If you take a hefty portion of the amino acid L-citrulline just before going to sleep at night, it might help you to maintain muscle mass even though you’re on a low-cal diet and are aiming to lose fat. At least, it might do so if you react in the same way as the rats did that researchers at the Universite Paris Descartes used for their experiments. The French researchers published their findings in Amino Acids.
If you take a hefty portion of the amino acid L-citrulline just before going to sleep at night, it might help you to maintain muscle mass even though you’re on a low-cal diet and are aiming to lose fat. At least, it might do so if you react in the same way as the rats did that researchers at the Universite Paris Descartes used for their experiments. The French researchers published their findings in Amino Acids.
Millions of people spend more time dieting than they do eating ordinarily. That is of itself not a bad thing, if you consider how many people are overweight. But there’s one big disadvantage to permanent dieting: if you don’t do weight training at the same time or make sure that you consume relatively large amounts of protein, you’re likely to lose muscle mass. And this not only can undermine the success of your weight loss attempts – muscles just happen to be big calorie burners – but in the long term may also increase the risk of weak muscles in old age.
The researchers suspected that supplementation with L-citrulline or L-leucine may help relieve this situation. According to animal tests, both amino acids can help the anabolic mechanism in muscle cells to work a littler harder. [Amino Acids. 2012 Sep;43(3):1171-8.]
The researchers put female rats on a two-week diet, during which they were given sixty percent of the food they’d eat if they were allowed to eat as much as they wanted. The table below shows this reduced the fat mass by a statistically significant amount [Control restricted] when compared with the rats that ate as much as they wanted [Basal control].
However, if the rats were given a dose of 1 g L-citrulline per kg bodyweight orally [R-CIT 1] before going to sleep, they retained slightly more muscle mass. The effect was not statistically significant, though. Administration of a similar amount of L-leucine – this was mixed with the rats’ feed – had less effect on the muscle mass [R-LEU].
The figure above shows what the researchers found when they measured the amount of contracting protein in the muscle cells of the rats. The reduced calorie intake meant that less muscle tissue was built up. Leucine supplementation was not able to prevent this; supplementation with L-citrulline did do so.
The researchers also looked at the effect of the combination of L-leucine and L-citrulline [LEU-CIT]. The addition of L-leucine counteracted the positive effect of L-citrulline, the researchers discovered. They don’t understand how this happens.
The researchers suspect that leucine stimulates muscle growth if the body is also given high amounts of amino acids and other nutrients. During calorie restriction or a period of fasting, L-citrulline is a better muscle growth enhancer than L-leucine, however.
Effect of citrulline on muscle functions during moderate dietary restriction in healthy adult rats.
Ventura G, Noirez P, Breuillé D, Godin JP, Pinaud S, Cleroux M, Choisy C, Le Plénier S, Bastic V, Neveux N, Cynober L, Moinard C.
Source
Laboratoire de Biologie de la Nutrition EA4466, Faculté de Pharmacie, Paris Sorbonne Cité, Université Paris Descartes, 4 avenue de l’observatoire, 75270, Paris Cedex 06, France, gabrielle.ventura@nutrition-paris5.org.
Abstract
Low calorie diets are designed to reduce body weight and fat mass, but they also lead to a detrimental loss of lean body mass, which is an important problem for overweight people trying to lose weight. In this context, a specific dietary intervention that preserves muscle mass in people following a slimming regime would be of great benefit. Leucine (LEU) and Citrulline (CIT) are known to stimulate muscle protein synthesis (MPS) in post-prandial and post-absorptive state, respectively. This makes them interesting bioactive components to test in the context of dietary restriction. We tested the concept of combining LEU and CIT in adult female rats. We postulated that the sequential administration of LEU (mixed in chow) and CIT (given in drinking water before a rest period) could be beneficial for preservation of muscle function during food restriction. Sixty female rats (22 weeks old) were randomized into six groups: one group fed ad libitum with a standard diet (C) and five food-restricted groups (60 % of spontaneous intake for 2 weeks) receiving a standard diet (R group), a CIT-supplemented diet (0.2 or 1 g/kg/day, CIT0.2 group and CIT1 group, respectively), a LEU-supplemented diet (1.0 g/kg/day) or a CIT + LEU-supplemented diet (CIT + LEU 1.0 g/kg/day each). At the end of the experiment, body composition, muscle contractile properties and muscle protein synthesis (MPS) rate were studied in the tibialis anterior muscle. Dietary restriction tended to decrease MPS (R: 2.5 ± 0.2 vs. C: 3.4 ± 0.4 %/day, p = 0.06) and decrease muscle strength (R: 3,045 ± 663 vs. C: 5,650 ± 661 A.U., p = 0.03). Only CIT administration (1 g/kg) was able to restore MPS (CIT1: 3.4 ± 0.3 vs. R: 2.5 ± 0.2 %/day, p = 0.05) and increase muscle maximum tetanic force (CIT1: 441 ± 15 vs. R: 392 ± 22 g, p = 0.05) and muscle strength (CIT1: 4,259 ± 478 vs. R: 3,045 ± 663 A.U., p = 0.05). LEU had no effect and CIT + LEU supplementation had few effects, limited to adipose mass and fatigue force. The results of this study highlight the ability of CIT alone to preserve muscle function during dietary restriction. Surprisingly, LEU antagonized some effects of CIT. The mechanisms involved in this antagonistic effect warrant further study.
PMID: 23913268 [PubMed – as supplied by publisher]
Source: http://www.ncbi.nlm.nih.gov/pubmed/23913268
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