Okay, after having searched a bit about leucine, I see why one might want to use only leucine, but I would still combine an all around amino acid complex with a lot of leucine. On anyvitamins.com, I found:
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Leucine is required for
Leucine helps with the regulation of blood-sugar levels, the growth and repair of muscle tissue (such as bones, skin and muscles), growth hormone production, wound healing as well as energy regulation. It can assist to prevent the breakdown of muscle proteins that sometimes occur after trauma or severe stress. It may also be beneficial for individuals with phenylketonuria - a condition in which the body cannot metabolize the amino acid phenylalanine
Deficiency of leucine
Deficiency of this nutrient is rare, since all protein foods contains it, but vegans and vegetarians without adequate protein sources may suffer from a deficiency. Hypoglycemia symptoms may appear if the diet is deficient and may include dizziness, fatigue, headaches, irritability etc.
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What really intrigues me is the part about blood sugar. Since I'm hypoglycemic, I wonder if supplementing with leucine may stop or reduce my symptoms. I also saw a reference to a study elsewhere that said leucine prevented muscle loss in rats so perhaps it may do the same in humans.