What's the buzz around Leucine and Muscle Protein Synthesis?
Muscle protein synthesis is crucial for most athletes, and is reliant on several nutritional aspects of the post-exercise feeding; the amount of protein, the type protein, the timing of intake to maximise nutrient release into the bloodstream and uptake by muscles, and co-ingestion with carbohydrate to enhance absorption.
The amount of protein required for optimal muscle gains is currently agreed on to be ~20 grams. More is not usually better, as synthesis maxes out, and not much more will actually be used to build muscle. See more about Protein for Athletes.
The type of protein may be what's important. Proteins contain up to 20 different amino acids (AA) of which 11 are essential (EAA), these are the ones that we need to consume because the body cannot make them. After consumption, proteins get digested, broken down into AA's and released into the bloodstream. The liver takes a portion of them for use, except for the branched-chain amino acids (BCAA's), leucine, isoleucine, and valine, which are free to be used directly by the muscle. Research suggests they have individual and collective abilities to stimulate the muscle machinery; however, leucine is understood to be the queen bee of AA's, the most important one for turning on the anabolic signalling pathways to initiate Muscle Protein Synthesis.
Aside from the recent hype over leucine, some think that consumption of all of the EAA's should promote the greatest increases. This has been supported by some research in 2017 from Aguiar et al. which found that supplementing with only leucine at 3.0 g/day post-training did not improve strength gains or muscle mass after 8 weeks of strength training. Which may show that single intake is not better than whole foods that include leucine. So there is still some parts of this story still to be explored.
Research suggests that proteins with a higher level of EAA's, that are rich in leucine are more rapidly digested, resulting in greater rates of muscle hypertrophy. Foods with the full complement of EAA's are also described as having a high biological value (HBV) and are considered to be of a higher quality.
Where is leucine found?
The content of leucine in foods varies greatly, but some foods are naturally high in leucine, including meat, poultry, fish, dairy and legumes. Dairy is very effective because the whey portion of milk protein is particularly high in leucine, plus with its faster digestion rate than other proteins, it allows blood leucine levels to peak more quickly after ingestion. A pure form of whey protein, i.e. a supplemental form, in theory is more effective than whole milk protein, casein (which is the more slowly digested milk protein), and soy proteins.
Table of foods and their leucine content
|Food type||Amount containing ~2g Leucine||Protein (g)|
|Beef and seafood||120 g||25|
|Whole eggs||2 large or 3 small||19|
|Dairy milk – skim||600 ml||22|
|Soy milk||900 ml||33|
|Cheese – reduced fat||2 slices (70g)||22|
|Cottage cheese||140 g||25|
|Yoghurt – natural||350 g||20|
|Whey protein powder||18 g||16|
|Soy protein powder||25 g||22|
|Beans, lentils, Chickpeas||350 g or ¾ cup||20-23|
|Tofu||400 g or 1 ½ cups||48|
|Nuts (almonds and peanuts)||120 g or 1 cup||26|
|Rice - cooked||6 cups||26|
Some practical tips
- Dairy milk is a better option than soy proteins due to the higher leucine content per volume and the more rapid absorption rate.
- It is slightly more difficult as a vegetarian, to achieve optimal leucine content for muscle growth, but with adequate planning it is not impossible.
- Plant protein has a slightly greater 'caloric cost' to get your 20g of protein and 2 g of leucine, meaning you need to eat a greater amount of the plant protein, with a slightly higher amount of calories, to get the same amount of leucine than from a meat-based source.
- A quality choice of HBV protein is 20g of egg albumin (the white part) which contains 8g of Essential Amino Acids (EAA) will lead to maximal muscle protein synthesis, and an increase in the oxidation of amino acids
- All meats are considered HBV protein foods and are very energy efficient choices to maximise muscle stimulus.
- Choosing recovery foods can be very individual, and choosing what suits your needs and palette is optimal for recovery.
- Strategic selection of a range of food combinations at meals and snacks throughout the day will not only result in optimisation of protein intake but also contribute to achieving intake of other essential nutrient needs.
In summary, for maximal muscle gains along with your training program, in order of importance, athletes must aim for adequate protein intake, optimise the timing of intake post-exercise, aiming for 3-4 g of leucine in that protein, and finally adding some carbohydrate to the snack/meal.
- SDA factsheet: Protein and Amino Acid Supplemetation. A sports nutrition publication of Sports Dietitians Australia. July 2011.
- Phillips, S., n.d. How Much Protein Do I Need To Eat To Build Muscle?. [online] Mysportscience.com. Available at: <https://www.mysportscience.com/post/2017/10/18/how-much-protein-do-i-need-to-eat-to-build-muscle> [Accessed 3 December 2020].
- Aguiar AF, Grala AP, da Silva RA, Soares-Caldeira LF, Pacagnelli FL, Ribeiro AS, da Silva DK, de Andrade WB, Balvedi MCW. Free leucine supplementation during an 8-week resistance training program does not increase muscle mass and strength in untrained young adult subjects. Amino Acids. 2017 Jul;49(7):1255-1262. doi: 10.1007/s00726-017-2427-0. Epub 2017 Apr 25. PMID: 28444456.
- Matthew Stark, Judith Lukaszuk, Aimee Prawitz, and Amanda Salacinski (2012) Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training. J Int Soc Sports Nutr. 9 (54). Dec 14. doi: 10.1186/1550-2783-9-54
- Jäger, R., Kerksick, C.M., Campbell, B.I. et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr 14, 20 (2017). https://doi.org/10.1186/s12970-017-0177-8
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