|To guzzle BCAAs all day or not - is that still a question or is the answer settled with the publication of two recent studies?|
One of the previously mentioned issues with BCAAs are their putative ill effects on neurotransmitter levels in the brain - effects that had only been observed in rodents, though. Now, a recent study in pigs, who are a much better model of human metabolism (even much better than most apes | Miller. 1987), is fueling the concerns about the pro-depression effects of high dose leucine supplementation.
The corresponding study (Wessels. 2016), which happens to have been sponsored by the BCAA producer Ajinomoto (quite ironic, isn't it?), sought to elucidate the response of high leucine diets on the activity of the BCAA metabolizing enzyme branched-chain keto acid dehydrogenase complex (BCKDH) and subsequent changes in the concentrations of free amino acids and amino acid derivates in several tissues, including the brain.
|Figure 1: Brian tryptophan and serotonin levels in response to diets containing normal or two- (white) and four-fold (grey bar) elevated amounts of leucine (Wessels. 2016).|
|In vivo comparison of the central action of isoleucine, valine, and leucine on glucose kinetics during pancreatic insulin clamps (Arrieta-Cruz. 2016).|
|Figure 2: BCAA content of the standard (SLD), high BCAA (HVLID) and high leucine (HLD) diets (Holecek. 2016).|
|Figure 3: Fractional rate of protein synthesis. Means ± SE, p < 0.05. *compared to the corresponding control (SLD or SLD + S); # compared to the corresponding fed group; † HLD (HLD + S) group vs. HVLID (HVLID + S) group (Holecek. 2016).|
"[...] explain the discrepancy between the protein anabolic effects of BCAA or leucine on muscles that were reported under in vitro conditions and/or shortly after BCAA intake and their reduced or lack of effects following chronic administration" (Holecek. 2016).With the present study being conducted in healthy rodents without any of the condition that lead to muscle wasting (e.g. disorders like diabetes, or natural processes like aging) and in the absence of the stimulatory effect of exercise on signalling pathways that activate protein synthesis, future studies will have to determine, whether the ill effects on protein synthesis and increases in protein breakdown are (a) even more severe in muscle-wasting disorders, the elderly, and / or during endurance exercise, and how (b) the effects are modified by resistance training.
- Arrieta-Cruz, Isabel, Ya Su, and Roger Gutiérrez-Juárez. "Suppression of Endogenous Glucose Production by Isoleucine and Valine and Impact of Diet Composition." Nutrients 8.2 (2016): 79.
- Choi S, Disilvio B, Fernstrom MH, Fernstrom JD. Oral branched-chain amino acid supplements that reduce brain serotonin during exercise in rats also lower brain catecholamines. Amino Acids. 2013 Aug 1. [Epub ahead of print]
- FAO (Food and Agriculture Organization of the United Nations. "Food and nutrition in numbers." Rome, 2014; Food and Agriculture Organization of the United Nations.
- Holeček, Milan. "The BCAA–BCKA cycle: its relation to alanine and glutamine synthesis and protein balance." Nutrition 17.1 (2001): 70.
- Holeček, Milan, et al. "Alterations in protein and amino acid metabolism in rats fed a branched-chain amino acid-or leucine-enriched diet during postprandial and postabsorptive states." Nutrition & metabolism 13.1 (2016): 1.
- Miller, E. R., and D. E. Ullrey. "The pig as a model for human nutrition." Annual review of nutrition 7.1 (1987): 361-382.
- Wessels, et al. "Branched-Chain Amino Acid Degradation and Modify Serotonin and Ketone Body Concentrations in a Pig Model." PLoS ONE 11.3 (2016).