From Ergo Log
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.
Click here for how to calculate the human equivalent dose.
Amino Acids. 2013 Aug 3. [Epub ahead of print].