L-leucine is one of the essential amino acids, which means that the human organism cannot produce this amino acid itself. L-leucine must be supplied through the diet. It is found in all protein-containing foods (both animal and vegetable).
High levels of leucine are found, for example, in rice, walnuts, dried peas, salmon, beef and chicken (see table below). The required daily dose is estimates of approximately 10-50 mg/kg body weight.
Due to its specific molecular structure, leucine belongs to the so-called branch-chained amino acids (BCAAs). Valine and isoleucine also belong to this group.
A special feature of BCAAs is that, unlike other amino acids, their metabolism is only slightly converted in the liver, but mainly in other tissues, such as muscle tissue. Leucine plays an important role in the energy balance in muscle tissue.
Leucine content in selected foods (nutritional values per 100g)
Total protein in g
Leucine in g
Chicken breast fillet, raw
Rice Protein Isolate Protein Powder
Pea Protein Isolate
Leucine is a proteinogenic amino acid, which means that it is a component of many proteins and plays an important role in maintaining and building muscle via protein biosynthesis in muscle.
Since leucine is predominantly broken down directly in the muscle, this also inhibits the breakdown of muscle protein and correspondingly reduces the breakdown of muscle tissue. Leucine also plays a supporting role in healing processes.
A loss of muscle mass is almost impossible to prevent in the event of an injury. Immobilization of certain muscles (such as by a cast) causes muscle breakdown to be greater than muscle gain. This is also referred to as a negative nitrogen balance. The same applies, of course, to (prolonged) bed rest.
Due to the important function of leucine as an active ingredient in reducing muscle wasting, there is reason to believe that leucine can help maintain muscle mass in such cases.
English et al. got to the bottom of the matter and studied the effects of daily intake of 13g of leucine on a group of middle-aged adults. These were relegated to a week of bed rest. The intake of 13g of leucine a day had an amazing effect: it was possible to reduce the loss of lean mass and decrease the gain of body fat.
This is also an important finding for injured athletes, as increased body fat levels after injury are often a problem.
In this study of tennis players, a drop in blood leucine levels was observed after several hours of endurance exercise. From this, the logical conclusion can be drawn that the consumption and thus the demand of leucine increases during endurance loads.
Leucine also convinced canoeists with amazing results. Over a period of 6 weeks, athletes were fed leucine daily. According to the canoeists, the subjective perception of the training effort was lowered by the leucine supply: the exercises performed felt ” lighter” .
This could also be confirmed on paper. Rowing time to exhaustion was improved after the 6 weeks and an increase in upper body strength endurance could also be measured.
In other studies and investigations, the following results and positive effects of leucine were observed, among others:
6. Crowe, M.J., Weatherson, J.N., Bruce F. Bowden. (2006). Effects of dietary leucine supplementation on exercise performance. European Journal of Applied Physiology
7. English, K.L., Mettler, J.A., Ellison, J.B., et al. (2016). Leucine partially protects muscle mass and function during bed rest in middle-aged adults. The American Journal of Clinical Nutrition
8. Strüder, H.K., Hollmann, W., Duperly, J., et al. (1995). Amino acid metabolism in tennis and its possible influence on the neuroendocrine system. British Journal of Sports Medicine
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