HMBの筋肉量増加に関する効果

今日はHMB（β-hydroxy β-methylbutyrate、BCAAのロイシンの代謝産物）の効果に関する論文を紹介します。

https://www.degruyter.com/view/j/jpem.2010.23.7/jpem.2010.23.7.641/jpem.2010.23.7.641.xml

Shawn Portal, et al: Effect of HMB Supplementation on Body Composition, Fitness, Hormonal Profile and Muscle Damage Indices. Journal of Pediatric Endocrinology & Metabolism, 23, 641-650 (2010)

BCAA製剤の摂取が筋肉量増加に有効と言われていて、その中でもロイシンが最も重要と考えられています。ただ、ロイシン20gでHMB1g、HMBの推奨量が1日3gを分2-3ですので、単純計算ですとロイシン1日60gというありえない数字になります。

そこでBCAAではなくHMBを筋肉量増加のサプリメントに使用するという選択肢が出てきます。エビデンスレベルとしてはまだ十分とは言えないと思いますが、クレアチンと同等かそれ以上の効果は期待されています。

ただ、筋肉量増加を要するリハ栄養の場面で、ルーチンにクレアチン、BCAA、HMBといったサプリメントを使用する必要はないと考えます。通常の栄養管理とリハを行ってもなかなか改善が得られない場合に、オプションの1つとして考えるのはよいかもしれません。

There is a huge market for ergogenic
supplements for athletes. However, only a few
products have been proven to have ergogenic
effects and to be effective at improving muscle
strength and body composition. One such
supplement is β-hydroxy β-methylbutyrate
(HMB). Derived from the amino acid leucine
and its keto acid α-ketoisocaproate (KIC),
HMB has been well documented as an oral
ergogenic supplement commonly used by
athletes. Several studies have shown that
combining exercise training with HMB
supplementation leads to increased muscle
mass and strength, and there is some anecdotal
evidence of aerobic improvement. However,
HMB supplementation has been found to be
effective mainly for untrained individuals.
While previous reviews have emphasized three
main pathways for HMB's mode of action: 1)
enhancement of sarcolemmal integrity via
cytosolic cholesterol, 2) inhibition of protein
degradation via proteasomes, and 3) increased
protein synthesis via the mTOR pathway,
more recent studies have suggested additional
possible mechanisms for its physiological
effects. These include decreased cell apoptosis
and enhanced cell survival, increased
proliferation, differentiation and fusion via the
MAPK/ERK and PI3K/Akt pathways, and
enhanced IGF-I transcription. These are
described here, and hormonal interactions are
discussed, along with HMB dosage and safety
issues.