REVIEW

C URRENT
OPINION Current insights in ICU nutrition: tailored nutrition
Anoek Jacqueline Hubertine Hermans a,b,
, Babette Irene Laarhuis a,
,
Imre Willemijn Kehinde Kouw b and Arthur Raymond Hubert van Zanten a,b

Purpose of review
To summarize recent research on critical care nutrition focusing on the optimal composition, timing, and
monitoring of enteral feeding strategies for (post)-ICU patients. We provide new insights on energy and
protein recommendations, feeding intolerance, and describe nutritional practices for coronavirus disease
2019 ICU patients.
Recent findings
The use of indirect calorimetry to establish individual energy requirements for ICU patients is considered the
gold standard. The limited research on optimal feeding targets in the early phase of critical illness suggests
avoiding overfeeding. Protein provision based upon the absolute lean body mass is rational. Therefore,
body composition measurements should be considered. Body impedance analysis and muscle ultrasound
seem reliable, affordable, and accessible methods to assess body composition at the bedside. There is
inadequate evidence to change our practice of continuous enteral feeding into intermittent feeding. Finally,
severe acute respiratory syndrome coronavirus 2 patients are prone to underfeeding due to
hypermetabolism and should be closely monitored.
Summary
Nutritional therapy should be adapted to the patient’s characteristics, diagnosis, and state of metabolism
during ICU stay and convalescence. A personalized nutrition plan may prevent harmful over- or
underfeeding and attenuate muscle loss. Despite novel insights, more research is warranted into tailored
nutrition strategies during critical illness and convalescence.
Keywords
body impedance analysis, energy, intensive care, proteins, timing

INTRODUCTION COMPOSITION OF ENTERAL NUTRITION

Critical care nutrition is a rapidly evolving field Nutrition provision, matching an individual’s
in which significant steps have been made toward needs, is crucial to enhance recovery and decrease
nutritional recommendations specific to each complications in critical illness. The appropriate
patient. This shift allows healthcare providers to composition of enteral nutrition (EN) includes
consider the patient’s characteristics, medical diag-
nosis, current treatments, and metabolic state [1].
The multifactorial nature of nutritional needs in a
Department of Intensive Care Medicine, Gelderse Vallei Hospital, Ede
critically ill patients and the difference in outcomes and bWageningen University & Research, Division of Human Nutrition
and methodologies assessed in available studies pose and Health, Wageningen, The Netherlands
challenges to establishing fitting guidelines. Correspondence to Professor Arthur Raymond Hubert van Zanten, MD,
This narrative review aims to summarize the PhD, Chair Department of Intensive Care Medicine & Research, Gel-
latest updates on nutritional practices in the ICU. derse Vallei Hospital, Willy Brandtlaan 10, 6716 RP Ede, The Nether-
It focuses on energy content, protein provision, mode lands. E-mail: zantena@zgv.nl and Division of Human Nutrition and
Health, chair group Nutritional Biology, Wageningen University &
of enteral feeding, and timing of enteral nutrition. Research, HELIX (Building 124), Stippeneng 4, 6708 WE Wageningen,
Also, the latest insights into nutritional strategies for The Netherlands. E-mail: Arthur.vanzanten@wur.nl
severe acute respiratory syndrome coronavirus 2

Drs Hermans and Laarhuis contributed equally to this work.
(SARS-CoV-2)-infected ICU patients are addressed. Curr Opin Crit Care 2023, 29:101–107
Finally, as enteral feeding intolerance (FI) is associ-
DOI:10.1097/MCC.0000000000001016
ated with worse outcomes, such as higher mortality
This is an open access article distributed under the Creative Commons
and fewer ventilator-free days [2], clinical implica- Attribution License 4.0 (CCBY), which permits unrestricted use, dis-
tions and treatment of FI according to the latest tribution, and reproduction in any medium, provided the original work is
nutritional recommendations are evaluated. properly cited.

1070-5295 Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. www.co-criticalcare.com
Gastrointestinal system

protein delivery was not associated with muscle

KEY POINTS loss [6]. Another retrospective multicentre database
 Personalized nutrition is paramount to providing study (N ¼ 21 100) that compared a standard (0.8–
nutrients adapted to the patient’s situation, disease such 1.2 g/kg/day) vs. low protein diet (<0.8 g/kg/day)
as coronavirus disease 2019, and phase. showed a lower hospital mortality in patients that
received a late standard protein diet (0.8–1.2 g/kg/
 Energy provision guided by indirect calorimetry may
day) vs. patients that received a continuously low
improve outcomes, although gradually increasing the
energy intake over the initial ICU days is essential to protein diet (<0.8 g/kg/day). This benefit was not
prevent overfeeding. further exaggerated in the group that received a late
high protein diet (>1.2 g/kg/day) [7].
 Lean body mass measured through bioelectrical Findings align with a recent meta-analysis of 19
impedance or ultrasound facilitates calculating
RCTs that compared higher vs. lower protein deliv-
individual protein goals for overweight and
obese patients. ery (with matched energy delivery between groups)
on clinical and patient-centred outcomes showing
 Feeding intolerance is common and can often be no further improvement in physical function and
treated successfully, while there is no evidence of mortality in response to high-protein diets. It must
superiority of intermittent feeding over continuous
be noted that the nutritional goals in the included
enteral feeding.
RCTs were often not met, with intake ranges varying
 Post-ICU nutrition intake is poor, particularly when the from 0.9 to 2.6 g/kg/day. The relatively low protein
feeding tube is removed early. intake in these ‘high-protein’ groups complicates
the comparison to retrospective data. Moreover,
some studies delivered total protein goals on the
adequate amounts of energy, specific macronu- first ICU day, whereas others gradually increased
trient composition, and the addition of essential protein provision in the early phase.
micronutrients. However, in five studies, associations between
protein provision and muscle loss suggested that
higher protein delivery attenuated skeletal muscle
PROTEIN PROVISION loss by 3.4% per week [8 ]. In health, muscle mass
&&

Catabolism in critical illness is known to encompass declined under high protein provision without
proteolysis of body proteins, resulting in rapid loss resistance training and increased when high resist-
of muscle mass. Muscle wasting leads to muscle ance training was added to the regimen [9]. There-
weakness and impaired metabolic health. Decreased fore, early resistance training might preserve muscle
functional performance has been observed in ICU mass and mitigate muscle loss during critical illness.
survivors up to multiple years post-ICU [3]. Quantifying amino acid balance during ICU
Muscle mass maintenance is regulated through admission and assessing whole-body and muscle
muscle protein synthesis and breakdown rates, with protein metabolism in response to increased protein
periods of muscle protein anabolism being key to intakes provides mechanistic insight into the
maintaining muscle mass. Dietary protein is an muscle protein anabolic capacity in ICU patients
&
anabolic stimulus for muscle protein synthesis in [10 ]. Contemporary stable isotope methodology
healthy subjects. Therefore, augmented protein assessing whole-body and muscle protein anabolic
intake has been suggested as an effective strategy response to protein delivery has only been addressed
to attenuate muscle wasting. Observational studies by a few studies [11], as this technique is expensive,
have shown higher protein delivery to improve labour-intensive, and requires repeated blood sam-
clinical outcomes, for example, reduced mortality. pling and skeletal muscle tissue collection [12].
&
Therefore, international guidelines recommend a Chapple et al. [10 ] quantified postprandial protein
protein provision of 1.2–2.0 g/kg/day [4,5]. How- handling in response to duodenal protein feeding in
ever, these guidelines have been based on retrospec- ICU patients and BMI and age-matched healthy
tive and prospective cohort studies, lacking data on control subjects. Although dietary amino acid
the effect of protein provision on functional and uptake was similar between groups, the deposition
metabolic outcomes. of dietary amino acids into myofibrillar protein was
A recent retrospective study by Lambell et al. 60% lower after the protein bolus. This study dem-
analysed protein provision and muscle mass loss onstrates profound skeletal muscle anabolic resist-
(assessed by using CT-derived skeletal muscle area). ance in critical illness, likely contributing to muscle
Although skeletal muscle area declined over the first wasting. Whether higher protein provision can
three weeks of ICU stay, with protein provision overcome this critical illness anabolic resistance
averaging 1.1 g/kg/day (and 83% being achieved), warrants further studies.

102 www.co-criticalcare.com Volume 29  Number 2  April 2023

 Current insights in ICU nutrition: tailored nutrition Hermans et al.

More studies have been conducted to assess IC does not account for endogenous energy
protein needs with the increasing availability of production, noninhibitable by exogenous feeding
bedside body composition measurements. Interna- or insulin, typically present in the early phase. No
tional guidelines have recently recommended reliable bedside method to assess this production
assessing lean body mass (LBM) to determine pro- has been established yet. Therefore, indirect calo-
tein goals in obese and overweight patients [4]. rimetry remains the preferred method to assess
Several predictive formulas provide estimations of energy needs after the initial phase of high endog-
LBM) and can differ significantly from actual LBM enous energy production has resolved [19,20]. If
&
[13 ]. LBM or muscle mass can be better estimated indirect calorimetry is unavailable, VCO2 measure-
using Dual-energy X-ray absorptiometry, CT or MRI ments (kcal/24 h ¼ VCO2  8.19) are slightly more
scans. However, these methods are impractical or accurate than predictive formulas [4]. However, in a
impossible to implement at the bedside, are costly study from our group, VCO2 overestimates the
&
and cannot be repeated regularly [14]. actual EE compared to indirect calorimetry [21 ].
Bioelectric impedance analysis (BIA) is a more
affordable and practical method to assess LBM in
ICU patients. While fluid overload can introduce TIMING AND NUTRITION TARGETS
variations in measurements [14], multifrequency Besides the macronutrient composition of EN, the
BIA can assess the extracellular water surplus, which timing of nutritional provision is important as
can be adjusted to prevent LBM overestimation [15]. energy and protein needs vary over stages of
Bedside ultrasonography is an alternative to assess critical illness.
LBM but more operator-dependent.
High protein provision (i.e., >1.2 g/kg/day) has
not yet been proven to improve clinical endpoints PREVENTION OF OVERFEEDING IN THE
compared to lower intake levels in ICU patients. EARLY PHASE
However, it may attenuate muscle loss. Assessment During the early phase of critical illness, endoge-
of LBM by BIA is recommended, especially in obese nous energy production is estimated to be 500–
and overweight patients. Areas that remain to be 1400 kcal/day. Therefore, guidelines recommend
investigated are combining high protein provision gradually increasing energy intake over several days
with early resistance therapy, reliable and afford- up to 80–100% of the REE to prevent overfeeding.
able methods to assess muscle anabolism, and prac- In observational studies, a hypocaloric intake of
tical methods to assess the whole-body protein 70–80% of the REE in the early phase of critical
balance. illness was associated with reduced mortality [4].
Conversely, the majority of RCTs did not confirm
these observations. A recent systematic review by
ENERGY INTAKE AND ENERGY &
Zhou et al. [22 ] observed no effect of hypocaloric
EXPENDITURE feeding in the early phase of critical illness, with
Determining energy requirements is essential to matched protein intake levels, on mortality and ICU
prevent harmful under- and overfeeding. However, or hospital length of stay. However, this systematic
the optimal amount of energy provision remains review included studies using predictive formulas
debatable. Energy expenditure (EE) may vary during and IC-derived measurements to calculate EE.
different phases of critical illness. The nutritional Future studies using only IC-derived EE are
status and endogenous energy production account needed to elucidate the need and exact timing of
for significant proportions of energy substrate (hypocaloric) feeding in early critical illness.
during early critical illness. The resting energy
expenditure (REE) can be measured using indirect
calorimetry (IC). As ICU patients typically engage in FEEDING MODALITIES
minimal physical activity, REE will be close to the The mode of enteral feeding has been debated for
total energy expenditure (TEE). Predictive formulas years. Commonly used enteral feeding modalities
differ significantly from indirect calorimetry REE include continuous (24 h/day), intermittent, bolus,
and can lead to deviations up to 1000 kcal/day from or cyclic feeding [23]. Although international guide-
&&
the actual EE [16]. Duan et al. [17 ] showed that IC- lines recommend continuous feeding, this recom-
guided energy delivery reduces short-term mortality mendation is based on limited evidence [4].
&
by 23%, probably by preventing harmful under- or A recent RCT by Lee et al. [24 ] demonstrated
overfeeding. However, the recent TICACOS-II trial improved feeding adequacy among patients with
could not reproduce this mortality effect, although continuous feeding; >80% of the nutritional target
underpowering may have played a role [18]. was reached more frequently in the continuous vs.

1070-5295 Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. www.co-criticalcare.com 103
Gastrointestinal system

the intermittent feeding group (65.0% vs. 52.4%). which poses challenges for research [32]. A recent
However, a recent systematic review observed no systematic review addressed various definitions used
differences in nutritional intake, mortality, or gas- in studies to define FI. It is described as high GRV or
trointestinal intolerance between continuous and other gastrointestinal (GI) symptoms; however, dif-
intermittent feeding [25]. During continuous feed- ferent cut-off points for volumes and combinations
ing, the slow release of nutrients into the stomach is with clinical symptoms cause intra-study variety
&&
thought to reduce feeding tolerance, the risk of [33 ]. Furthermore, Blaser et al. [32] recommend
regurgitation, and respiratory complications. How- that the FI-definition should comprise intake
ever, while intermittent feeding has been suggested <80% of the target within the first 72 h of EN
to increase feeding intolerance (FI), gastric residual initiation and the presence of at least one GI-symp-
volume (GRV), and aspiration risk, there is no evi- tom while considering the optimization of non-EN-
dence showing that aspiration risk is higher in related factors (e.g., medication, GI-infection, and
&&
patients on intermittent feeding [26 ]. bowel anatomy).
Moreover, intermittent feeding is considered FI has been shown to be associated with worse
more physiological as it mimics regular eating pat- clinical outcomes, such as fewer ventilator-free days,
terns, potentially maintaining regular gastrointesti- extended ICU stay, and higher mortality rates
nal hormone secretion and digestion [27]. It may [31,34]. However, numerous strategies to impact
increase gut motility and enhance the release of FI and improve nutrition delivery have been pro-
postprandial gastrointestinal hormones and incre- posed. In a posthoc analysis of the TARGET-trial,
tins involved in glucose control. However, no stud- patients with GRV >250 ml showed lower mortality
ies have compared strategies on gastric emptying rates when treated with prokinetics [34]. Con-
and glucoregulatory hormone release in ICU versely, in a meta-analysis, prokinetics did not lower
patients. Studies that have assessed the effect of mortality. However, reduced lengths of ICU and
&
intermittent feeding on glycaemic variability show hospital stay were found [35 ]. Prebiotics, probiotics,
either increased glycaemic variability [28] or no or synbiotics do not significantly affect FI [36].
differences in blood glucose levels [29]. These stud- Moreover, energy-dense enteral feeds have resulted
ies assessed 4–6 hourly glucose levels. Real-time in a higher incidence of FI [34]. A recent meta-
continuous glucose monitoring may provide more analysis showed that postpyloric feeding was asso-
insight into the glycaemic response and variability. ciated with fewer GI complications, increased feed-
Noncontinuous feeding may attenuate muscle ing adequacy, and reduced mechanical ventilation
wasting due to increased plasma amino acid avail- and ICU stay duration, although no difference in
&
ability leading to increased muscle protein synthesis mortality was shown [37 ]. Thus, treatment with
rates [28]. However, no studies have assessed the prokinetics and administering postpyloric feeding
effect of bolus feeding on muscle metabolism in in patients not responding to prokinetics should be
critically ill patients. Meal timing has been shown considered when FI emerges. A uniform definition
to play an essential role in metabolic health by of FI is urgently needed.
preserving circadian rhythms in overweight, obese,
or type 2 diabetes patients. With circadian rhythms
being largely disrupted during critical illness, inter- NUTRITION IN CORONAVIRUS DISEASE
mittent or cyclic feeding might effectively preserve 2019
circadian alignment [30]. Moreover, prolonged peri- The SARS-CoV-2 pandemic warranted research for
ods of fasting lead to improved glucose control, specific nutritional strategies in the ICU. In approx-
insulin sensitivity, improved lipid profiles, and imately 56% of COVID-19 ICU patients, FI was
the activation of ketogenesis and autophagy in present, and 52% of patients suffered from malnu-
healthy individuals. Nonetheless, this remains to trition. Among other factors, the hypermetabolic
be investigated in critically ill patients. Without and prolonged catabolic state of COVID-19 patients
evidence of the superiority of intermittent feeding, make personalized and accurate nutrition treatment
&&
there is no reason to change our practice of con- essential [38 ,39]. Furthermore, SARS-CoV-2 can
tinuous feeding in the ICU. attack the mucosal epithelium and cause gastroin-
testinal symptoms, increasing FI and malnutrition
risk [40].
FEEDING INTOLERANCE Early enteral nutrition, within 24–36 h of ICU
Enteral FI is frequently encountered, especially in admission or 12 h of intubation, showed to reduce
the early phase of ICU admission, potentially result- mortality of COVID-19 ICU patients in a systematic
ing in insufficient absorption of nutrients [31]. review. However, no significant differences in the
Nevertheless, a uniform definition of FI is lacking, length of ICU and hospital stay or mechanical

104 www.co-criticalcare.com Volume 29  Number 2  April 2023

 Current insights in ICU nutrition: tailored nutrition Hermans et al.

&&
ventilation duration were observed [41 ]. Patients leads to an immediate decrease in daily energy
with an increased malnutrition risk, such as older (44.1%) and protein (50.7%) intake, suggesting that
and polymorbid patients, should be identified and EN tapering protocols and introduction of ONS after
treated accordingly. Supplementation of vitamins tube removal are essential to optimize nutritional
and trace elements, physical activity, oral nutri- intake during ICU recovery. The causes of inad-
tional supplements (ONS), and EN should be admin- equate intake should be evaluated. Nutrient intake
istered if necessary [42]. must be monitored, and continuity of nutritional
treatment in the post-ICU phase in general wards
and at home should be guaranteed.
POST-ICU NUTRITION
No formal guidelines on nutrition therapy for post-
ICU patients are available. However, energy and CONCLUSION
protein intake should likely be further increased Nutrition therapy must be adjusted to the phases of
during convalescence when inflammation resolves the disease and convalescence. Significant scientific
and elevated muscle protein breakdown rates steps have been made toward achieving this goal.
decrease, particularly when combined with physical Early energy overfeeding should be avoided,
activity [43]. Several studies have shown poor feed- although precise targets are lacking. Indirect calo-
ing performance among post-ICU patients (50–70% rimetry can guide energy targets after the initial
&
of energy and protein adequacy) [1,44 ], highlight- phase. Individualized protein dosing warrants
ing the need for specific interventions. Inadequate assessment of the LBM with BIA or ultrasound.
intake in the post-ICU phase is multifactorial There is more doubt about whether high protein
&
[44 ,45]. Several factors of poor feeding intake are intake improves clinical endpoints. However, it may
summarized in Fig. 1. mitigate muscle mass loss. Protein absorption in
In the PROSPECT-I study, Slingerland-Boot et al. critical illness is normal, however, severe skeletal
&
[46 ] showed that removal of the nasogastric tube muscle anabolic resistance may limit the effects of

FIGURE 1. Overview of multifactorial causes contributing to inadequate post-ICU nutritional intake. Created with biorender.
com. License ARH van Zanten: agreement number: UI24KC5DCW. ICU, intensive care unit.

1070-5295 Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. www.co-criticalcare.com 105
Gastrointestinal system

11. Chapple S. Stable isotope approaches to study muscle mass outcomes in

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