Malnutrition is a common and clinically important issue in critically ill patients. It is frequently driven by heightened inflammatory responses and catabolic stress, both of which significantly elevate nutritional demands. When these needs are not adequately met, patients may face a higher risk of complications, including delayed wound healing, hospital-acquired infections, prolonged ICU stays, and reduced survival. Accelerated muscle breakdown, in particular, contributes to rapid loss of muscle mass and strength, which can further hinder recovery.¹
Current North American and European clinical guidelines recommend protein intake levels of 1.2-2.0 g/kg/day (ASPEN)² and greater than 1.3 g/kg/day (ESPEN)³ for critically ill patients. However, determining appropriate protein targets in the ICU remains complex, especially in populations with a high prevalence of overweight and obesity. Individuals with higher BMI may have a lower proportion of protein-requiring tissue relative to total body weight, and using actual body weight (ABW) alone may overestimate protein needs.⁴ Consequently, recent approaches increasingly prioritize the use of Fat-Free Mass (FFM) or Lean Body Mass (LBM) to more precisely estimate protein requirements.³,⁵
In this issue, we highlight a recent study that assessed the impact of determining energy and protein targets using ABW⁶ and directly measured FFM⁵ in ICU patients, evaluating how these individualized nutritional goals were associated with 90-day mortality.
Actual Body Weight (ABW): The patient’s measured weight using calibrated scales.
Fat-Free Mass (FFM): The portion of body weight excluding fat, measured using bioelectrical impedance analysis (BIA).
This retrospective cohort study was conducted at Gelderse Vallei Hospital in the Netherlands and included 85 ICU patients with confirmed SARS-CoV-2 infection between March 2020 and December 2021⁶. Bioelectrical Impedance Analysis (BIA) using the InBody S10® was performed within 24 hours of ICU admission and repeated every three days to monitor changes in body composition⁶. The measurements included Total Body Water (TBW), Soft Lean Mass, Extracellular Water (ECW), Intracellular Water (ICW), Fat-Free Mass (FFM), and the ECW/TBW ratio⁶.
To account for fluid overload, FFM and Soft Lean Mass values were adjusted using a standardized method. Excess ECW was estimated by comparing the patient's ECW-to-TBW ratio with a reference value of 0.380—considered normal in healthy individuals. The difference was subtracted from the measured ECW to calculate fluid excess and refine the body composition analysis⁶.
Total Body Water (TBW): Includes all water content in the body, encompassing intracellular and extracellular compartments; typically accounts for 50–70% of total body weight.
Extracellular Water (ECW): Refers to water located outside of cells, including plasma, interstitial, and transcellular fluids. It may increase with conditions such as edema.
Intracellular Water (ICW): Refers to fluid within cells, essential for maintaining cellular integrity and function.
ECW/TBW Ratio: The proportion of total body water comprised by ECW; an elevated ratio is often used to screen for fluid imbalance or overload.
In this study, individualized nutritional targets for both energy and protein were calculated using Actual Body Weight (ABW) and Fat-Free Mass (FFM). These targets were reassessed every three days starting from ICU day 4 to accommodate changes in clinical status and nutritional tolerance⁶.
Energy requirements were estimated using the WHO/FAO/UNU equations, applied to both ABW and FFM. In accordance with ESPEN guidelines, energy intake was considered sufficient if patients received at least 70% of their calculated target during ICU stay⁶.