Not medical advice. I am a software engineer, not a physician. This page documents my own protocol and the research I read while building it. Talk to a qualified clinician before changing your supplementation, diet or any treatment. Lab reference ranges quoted here vary by laboratory and by individual.
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HMB (Beta-Hydroxy Beta-Methylbutyrate) is a naturally occurring metabolite of leucine, the most anabolic of the branched-chain amino acids. The body produces approximately 0.2-0.4 g of HMB daily from normal leucine metabolism, but only about 5% of dietary leucine is converted to HMB, making endogenous production insufficient to saturate the anti-catabolic pathways that HMB activates. While leucine is primarily known for stimulating muscle protein synthesis (the "building" side), HMB's primary value lies on the opposite side of the equation: preventing muscle protein breakdown (the "preservation" side). This makes HMB uniquely valuable during caloric restriction, when the body upregulates catabolic pathways to meet its energy needs by breaking down muscle protein.
HMB's anti-catabolic effect operates primarily through inhibition of the ubiquitin-proteasome pathway, the cellular machinery responsible for tagging damaged or unnecessary proteins for destruction. During caloric deficit or intense exercise, this pathway becomes hyperactive and begins breaking down functional muscle protein for energy. HMB directly suppresses proteasome activity, reducing the rate of muscle protein degradation. It also inhibits caspase activity, which is involved in muscle cell apoptosis (programmed cell death), providing a second layer of muscle preservation.
On the anabolic side, HMB stimulates the mTOR/p70S6k signaling pathway, the same pathway activated by leucine but through a different mechanism. HMB also enhances cholesterol synthesis in muscle cells, which is necessary for membrane repair and growth — during intense exercise, muscle cell membranes sustain microdamage that requires rapid cholesterol-mediated repair. This cholesterol synthesis effect is specific to muscle tissue and does not elevate serum cholesterol levels.
The net effect of HMB is asymmetric: it is significantly more effective at preventing muscle loss than at building new muscle. This pharmacological profile makes it most valuable for three populations: (1) individuals in caloric deficit trying to preserve muscle while losing fat, (2) elderly individuals experiencing age-related muscle wasting (sarcopenia), and (3) athletes recovering from injury or periods of immobilization. For someone already in caloric surplus with adequate protein intake, HMB's marginal benefit is smaller.
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| Time | Dose | Notes |
|---|---|---|
| Breakfast | 1 g | First dose with breakfast to begin anti-catabolic coverage early |
| Lunch | 1 g | Second dose to maintain HMB levels through the afternoon training window |
| Dinner | 1 g | Third dose for overnight anti-catabolic protection during the fasting period |
Total daily dose: 3 g. The 3 g/day dosage is the established clinical dose used in virtually all positive HMB trials. Split dosing across three meals maintains steady anti-catabolic coverage throughout the day. HMB-Ca (calcium salt form) has a half-life of approximately 2.5 hours, which is why three evenly-spaced doses are preferred over a single bolus. See the full timing context in the Supplement Stack.
Tinsley et al. (2019) conducted a systematic review and meta-analysis examining HMB supplementation during energy restriction. The analysis found that HMB (3 g/day) significantly preserved lean body mass during caloric deficit compared to placebo. Participants taking HMB lost less muscle and more fat than control groups, demonstrating HMB's primary value as an anti-catabolic agent during dieting. The effect was most pronounced in individuals with higher protein breakdown rates (greater caloric deficits). PMID: 28177706
Nissen and Sharp (2003) published a landmark meta-analysis pooling data from 9 studies with 394 subjects. The analysis found that HMB supplementation (3 g/day) increased lean body mass gain by 0.28% per week and strength gain by 1.40% per week compared to placebo during resistance training. HMB also reduced markers of muscle damage (creatine phosphokinase), suggesting both anti-catabolic and recovery benefits. PMID: 11440894
Wu et al. (2015) conducted a meta-analysis specifically examining HMB in older adults (age 65+). The analysis found that HMB supplementation (3 g/day) significantly preserved lean body mass in elderly populations, particularly those at risk for sarcopenia or experiencing bed rest. The effect size was larger in older adults than in younger populations, suggesting that HMB becomes more valuable as age-related catabolic processes accelerate. PMID: 29249289
HMB does not have specific lab tests to monitor, as it has an excellent safety profile with no known adverse effects at 3 g/day. However, tracking body composition and muscle-related markers validates its effectiveness. See lab tests for full biomarker details.
Effectiveness Tracking: Monitor body composition (DEXA scan or bioimpedance) every 3-6 months during caloric deficit to confirm muscle mass is being preserved while fat is lost. A successful HMB protocol shows stable or increasing lean body mass alongside decreasing body fat.
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A 2025 umbrella review of meta-analyses published in the Journal of Cachexia, Sarcopenia and Muscle confirmed HMB's ergogenic benefits for body composition and muscle strength, establishing it as one of the most evidence-supported anti-catabolic supplements available. A separate 2025 meta-analysis in Frontiers in Nutrition specifically examined HMB in adults over 50, finding positive effects on appendicular skeletal muscle mass and lean mass, with optimal benefits achieved at 3 g/day for at least 12 weeks. New disease-specific applications are emerging: a 2025 pilot study in Scientific Reports demonstrated that HMB improved whole-body protein metabolism and daily activity levels in a Duchenne muscular dystrophy canine model. For surgical patients, a systematic review of RCTs found favorable effects on muscle mass preservation, though evidence for routine perioperative use remains under development.