ASC36182
Summary of supporting
evidence
The evidence for BCAA/leucine supplementation supporting endurance performance is equivocal.
4
A recent study
5
suggests that 20 g of BCAA ingested 1hr prior to a ramp test on a treadmill can delay fatigue. However, like much of
the BCAA literature around endurance performance/fatigue there are significant flaws in the research. In the case of
5
the placebo is not matched for calories. A thorough analysis of the most recent research on BCAA and endurance
performance is needed to determine their efficacy for promoting performance. There is a great deal of heterogeneity
in the literature around supplementation protocols and dosing strategies and so firm recommendations on this are
difficult. There is an argument however, that because BCAAs become significant substrates during prolonged exercise
that supplementing may prevent muscle damage/breakdown, but there is little evidence to support this notion.
For instance, 20 g of BCAA supplemented before and during a 100 km race (3 g 1hr before followed by 17 g throughout a
100 km race) did not affect performance or markers of muscle damage.
6
There is building evidence for BCAA supplementation to augment the response to damaging exercise. A meta-analysis
of the literature from 2007-2013 suggests that BCAA supplementation may significantly reduce the severity of delayed
onset muscle soreness following damaging exercise when compared to placebo treatments.
7
Additionally, a systematic
literature review carried out on research published up to August 2017 suggests that there may be a modest benefit
of BCAA supplementation for markers of muscle damage.
8
In an analysis of the dosing strategies in this systematic
review
8
it is suggested that a daily intake greater than 200 mg
•
kg
•
day-1 (~16 g) for at least 7 days prior to the damaging
exercise may alleviate some of the impacts of muscle damage on muscle performance (force decrement, plasma
CK). However, it should be noted that the placebo in all the included trials is devoid of any protein. So, it remains to be
seen if BCAA supplementation would be better/worse than intact protein for this outcome measure. Furthermore, the
systematic review suggests efficacy of BCAA supplementation only if the damage is low-moderate.
Because BCAA/leucine are critical for signalling to increase muscle protein synthesis
3
, it has long been thought that
BCAA/leucine supplementation may enhance muscle protein synthesis and therefore growth in response to nutrition/
exercise. However, the case for supplementing BCAA/leucine in isolation seems to be weak at best. For instance, when
5.6 g (equivalent content in 20 g of Whey) of BCAA were supplemented following a session of resistance exercise the
resulting increase in muscle protein synthesis was only 22%.
8
With intact protein we would expect this stimulatory
response on muscle protein synthesis to be at least double that. So, whilst BCAAs, when taken in isolation following
resistance exercise, can stimulate muscle protein synthesis they probably should not be recommended over whole
foods containing sufficient high-quality protein. However, there may be a case for utilising BCAA/leucine to “top up”
the anabolic potential of sub-optimal meals. The leucine content of a meal seems to be the key driver of the anabolic
response (muscle protein synthesis) to that meal. Approximately 2.5 g of leucine per meal (equivalent to ~20 g of
whey protein) seems to be sufficient to maximise muscle protein synthesis.
3
Furthermore, when a suboptimal dose of
whey protein (6.25 g whey, 0.75 g of leucine) in a mixed macronutrient beverage is “topped up” with leucine to contain
3 g of leucine, it produces a similar muscle protein synthesis response in the recovery from resistance exercise
as 25 g of whey protein (3g of leucine).
9
These data suggest that leucine could be used to enhance the anabolic
potential of certain meals that may not, on their own, maximise muscle protein synthesis. This could take the form of
supplementing sub-optimal meals (plant-based meals, meals with less than 20-30 g of high-quality protein) with up to
3 g of additional leucine. However, we do not know if this strategy would support muscle growth in the long term.
Limitations to current
science
Endurance performance: The evidence on the role of BCAA/leucine in supporting endurance performance or
preventing damage from long duration activity is very heterogeneous and equivocal. From the literature so far,
a clear dosing strategy cannot reliably be suggested especially considering that the placebo is often not optimal
for assessing outcomes. There is probably room in the literature for a systematic review/meta-analysis to address
this aspect of BCAA/Leucine supplementation.
Muscle damage recovery: The evidence for BCAA supplementation in reducing the severity of symptoms following
muscle damage protocols (drop jumps, repeated eccentric contractions) is building. But the benefits appear to be
marginal and given that the placebo is often simply a calorically matched product devoid of protein it would be hard
to argue for the supplementation protocol to be implemented in place of a sound diet with sufficient high quality
protein. Furthermore, the supplementation protocols that seem to be effective (when compared against placebos
containing no protein) are likely impractical given the large daily doses required (16-20 g).
Muscle anabolism: Where intact and high-quality protein can be consumed in sufficient quantities to maximise
muscle anabolism there appears to be little-no need to supplement with BCAA/Leucine. However, where a meal is
going to be sub-optimal for maximising muscle anabolism (plant based protein or less than 20-30 g of high quality
protein) then there may be a benefit to supplementing that meal with leucine up to a total of 2.5-3 g of leucine.
It should be noted that the “benefit” in this instance is purely for muscle protein synthesis and there is not yet firm
evidence of this kind of dosing strategy augmenting other outcomes such as muscle growth, strength, or recovery
in athletic populations.
Final consensus While there is some evidence supporting the claims that BCAA/leucine supplementation favourably influences
skeletal muscle protein metabolism, efficacy is significantly less than acute ingestion of high biological value
proteins. As such, these more efficacious interventions should be prioritised over BCAA/leucine. The fortification
of lower biological value proteins with additional BCAA/leucine to optimise muscle anabolism is recognised and
discussed in a separate fact sheet on isolated protein supplements.