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HMB and leucine supplementation during critical illness and recovery.

PURPOSE OF REVIEW
Skeletal muscle wasting is a serious consequence of critical illness, which may impact on long term physical and functional disability. To date, no intervention has been proven to reduce skeletal muscle wasting. Leucine and it's metabolite β-hydroxy-β-methylbutyrate (HMB) have been proposed as interventions. This review details the mechanism of action of both leucine and HMB, discusses the most recent research for both leucine and HMB and lastly discusses considerations for future research.


RECENT FINDINGS
Only one study of leucine in critical illness has recently been published. This was a feasibility study where the physiological and muscle related outcomes were not reported to be feasible. Three studies on HMB have been reported recently with no effect seen on either muscle mass or strength. The main limitation in our understanding of the potential use of leucine or HMB on skeletal muscle wasting is the lack of mechanistic studies available in this population.


SUMMARY
Mechanistic studies should be a priority before embarking on further randomized controlled trials related to this topic.