I want to tell you about a girl called Leucine. All her amino acid friends envy her, because Leucine is not just any girl, she’s a branched chain amino acid (BCAA), the most famous of the bunch even I’d say. Over the last 2 decades, Leucine got invited to tons of parties and researchers have been all over her. The elderly especially were exhilarated about Leucine, because they couldn’t deal with other amino acids anymore as well as they once could and it was thought that Leucine could fix these sort of problems. Leucine showed amazing promise at first, especially in animal and test tube trials, but in their wild enthusiasm, many researchers forgot to design their parties correctly. They didn’t control for total protein intake or finished prematurely before they could observe Leucine’s long term effects.
Leucine. Ain’t she something?
So let’s take a calm, good look at Leucine to determine if she’s worth your money. Let’s start by examining if she’s relationship material. By the way, all of the information below also holds for the other BCAAs isoleucine and valine.
Adding Leucine to your Meals
You can’t determine if a girl is relationship material by only looking at her for a couple hours. You want to know what having her for weeks will do to you.
Katsanos et al. (2006) found that Leucine consumption increased net protein synthesis, but consuming more than ~3g per meal had no further effect. Other research suggests the ceiling effect occurs at doses as low as 1.8g (Glynn et al. 2010). You can only handle so much Leucine. Since much larger amounts of Leucine are present in meals composed of quality protein sources in bodybuilder amounts, this suggests there is no benefit to ‘spiking’ your meals with Leucine. If you consume over 20g of protein from pretty much any sort of meat, poultry, fish, protein supplement or dairy source, you already have all the Leucine your body can handle and that doesn’t even include other good sources of Leucine, such as nuts and beans. Indeed, adding several grams of Leucine to your meals for a period of weeks has been found to have no effect on muscle gain or fat loss in the untrained, the elderly or competitive canooists (Balage & Dardevet, 2010; Björkman et al. 2011; Crowe et al. 2006; Leenders et al. 2011; Verhoeven et al. 2009). In a study comparing several cutting diet groups of elite wrestlers, BCAA supplementation on top of a sufficient protein intake had no effect on muscle retention, subcutaneous fat loss, aerobic performance, anaerobic performance or strength (Mourier et al. 1997).
Conclusion: Adding Leucine to your meals does nothing for your body composition. The only thing that will increase by having her are your bills.
Okay, so Leucine is not relationship material, but what about having her as a friend with benefits?
Knowing that adding Leucine to meals does not further increase net protein synthesis, it shouldn’t be surprising that Leucine is also of no use post-workout. It very much looks like its of use, because muscle anabolic signaling increases and the speed of protein metabolism changes, but in the end the amount of muscle built is the same (Glynn et al. 2010; Koopman et al. 2008). In this respect, Leucine is exemplary of the limitations of studies that only look at indirect measures of changes in body composition or only look at the short term. You often hear fancy theories of human physiology and of how something should work, but in the end it often just doesn’t.
Conclusion: Post-workout meals are just like other meals. Leucine doesn’t increase their anabolism.
Leucine’s Overall Rating
Save your money, guys. This chick is just a tease. Just focus on consuming sufficient amounts of whole, quality protein sources.