Why Take A Leucine Supplement?
Leucine is an essential amino acid that directly influences, among other things, muscle protein synthesis (MPS). If you’ve been following this series and read the post on protein supplementation, you’ll remember that MPS is a big deal for guys as they get older. As we age, we begin losing muscle (a process known as sarcopenia). But if we’re physically active and keep our protein intake up, we can slow the process. Some studies have shown that increasing our protein intake is even more beneficial as we age. 
Because leucine assists in MPS, increasing your plasma leucine level assists in metabolizing protein and therefore building – and maintaining – muscle tissue.
Sources of Leucine
Lean meat like beef, pork or chicken is high in leucine. Dairy products, especially cheese and Greek yogurt, are generally high in leucine as well. In fact, a serving of Greek yogurt has about as much leucine as four eggs. Finally, legumes, which are also high in protein, also contain a significant amount of leucine.
You can purchase (affiliate link) a leucine supplement by itself or as a part of a BCAA (branched chain amino acid) supplement. Or, many protein powders contain some sort of added leucine / BCAA cocktail as well.
When To Take Leucine
Research has shown that leucine can have an affect both pre and post-workout. Because leucine seems to impede muscle breakdown during workouts, many folks take some kind of supplement either before or during workouts. And because leucine helps kick protein synthesis into high gear, often it can be taken with a protein supplement post-workout to make the most out of the anabolic response to your workout. (If you’re sucking down a protein shake post-workout, you may already be getting the leucine you need, because many protein powders contain added leucine.)
There has been some speculation that taking leucine before bedtime is helpful as well. But even though protein ingestion before bed has been proven to boost MPS, research seems to indicate that adding a leucine supplement at bedtime has no effect.  Why waste it?
If you’re looking to build and/or maintain muscle mass and strength after 50, you have to make the most of every opportunity to increase muscle protein synthesis. Resistance exercise kicks MPS into gear, added protein provides the raw materials, and leucine seems to provide the pathway. Add a leucine supplement to your pre or post-workout shake to build even more muscle.
 Dan J. Weinert, DC, MS*, “Nutrition and muscle protein synthesis: a descriptive review”. The Journal of the Canadian Chiropractic Association. 2009. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2732256/
 Paddon-Jones D, Short KR, Campbell WW, Volpi E, Wolfe RR. “Role of dietary protein in the sarcopenia of aging”. Am J Clin Nutr. 2008;87(5):1562S-1566S. https://www.ncbi.nlm.nih.gov/pubmed/18469288
 Joanne Marie, “A List of Leucine-Rich Foods”. Livestrong.com. 2017. https://www.livestrong.com/article/346375-a-list-of-leucine-rich-foods/
 Matthew Stark, Judith Lukaszuk, Aimee Prawitz, and Amanda Salacinski, “Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training”. J Int Soc Sports Nutr. 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3529694/
 Jorn Trommelen and Luc J. C. van Loon, “Pre-Sleep Protein Ingestion to Improve the Skeletal Muscle Adaptive Response to Exercise Training”. Nutrients. 2016. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5188418/