Strength
L-Isoleucine
L-Isoleucine is a BCAA studied in blends, with no standalone pre-workout performance evidence.
How it counts: Not part of the score
We show it on the label and count it as disclosed, but it never affects Dose, any sub-score or the grade. The basis below explains why.
- Clinical dose
- No established clinical dose
- Safety ceiling
- —
- Evidence
- weak
- Category
- Strength
Evidence summary
Research confidence: low
No reference dose. Isoleucine is one of the three branched-chain amino acids (BCAAs), and it has been studied only as part of a BCAA mix, never on its own for exercise. Muscle needs all nine essential amino acids to build protein, which complete protein supplies and BCAAs alone do not; BCAAs alone after lifting raised muscle building about half as much as whey (Jackman 2017). No study shows BCAAs taken before a workout improve that session; the 6 g of BCAAs in Pre JYM (this 1.5 g plus leucine and valine) is about what 20 g of whey protein contains (Jackman 2017).
Research sources
- Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? (Wolfe, J Int Soc Sports Nutr 2017)(opens in new window)
- Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans (Jackman et al., Front Physiol 2017)(opens in new window)
5.6 g of the three BCAAs together after resistance exercise: muscle protein synthesis 22% above placebo, about half of whey's response. GlaxoSmithKline-funded.
- International Society of Sports Nutrition Position Stand: protein and exercise (Jäger et al., J Int Soc Sports Nutr 2017)(opens in new window)
Recommends complete protein with all essential amino acids; does not recommend isoleucine on its own