HMB Supplement Study: Immune Response in ICU Patients

When a patient is admitted to the intensive care unit, their body enters a state of profound metabolic stress — one characterized by rapid muscle breakdown, dysregulated immune signaling, and a collapse of normal protein synthesis. Finding nutritional interventions that can meaningfully interrupt this cascade has been a long-standing challenge in critical care medicine. Now, a 2026 post-hoc analysis published in Clinical Nutrition offers new insights into how beta-hydroxy-beta-methylbutyrate (HMB) — a naturally occurring metabolite of the amino acid leucine — may influence both the inflammatory response and intracellular protein metabolism in critically ill patients (Berger MM, Viana MV, Engelen MPKJ, et al., 2026).

What This Study Found

This secondary post-hoc analysis drew on data from a previously published randomized controlled trial (ClinicalTrials.gov identifier: NCT03628365), in which critically ill ICU patients received either 3 grams of HMB per day or a placebo for a minimum of 10 days. Study procedures were conducted in the postabsorptive state on days 4 and 15 following ICU admission. A total of 37 patients were included, with a mean age of 65 years and high illness severity scores (SAPS2: 48; APACHE II: 23), indicating a genuinely high-acuity population. Baseline characteristics did not differ meaningfully between the HMB and placebo groups.

Researchers measured a broad array of biological markers, including 37 cytokines (via Luminex multiplex assay), C-reactive protein (CRP), amino acid (AA) whole-body production rates, and plasma concentrations using stable isotope tracers. The findings were notable on several fronts.

Among the 37 cytokines measured, the majority declined by day 15 in both groups — an expected trajectory during ICU recovery. However, 12 cytokines differed significantly between the HMB and placebo groups after the intervention period, with levels being higher in the HMB group. This included 7 pro-inflammatory cytokines. Rather than suggesting harm, the researchers interpreted this pattern as potentially indicative of a more efficient or appropriately activated immune response, rather than uncontrolled systemic inflammation.

On the amino acid front, whole-body production rates and extracellular pool sizes did not differ significantly between groups by day 15. However, the intracellular pool sizes told a different story. In the HMB group, intracellular concentrations of citrulline, glutamine, HMB itself, KMV (α-keto-β-methylvaleric acid), taurine, and tau-methylhistidine were all significantly elevated compared to placebo. Notably, glutamine and HMB production increased significantly more in the HMB-supplemented group.

Additionally, the study found a significant reduction in the urea-to-creatinine ratio in the HMB group by day 15 (125 vs. 181, p = 0.002), a marker that suggests reduced whole-body protein catabolism — consistent with the parent trial's finding of decreased net protein breakdown.

Clinical Significance

The findings of this study carry several layers of clinical relevance. First, the elevation of intracellular glutamine in the HMB group is particularly meaningful. Glutamine is a conditionally essential amino acid that becomes critically depleted during severe illness and is integral to immune cell function, gut barrier integrity, and antioxidant defense. The fact that HMB supplementation appears to support intracellular glutamine synthesis — rather than simply altering plasma levels — suggests a potentially deeper metabolic mechanism at work.

Second, the cytokine findings challenge a reflexive interpretation that higher pro-inflammatory markers always indicate worse outcomes. In the context of critical illness, an insufficient immune response can be just as dangerous as an excessive one. The researchers suggest that the cytokine profile observed in the HMB group may reflect a more organized and effective immune mobilization, though they appropriately caution that this post-hoc analysis cannot establish causality and that these findings require prospective validation.

Third, the decline in the urea-to-creatinine ratio reinforces prior evidence from the parent RCT and adds biochemical support to the hypothesis that HMB may help attenuate the aggressive protein catabolism that defines critical illness. Preserving lean body mass in ICU patients is not merely an aesthetic concern — it is directly tied to recovery trajectories, ventilator weaning, physical rehabilitation, and long-term functional outcomes.

It is important to note that this was a secondary post-hoc analysis of a relatively small sample (n=37). While the isotope tracer methodology is rigorous and the findings are biologically plausible, the study's authors acknowledge the limitations of its sample size and exploratory design. Larger, prospectively designed trials are needed to confirm these observations and clarify the clinical utility of HMB supplementation in critical care settings.

Current Access and Compliance Context

HMB is commercially available as a nutritional supplement and has been studied across a range of populations, including elderly individuals experiencing sarcopenia, athletes undergoing intense training, and, more recently, critically ill patients. In the ICU context, nutritional supplementation must be carefully integrated into broader feeding protocols, often involving enteral or parenteral nutrition.

The dose used in this study — 3 grams of HMB per day — is consistent with amounts used in prior human studies and is generally considered well-tolerated. However, supplementation in critically ill populations requires clinical oversight, as metabolic demands, organ function, and drug interactions vary considerably from patient to patient. The administration of any supplement in an ICU setting should be guided by a qualified healthcare provider, ideally one with expertise in clinical nutrition and critical care.

For patients outside the ICU who are interested in HMB for muscle preservation or metabolic support — such as older adults at risk for sarcopenia or individuals recovering from surgery — the evidence base, while growing, remains an active area of research. Consulting with a knowledgeable clinician is essential before beginning any supplementation protocol.

What Patients Should Know

If you or a loved one is currently in or recovering from an ICU admission, this research is a reminder that nutritional support is not a passive element of care — it is an active therapeutic intervention. The emerging science around HMB suggests it may support the body's protein-building machinery and immune coordination during critical illness, but it is not a replacement for comprehensive medical care.

For individuals managing chronic conditions associated with muscle loss, inflammation, or metabolic dysfunction, the findings from this study add to a growing body of literature suggesting that leucine metabolites like HMB may deserve serious consideration as part of a broader, medically supervised nutritional strategy. The key phrase here is medically supervised: the biochemical effects described in this study are complex, and optimizing their benefit requires individual assessment.

Ask your healthcare provider whether HMB supplementation is appropriate for your clinical situation, what dose and formulation may be relevant, and how it might interact with any existing treatments or nutritional plans you are already following.

Conclusion

The 2026 post-hoc analysis by Berger, Viana, Engelen, and colleagues represents a meaningful step forward in understanding how HMB may exert its effects in critically ill patients — moving beyond simple outcomes to examine the intracellular and immunological mechanisms that may underlie its clinical benefit. While the study's exploratory nature warrants cautious interpretation, the findings open important avenues for further investigation into HMB as a targeted nutritional intervention in high-acuity care.

As the science of peptides and metabolite-based supplementation continues to advance, staying connected with clinicians who are current on the latest evidence is more important than ever. To find a qualified healthcare provider in your area who is knowledgeable about evidence-based peptide and nutritional therapies, visit peptideassociation.org/find-a-doctor.

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Medical Disclaimer: This article is intended for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. The findings discussed are based on a specific clinical research study and should not be interpreted as definitive clinical guidance. Always consult a qualified healthcare professional before making any changes to your nutritional, supplement, or treatment regimen. Individual health circumstances vary, and only a licensed provider can assess what is appropriate for your specific situation.

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AMA Citation: Berger MM, Viana MV, Engelen MPKJ, et al. Does β-hydroxy-β-methylbutyrate (HMB) have an anti-inflammatory impact in critically ill patients? A secondary post hoc analysis of an RCT. Clin Nutr. 2026;106690. doi:10.1016/j.clnu.2026.106690. PMID: 42202485.