Impact of the calcium form of β-hydroxy-β-methylbutyrate upon human skeletal muscle protein metabolism.
Level 3 - non-randomized controlled study
Single-arm pre-post metabolic tracer study in humans without a randomized control group
PubMed 29097038 · doi:10.1016/j.clnu.2017.09.024
What was done
Eight healthy young males received a primed constant infusion of 1,2 13C2 leucine and 2H5 phenylalanine to assess myofibrillar muscle protein synthesis (MPS) and arterio-venous dilution muscle protein breakdown (MPB). Measurements were taken at postabsorptive baseline and following the provision of ~3 g of oral calcium β-hydroxy-β-methylbutyrate (Ca-HMB). Muscle anabolic and catabolic signaling was assessed via immunoblotting.
What was found
Oral Ca-HMB led to a rapid (<60 min) peak in plasma HMB concentration (483.6 ± 14.2 µM, p < 0.0001). MPS increased from postabsorptive baseline (0.046 ± 0.004%/h) to post-Ca-HMB (0.072 ± 0.004%/h, p < 0.0001). MPB decreased from postabsorptive baseline (7.6 ± 1.2 µmol Phe per leg min^-1) to post-Ca-HMB (5.2 ± 0.8 µmol Phe per leg min^-1, p < 0.01). Phosphorylation of mTORC1 substrates (p70S6K1 and RPS6) increased, with no changes detected in measured MPB signaling targets.
Why it matters
This study demonstrates that oral calcium HMB acutely stimulates muscle protein synthesis and suppresses muscle protein breakdown via mTORC1 signaling, showing biological efficacy comparable to historical data for the free-acid formulation.
Limits
The sample size was very small (n = 8) and restricted to healthy young men. The trial was single-arm and uncontrolled without a placebo group or a direct within-study crossover comparison to free-acid HMB. Only acute metabolic responses to a single dose were assessed.
Cited by
- supports Calcium beta-hydroxy-beta-methylbutyrate (HMB) supplementation supports muscle recovery and attenuates muscle protein breakdown.