HMB (Beta-Hydroxy Beta-Methylbutyrate) vs L-Tyrosine

Mechanism

HMB is a metabolite of leucine (produced endogenously at ~0.3g/day from typical leucine intake). It reduces proteolysis by inhibiting the ubiquitin-proteasome proteolytic pathway and attenuating caspase-mediated apoptosis in muscle cells. HMB also stimulates muscle protein synthesis via mTOR/p70S6K pathway activation (though less potently than leucine itself) and enhances sarcolemmal membrane integrity by serving as a precursor for de novo cholesterol synthesis in muscle cells (via HMG-CoA). The net effect is anti-catabolic rather than primarily anabolic — it prevents muscle breakdown more than it builds new muscle.

Standard Dosing

3g daily (1g 3x/day)

Timing

Split into 1g doses with meals (HMB-Ca) or 1-2g 30-60 min pre-exercise (HMB-FA for rapid absorption). Timing matters more for HMB-FA (free acid) than HMB-Ca (calcium salt).

Cycle Duration

ongoing during training periods

Side Effects

• Generally very well tolerated
• Mild GI discomfort
• Bloating

Contraindications

• Few known. Renal impairment (monitor at high doses).

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Mechanism

L-Tyrosine is the precursor amino acid for catecholamine neurotransmitter synthesis: tyrosine hydroxylase converts tyrosine to L-DOPA (rate-limiting step), which is then converted to dopamine, norepinephrine, and epinephrine. It is also the precursor for thyroid hormones (iodination of tyrosine residues on thyroglobulin produces T3/T4) and melanin (via tyrosinase). Under conditions of acute stress, catecholamine turnover increases dramatically, depleting brain tyrosine pools. Supplementation provides substrate to maintain catecholamine synthesis during stress, sleep deprivation, cold exposure, and cognitive demand.

Standard Dosing

500-2000mg daily

Timing

Morning on empty stomach (competes with other large neutral amino acids for BBB transport). 30-60 min before stressful tasks or exercise.

Cycle Duration

As needed or cycle 4-8 weeks on, 2 weeks off

Side Effects

• Headache
• GI upset
• Irritability
• Anxiety (excess catecholamines)
• Insomnia if taken late
• Heart palpitations (high doses)

Contraindications

• MAO inhibitor therapy
• Hyperthyroidism
• Melanoma (tyrosine is a melanin precursor)
• Phenylketonuria (tyrosine from phenylalanine metabolism)

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