Evidence supporting the use of: L-isoleucine
For the health condition: Muscle Tone (lack of)

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-isoleucine is one of the three branched-chain amino acids (BCAAs), along with leucine and valine, and is commonly included in dietary supplements aimed at supporting muscle health. Its use for supporting muscle tone or treating lack of muscle tone is primarily justified by scientific rationale, though direct clinical evidence is limited and not robust.

Isoleucine is considered essential, meaning it must be obtained from the diet. It plays a role in muscle protein synthesis, energy production during exercise, and muscle tissue repair. Some studies indicate that BCAAs, including isoleucine, can help reduce muscle breakdown and support muscle protein synthesis, particularly in individuals undergoing physical stress, strenuous exercise, or muscle wasting conditions. However, much of the available research focuses on BCAA mixtures rather than isoleucine alone, and the specific role of isoleucine in muscle tone (defined as the continuous partial contraction of the muscles) is less clearly established.

There is some evidence that BCAA supplementation may help preserve muscle mass and function in certain clinical populations (such as the elderly or those with muscle wasting diseases), but the effect size is generally modest. For healthy individuals, the benefits for muscle tone are less clear, and there is insufficient direct high-quality evidence that L-isoleucine supplementation alone specifically improves muscle tone. Thus, while the scientific rationale exists based on its physiological role in muscle metabolism, the overall strength of evidence specifically for muscle tone is weak to moderate (rated 2 out of 5).

More about l-isoleucine
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Other health conditions supported by l-isoleucine

Athletic and Exercise Aids
Body Building
Muscle Tone (lack of)