fully understand its potential benefits and limitations.

Impact of daily cyclic enteral nutrition versus standard continuous enteral nutrition in critically ill patients: a study protocol for a randomised controlled trial in three intensive care units in France (DC-SCENIC)

INTRODUCTION

Current guidelines on clinical nutrition of ventilated patients in the intensive care unit (ICU) recommend initiating continuous enteral nutrition within 48 hours of ICU admission when feasible. However, discontinuous feeding regimens, alternating feeding and fasting intervals, may have an impact on clinical and patient centred outcomes. The ongoing "Impact of daily cyclic enteral nutrition versus standard continuous enteral nutrition in critically ill patients" (DC-SCENIC) trial aims to compare standard continuous enteral feeding with daily cyclic enteral feeding over 10 hours to evaluate if implementing a fasting-mimicking diet can decrease organ failure in ventilated patients during the acute phase of ICU management.

METHODS AND ANALYSIS

DC-SCENIC is a randomised, controlled, multicentre, open-label trial comparing two parallel groups of patients 18 years of age or older receiving invasive mechanical ventilation and having an indication for enteral nutrition through a gastric tube. Enteral feeding is continuous in the control group and administered over 10 hours daily in the intervention group. Both groups receive isocaloric nutrition with 4 g of protein per 100 mL, and have the same 20 kcal/kg/day caloric target. The primary endpoint is the change in the Sequential Organ Failure Assessment score at 7 days compared with the day of inclusion in the study. Secondary outcomes include daily caloric and protein delivery, digestive, respiratory and metabolic tolerance as well as 28-day mortality, duration of mechanical ventilation and ventilator-free days. Outcomes will be analysed on an intention-to-treat basis. Recruitment started in June 2023 in 3 French ICU's and a sample size of 318 patients is expected by February 2026.

ETHICS AND DISSEMINATION

This study received approval from the national ethics review board on 8 November 2022 (Comité de Protection des Personnes Sud-Est VI, registration number 2022-A00827-36). Patients are included after informed consent. Results will be submitted for publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT05627167.

The metabolic effects of intermittent versus continuous feeding in critically ill patients

Intermittent (or bolus) feeding regimens in critically ill patients have been of increasing interest to clinicians and scientists. Changes in amino acid, fat and carbohydrate metabolites over time might yet deliver other benefits (e.g. modulation of the circadian rhythm and sleep, and impacts on ghrelin secretion, insulin resistance and autophagy). We set out to characterise these changes in metabolite concentration. The Intermittent versus Continuous Feeding in Critically Ill paitents study (NCT02358512) was an eight-centre single-blinded randomised controlled trial. Patients were randomised to received a continuous (control arm) or intermittent (6x/day, intervention arm) enteral feeding regimen. Blood samples were taken on trial days 1, 7 and 10 immediately before and 30 min after intermittent feeds, and at equivalent timepoints in the control arm. A pre-planned targeted metabolomic analysis was performend using Nuclear Resonance Spectroscopy. Five hundred and ninety four samples were analysed from 75 patients. A total of 24 amino acid-, 19 lipid based-, and 44 small molecule metabolite features. Across the main two axes of variation (40-60% and 6-8% of variance), no broad patterns distinguished between intermittent or continuous feeding arms, across intra-day sampling times or over the 10 days from initial ICU admission. Logfold decreases in abundance were seen in metabolites related to amino acids (Glutamine - 0.682; Alanine - 0.594), ketone body metabolism (Acetone - 0.64; 3-Hydroxybutyric Acid - 0.632; Acetonacetic Acid - 0.586), fatty acid (carnitine - 0.509) and carbohydrate metabolism ( Maltose - 0.510; Citric Acid - 0.485). 2-3 Butanediol, a by-product of sugar-fermenting microbial metabolism also decreased (- 0.489). No correlation was seen with change in quadriceps muscle mass for any of the 20 metabolites varying with time (all p > 0.05). Increasing severity of organ failure was related to increasing ketone body metabolism (3 Hydroxybutyric Acid-1 and - 3; p = 0.056 and p = 0.014), carnitine deficiency (p = 0.002) and alanine abundancy (p - 0.005). A 6-times a day intermittent feeding regimen did not alter metabolite patterns across time compared to continuous feeding in critically ill patients, either within a 24 h period or across 10 days of intervention. Future research on intermittent feeding regimens should focus on clinical process benefits, or extended gut rest and fasting.

Intermittent feeding with an overnight fast versus 24-h feeding in critically ill neonates, infants, and children: An open-label, single-centre, randomised controlled trial

BACKGROUND & AIMS

Critically ill children are fed day and night, assuming this improves enteral tolerance and the probability of achieving nutritional goals. It was previously shown that a fasting response, reflected by increased ketosis, at least partly explained the beneficial outcome of delayed initiation of supplemental parenteral nutrition. This study aims to investigate whether an overnight fast increases ketosis and is feasible and safe in critically ill children.

METHODS

The Continuousversus Intermittent Nutrition in Paediatric Intensive Care (ContInNuPIC) study is a randomised controlled trial in a tertiary referral Paediatric Intensive Care Unit (PICU) in the Netherlands. Critically ill children (term newborn-18 years) with an expected PICU stay ≥48 h, dependent on artificial nutrition, were eligible. Participants were randomly assigned (1:1, stratified for age group) to intermittent feeding, with interruption of feedings during an age-dependent overnight period of eight to 12 h, or to continuous feeding, with the administration of feedings day and night. In both groups, similar daily caloric targets were pursued. For children younger than one year, mandatory minor glucose infusions were provided during fasting. The primary outcome was the feasibility, defined as two conditions (1): a significant difference in the patients' highest daily ketone (3-β-hydroxybutyrate, BHB) levels during each overnight period, and (2): non-inferiority regarding daily caloric intake, examined using a two-part mixed-effects model with a predefined non-inferiority margin of 33%, in an intention-to-treat analysis. The study is registered in the Netherlands Trial Register (NL7877).

RESULTS

Between May 19, 2020, and July 13, 2022, 140 critically ill children, median (first quartile; third quartile) age 0.3 (0.1; 2.7) years, were randomised to intermittent (n = 67) or continuous feeding (n = 73). In the intermittent feeding group, BHB levels were significantly higher (median 0.4 (0.2; 1.0) vs. 0.3 (0.1; 0.7) mmol/L, p < 0.001). The ratio of total caloric intake in the intermittent feeding group to the intake in the continuous feeding group was not consistently significantly more than 0.67, thus not proving non-inferiority. No severe, resistant hypoglycaemic events, nor severe gastrointestinal complications related to the intervention occurred, and feeding intolerance did not occur more often in the intermittent than in the continuous feeding group.

CONCLUSION

Compared with day and night feeding, intermittent feeding with an overnight fast and mandatory glucose infusion for children younger than one year marginally increased ketosis and did not lead to more hypoglycaemic incidents in critically ill children. Because non-inferiority regarding daily caloric intake was not proven, the feasibility of an overnight fast could not be shown in the current study. However, as feeding intolerance did not increase during the condensed feeding periods, the nutritional intake was probably limited by the prescription of nutrition and interruptions. More research is needed to determine the optimal level and duration of clinically relevant ketosis and the best method to achieve this.

Personalized nutrition therapy in critical care: 10 expert recommendations

Personalization of ICU nutrition is essential to future of critical care. Recommendations from American/European guidelines and practice suggestions incorporating recent literature are presented. Low-dose enteral nutrition (EN) or parenteral nutrition (PN) can be started within 48 h of admission. While EN is preferred route of delivery, new data highlight PN can be given safely without increased risk; thus, when early EN is not feasible, provision of isocaloric PN is effective and results in similar outcomes. Indirect calorimetry (IC) measurement of energy expenditure (EE) is recommended by both European/American guidelines after stabilization post-ICU admission. Below-measured EE (~ 70%) targets should be used during early phase and increased to match EE later in stay. Low-dose protein delivery can be used early (~ D1-2) (< 0.8 g/kg/d) and progressed to ≥ 1.2 g/kg/d as patients stabilize, with consideration of avoiding higher protein in unstable patients and in acute kidney injury not on CRRT. Intermittent-feeding schedules hold promise for further research. Clinicians must be aware of delivered energy/protein and what percentage of targets delivered nutrition represents. Computerized nutrition monitoring systems/platforms have become widely available. In patients at risk of micronutrient/vitamin losses (i.e., CRRT), evaluation of micronutrient levels should be considered post-ICU days 5-7 with repletion of deficiencies where indicated. In future, we hope use of muscle monitors such as ultrasound, CT scan, and/or BIA will be utilized to assess nutrition risk and monitor response to nutrition. Use of specialized anabolic nutrients such as HMB, creatine, and leucine to improve strength/muscle mass is promising in other populations and deserves future study. In post-ICU setting, continued use of IC measurement and other muscle measures should be considered to guide nutrition. Research on using rehabilitation interventions such as cardiopulmonary exercise testing (CPET) to guide post-ICU exercise/rehabilitation prescription and using anabolic agents such as testosterone/oxandrolone to promote post-ICU recovery is needed.

Causes, Consequences, and Treatments of Sleep and Circadian Disruption in the ICU: An Official American Thoracic Society Research Statement

Background: Sleep and circadian disruption (SCD) is common and severe in the ICU. On the basis of rigorous evidence in non-ICU populations and emerging evidence in ICU populations, SCD is likely to have a profound negative impact on patient outcomes. Thus, it is urgent that we establish research priorities to advance understanding of ICU SCD. Methods: We convened a multidisciplinary group with relevant expertise to participate in an American Thoracic Society Workshop. Workshop objectives included identifying ICU SCD subtopics of interest, key knowledge gaps, and research priorities. Members attended remote sessions from March to November 2021. Recorded presentations were prepared and viewed by members before Workshop sessions. Workshop discussion focused on key gaps and related research priorities. The priorities listed herein were selected on the basis of rank as established by a series of anonymous surveys. Results: We identified the following research priorities: establish an ICU SCD definition, further develop rigorous and feasible ICU SCD measures, test associations between ICU SCD domains and outcomes, promote the inclusion of mechanistic and patient-centered outcomes within large clinical studies, leverage implementation science strategies to maximize intervention fidelity and sustainability, and collaborate among investigators to harmonize methods and promote multisite investigation. Conclusions: ICU SCD is a complex and compelling potential target for improving ICU outcomes. Given the influence on all other research priorities, further development of rigorous, feasible ICU SCD measurement is a key next step in advancing the field.

The need for biomarkers to determine response to enteral nutrition during and after critical illness: an update

PURPOSE OF REVIEW

Biomarkers proposed to provide prognosis or to determine the response to enteral nutrition have been assessed in a number of experimental and clinical studies which are summarized in the current review.

RECENT FINDINGS

There are several pathophysiological mechanisms identified which could provide biomarkers to determine response to enteral nutrition. Several biomarkers have been studied, most of them insufficiently and none of them has made its way to clinical practice. Available studies have mainly assessed a simple association of a biomarker with outcomes, but are less focused on dynamic changes in the biomarker levels. Importantly, studies on pathophysiology and clinical features of gastrointestinal dysfunction, including enteral feeding intolerance, are also needed to explore the mechanisms potentially providing specific biomarkers. Not only an association of the biomarker with any adverse outcome, but also a rationale for repeated assessment to assist in treatment decisions during the course of illness is warranted.

SUMMARY

There is no biomarker currently available to reliably provide prognosis or determine the response to enteral nutrition in clinical practice, but identification of such a biomarker would be valuable to assist in clinical decision-making.

Toward nutrition improving outcome of critically ill patients: How to interpret recent feeding RCTs?

Although numerous observational studies associated underfeeding with poor outcome, recent randomized controlled trials (RCTs) have shown that early full nutritional support does not benefit critically ill patients and may induce dose-dependent harm. Some researchers have suggested that the absence of benefit in RCTs may be attributed to overrepresentation of patients deemed at low nutritional risk, or to a too low amino acid versus non-protein energy dose in the nutritional formula. However, these hypotheses have not been confirmed by strong evidence. RCTs have not revealed any subgroup benefiting from early full nutritional support, nor benefit from increased amino acid doses or from indirect calorimetry-based energy dosing targeted at 100% of energy expenditure. Mechanistic studies attributed the absence of benefit of early feeding to anabolic resistance and futile catabolism of extra provided amino acids, and to feeding-induced suppression of recovery-enhancing pathways such as autophagy and ketogenesis, which opened perspectives for fasting-mimicking diets and ketone supplementation. Yet, the presence or absence of an anabolic response to feeding cannot be predicted or monitored and likely differs over time and among patients. In the absence of such monitor, the value of indirect calorimetry seems obscure, especially in the acute phase of illness. Until now, large feeding RCTs have focused on interventions that were initiated in the first week of critical illness. There are no large RCTs that investigated the impact of different feeding strategies initiated after the acute phase and continued after discharge from the intensive care unit in patients recovering from critical illness.

Intermittent feeding and circadian rhythm in critical illness

PURPOSE OF REVIEW

Circadian rhythms, i.e., periodic oscillations in internal biological processes, modulate metabolic processes such as hormonal signalling, nutrient absorption, and xenobiotic detoxification. Meal timing is a strong entraining cue for peripheral clocks in various organs, and eating out of circadian phases can impair glucose, gastrointestinal, and muscle metabolism. Sleep/wake cycles and circadian rhythms are extremely disrupted during critical illness. Timing of nutritional support may help preserve circadian rhythms and improve post-Intensive Care Unit (ICU) recovery. This review summarises circadian disruptors during ICU admission and evaluates the potential benefits of intermittent feeding on metabolism and circadian rhythms.

RECENT FINDINGS

Rhythmic expression of core clock genes becomes rapidly disturbed during critical illness and remains disturbed for weeks. Intermittent, bolus, and cyclic enteral feeding have been directly compared to routine continuous feeding, yet no benefits on glycaemic control, gastrointestinal tolerance, and muscle mass have been observed and impacts of circadian clocks remain untested.

SUMMARY

Aligning timing of nutritional intake, physical activity, and/or medication with circadian rhythms are potential strategies to reset peripheral circadian rhythms and may enhance ICU recovery but is not proven beneficial yet. Therefore, selecting intermittent feeding over continuous feeding must be balanced against the pros and cons of clinical practice.

When a calorie isn't just a calorie: a revised look at nutrition in critically ill patients with sepsis and acute kidney injury

PURPOSE OF REVIEW

To discuss how nutritional management could be optimized to promote protective metabolism in sepsis and associated acute kidney injury.

RECENT FINDINGS

Recent evidence suggests that sepsis is a metabolically distinct critical illness and that certain metabolic alterations, such as activation of fasting metabolism, may be protective in bacterial sepsis. These findings may explain the lack of survival benefit in recent randomized controlled trials of nutrition therapy for critical illness. These trials are limited by cohort heterogeneity, combining both septic and nonseptic critical illness, and the use of inaccurate caloric estimates to determine energy requirements. These energy estimates are also unable to provide information on specific substrate preferences or the capacity for substrate utilization. As a result, high protein feeding beyond the capacity for protein synthesis could cause harm in septic patients. Excess glucose and insulin exposures suppress fatty acid oxidation, ketogenesis and autophagy, of which emerging evidence suggest are protective against sepsis associated organ damage such as acute kidney injury.

SUMMARY

Distinguishing pathogenic and protective sepsis-related metabolic changes are critical to enhancing and individualizing nutrition management for critically ill patients.

Novel insights in endocrine and metabolic pathways in sepsis and gaps for future research

Sepsis is defined as any life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains an important cause of critical illness and has considerable short- and long-term morbidity and mortality. In the last decades, preclinical and clinical research has revealed a biphasic pattern in the (neuro-)endocrine responses to sepsis as to other forms of critical illness, contributing to development of severe metabolic alterations. Immediately after the critical illness-inducing insult, fasting- and stress-induced neuroendocrine and cellular responses evoke a catabolic state in order to provide energy substrates for vital tissues, and to concomitantly activate cellular repair pathways while energy-consuming anabolism is postponed. Large randomized controlled trials have shown that providing early full feeding in this acute phase induced harm and reversed some of the neuro-endocrine alterations, which suggested that the acute fasting- and stress-induced responses to critical illness are likely interlinked and benefical. However, it remains unclear whether, in the context of accepting virtual fasting in the acute phase of illness, metabolic alterations such as hyperglycemia are harmful or beneficial. When patients enter a prolonged phase of critical illness, a central suppression of most neuroendocrine axes follows. Prolonged fasting and central neuroendocrine suppression may no longer be beneficial. Although pilot studies have suggested benefit of fasting-mimicking diets and interventions that reactivate the central neuroendocrine suppression selectively in the prolonged phase of illness, further study is needed to investigate patient-oriented outcomes in larger randomized trials.

A systematic analysis of diet-induced nephroprotection reveals overlapping changes in cysteine catabolism

Caloric Restriction (CR) extends lifespan and augments cellular stress-resistance from yeast to primates, making CR an attractive strategy for organ protection in the clinic. Translation of CR to patients is complex, due to problems regarding adherence, feasibility, and safety concerns in frail patients. Novel tailored dietary regimens, which modulate the dietary composition of macro- and micronutrients rather than reducing calorie intake promise similar protective effects and increased translatability. However, a direct head-to-head comparison to identify the most potent approach for organ protection, as well as overlapping metabolic consequences have not been performed. We systematically analyzed six dietary preconditioning protocols - fasting mimicking diet (FMD), ketogenic diet (KD), dietary restriction of branched chained amino acids (BCAA), two dietary regimens restricting sulfur-containing amino acids (SR80/100) and CR - in a rodent model of renal ischemia-reperfusion injury (IRI) to quantify diet-induced resilience in kidneys. Of the administered diets, FMD, SR80/100 and CR efficiently protect from kidney damage after IRI. Interestingly, these approaches show overlapping changes in oxidative and hydrogen sulfide (H₂S)-dependent cysteine catabolism as a potential common mechanism of organ protection.

Continuous versus Intermittent Nutrition in Pediatric Intensive Care patients (ContInNuPIC): a study protocol for a randomized controlled trial (Preprint)

Background

Objective

Methods

Results

Conclusions

Trial Registration

International Registered Report Identifier (IRRID)

Impact of tight glucose control on circulating 3-hydroxybutyrate in critically ill patients

BACKGROUND

Recent evidence suggests a potentially protective effect of increasing ketone body availability via accepting low macronutrient intake early after onset of critical illness. The impact of blood glucose control with insulin on circulating ketones is unclear. Whereas lowering blood glucose may activate ketogenesis, high insulin concentrations may have the opposite effect. We hypothesized that the previously reported protective effects of tight glucose control in critically ill patients receiving early parenteral nutrition may have been mediated in part by activation of ketogenesis.

METHODS

This is a secondary analysis of 3 randomized controlled trials on tight versus liberal blood glucose control in the intensive care unit, including 700 critically ill children and 2748 critically ill adults. All patients received early parenteral nutrition as part of the contemporary standard of care. Before studying a potential mediator role of circulating ketones in improving outcome, we performed a time course analysis to investigate whether tight glucose control significantly affected ketogenesis and to identify a day of maximal effect, if any. We quantified plasma/serum 3-hydroxybutyrate concentrations from intensive care unit admission until day 3 in 2 matched subsets of 100 critically ill children and 100 critically ill adults. Univariable differences between groups were investigated by Kruskal-Wallis test. Differences in 3-hydroxybutyrate concentrations between study days were investigated by Wilcoxon signed-rank test.

RESULTS

In critically ill children and adults receiving early parenteral nutrition, tight glucose control, as compared with liberal glucose control, lowered mean morning blood glucose on days 1-3 (P < 0.0001) via infusing insulin at a higher dose (P < 0.0001). Throughout the study period, caloric intake was not different between groups. In both children and adults, tight glucose control did not affect 3-hydroxybutyrate concentrations, which were suppressed on ICU days 1-3 and significantly lower than the ICU admission values for both groups (P < 0.0001).

CONCLUSION

Tight versus liberal glucose control in the context of early parenteral nutrition did not affect 3-hydroxybutyrate concentrations in critically ill patients. Hence, the protective effects of tight glucose control in this context cannot be attributed to increased ketone body availability.

Intermittent fasting in paediatric critical illness: The properties and potential beneficial effects of an overnight fast in the PICU

Although evidence for the superiority of continuous feeding over intermittent feeding is lacking, in most paediatric intensive care units (PICU) artificial feeding is administered continuously for 24 h per day. Until now, studies in PICU on intermittent feeding have primarily focused on surrogate endpoints such as nutritional intake and gastro-intestinal complaints and none have studied the effects of an extended fasting period. Intermittent fasting has been proven to have many health benefits in both animal and human studies. The observed beneficial effects are based on multiple metabolic and endocrine changes that are presumed crucial in critical illness as well. One key element is the transition to ketone body metabolism, which, among others, contributes to the stimulation of several cellular pathways involved in stress resistance (neuro)plasticity and mitochondrial biogenesis, and might help preserve brain function. Secondly, the fasting state stimulates the activation of autophagy, a process that is crucial for cellular function and integrity. Of the different intermittent fasting strategies investigated, time-restricted feeding with a daily extended fasting period appears most feasible in the PICU. Moreover, planning the fasting period overnight could help maintain the circadian rhythm. Although not investigated, such an overnight intermittent fasting strategy might improve the metabolic profile, feeding tolerance and perhaps even have beneficial effects on tissue repair, reperfusion injury, muscle weakness, and the immune response. Future studies should investigate practical implications in critically ill children and the optimal duration of the fasting periods, which might be affected by the severity of illness and by age.

Role of ketones, ketogenic diets and intermittent fasting in ICU

PURPOSE OF REVIEW

To summarize the clinical evidence for beneficial effects of ketones, ketogenic diets and intermittent fasting in critical illness, and to review potential mechanisms behind such effects.

RECENT FINDINGS

Recent evidence demonstrates that activation of a metabolic fasting response may be beneficial to recover from critical insults. Potential protective mechanisms are, among others, activation of ketogenesis and of damage removal by autophagy. Novel feeding strategies, including ketone supplements, ketogenic diets and intermittent fasting regimens, can activate these pathways - at least partially - in critically ill patients. Randomized controlled trials (RCTs) studying these novel feeding strategies as compared with standard care, are scarce and have not shown consistent benefit. Yet, all RCTs were small and underpowered for clinical endpoints. Moreover, in intermittent fasting studies, the duration of the fasting interval may have been too short to develop a sustained metabolic fasting response.

SUMMARY

These findings open perspectives for the further development of fasting-mimicking diets. Ultimately, clinical benefit should be confirmed by RCTs that are adequately powered for clinically relevant, patient-centered endpoints.

Parenteral nutrition in critical illness: total, supplemental or never?

PURPOSE OF REVIEW

The current review summarizes recent evolutions in knowledge and discusses the concept of whom and when parenteral nutrition should be considered in critically ill patients as a total form of nutrition, in a supplemental form, or never.

RECENT FINDINGS

Recent developments in our understanding of the application of parenteral nutrition in critical care include the phases of illness, avoidance of overfeeding and the population in whom parenteral nutrition may be appropriate for. Importantly, one of the greatest lessons of recent times may be who not to provide parenteral nutrition to; however, a blanket approach of increased risk with parenteral nutrition is too simple for the modern context.

SUMMARY

When providing total or supplemental parenteral nutrition, avoidance of overfeeding with total calories and/or glucose alone is critical, as is consideration to the phase of illness the patient is in, the population in whom it is to be applied, premorbid nutrition status and the setting (including adequacy of line management and expertise in parenteral nutrition provision). The appropriateness of parenteral nutrition should be considered in those where death is imminent or who are well nourished, likely to commence oral and/or enteral nutrition imminently and have a short-stay in intensive care, or are in a high-risk setting.

Are periods of feeding and fasting protective during critical illness?

PURPOSE OF REVIEW

To review the mechanisms how intermittent feeding regimens could be beneficial in critically ill patients.

RECENT FINDINGS

Large randomized controlled trials (RCTs) have failed to demonstrate consistent benefit of early, enhanced nutritional support to critically ill patients, and some trials even found potential harm. Although speculative, the absence of a clear benefit could be explained by the continuous mode of feeding in these trials, since intermittent feeding regimens had health-promoting effects in healthy animals and humans through mechanisms that also appear relevant in critical illness. Potential protective mechanisms include avoidance of the muscle-full effect and improved protein synthesis, improved insulin sensitivity, better preservation of circadian rhythm, and fasting-induced stimulation of autophagy and ketogenesis. RCTs comparing continuous versus intermittent feeding regimens in critically ill patients have shown mixed results, albeit with different design and inclusion of relatively few patients. In all studies, the fasting interval was relatively short (4-6 h maximum), which may be insufficient to develop a full fasting response and associated benefits.

SUMMARY

These findings open perspectives for the design and clinical validation of intermittent feeding regimens for critically ill patients. The optimal mode and duration of the fasting interval, if any, remain unclear.