In order to get the most from your time in the weights room, you might want to start thinking about adding more Branched-chain Amino Acids (BCAAs) and Leucine to your diet. But what are they? What will they do for you? Do you even need them? Here’s everything you need to know.
Protein is a macronutrient – nutrients that are required in larger amounts – and plays numerous key roles in the body, one of which is in maintaining, repairing and building muscle.
Protein molecules vary in structure and length and are made up of ‘units’ known as amino acids. Several hundred different amino acids have been identified in nature, 20 of which are particularly important because they help protein synthesis.
Nine of these are essential for humans to consume in our diets as they can’t be created from other amino acids, and these are known as Essential Amino Acids (EAAs). Three of these are categorised as Branched-chain Amino Acids – so-called because of their structure – and these are leucine, isoleucine and valine.
Different protein-rich foods vary in their protein quality, and you can read more about this in our Guide to Protein Quality, Digestion and Absorption.
Protein synthesis is the mechanism by which certain key structures in the body, including muscle tissue, skin, enzymes, some hormones, neurotransmitters, and immune factors (to name but a few) are formed from amino acids.
Without consuming a good amount of protein in the diet, which includes sufficient amounts of each of the nine EAAs, other less-essential tissues are broken down in order to prioritise what the body needs to keep us alive.
What does protein malnutrition look like? Signs and symptoms may include fatigue – especially during physical activity – muscle wasting, and a compromised immune system.
BCAAs are present in high concentrations in muscle tissue, which helps explain their popularity with bodybuilders and strength athletes. BCAAs have other key roles – for example, isoleucine is involved in increasing glucose uptake into cells, and this process doesn’t involve the other BCAAs, so it may help to promote energy during exercise.
However, the most important function of BCAAs – in particular leucine, which is more potent than isoleucine and valine – is their role in controlling the onset of protein synthesis.
BCAAs stimulate the activity of an enzyme called mTOR[2-5]. mTOR (which stands for “mechanistic, or mammalian, target of rapamycin”) is an enzyme that is the key regulator of protein synthesis, as well as other processes like cell growth and breakdown.*
mTOR is a very important enzyme as it regulates all metabolic processes in most animal tissues, including muscle, and poor functioning of it is linked to diabetes, obesity, depression and certain cancers[8-10].
Here we’re more interested in mTOR’s role in regulating protein synthesis for muscle growth and recovery after exercise. If mTOR is inactive for long periods, this will result in muscle wasting, and this is part of the reason for the loss of muscle mass and tiredness in people with advanced wasting diseases – cancer cachexia, for example.
To put it simply, think of mTOR as a switch, which when turned to ‘on’ will initiate protein synthesis, and leucine is the pressure required in order to press the switch.
When the level of leucine is high enough, the ‘switch’ is turned ‘on’ and muscle tissue can be repaired. When leucine levels go down, the ‘switch’ is released and protein synthesis turns ‘off’.
Supplementary leucine may enhance strength and performance[11-14], and resistance exercise may further promote its effects[15-16]. However, the effect is related to how much leucine is present in a meal containing at least 20g of protein.
As part of a protein meal, a total BCAA level of at least 4.5g of which at least 2.2g is leucine, has been shown to be sufficient to stimulate protein synthesis. This could be in the form of a supplement, or by consuming a high-quality protein meal or snack.
|Huel Product||Serving Size||Protein||Calories||BCAAs||Leucine|
|Complete Protein (v1.0)*||29g||20.4g||105||4.8g||3.1g|
|Black Edition (v1.1)*||90g||40g||400||7.4g||3.5g|
|Hot & Savoury (v1.0)**||95g||25g||400||4.3g||2.0g|
|Ready To Drink (v1.0)*||500ml||20g||400||3.5g||1.7g|
Table showing the levels of BCAAs and leucine compared to the total protein and calories per serving:
* Vanilla flavours
** Korma flavour
*** Chocolate flavour
* For accuracy, mTOR is actually an enzyme complex of which there are two and these also involve other protein factors; for ease when referring to mTOR, we mean mTOR Complex 2.
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