BCAAs Mess W/ Vegan Glucose Management, Human Study Says - Do You Have to Stay Away From BCAAs, Now?

Are vegan athletes who supplement their low BCAA baseline diet with amino acid powders making an unhealthy mistake? At first sight a recent study from Poland suggests just that. Upon closer scrutiny, however, the practical relevance of the results appear less and less convincing.

It seems (and I have to admit that I fell for that logic, too) only logical that vegans, unlike omnivores and lactovegetarians run the risk of not getting enough BCAAs from their diet. After all, their diets allow the neither the consumption of dairy nor many of the other wonderful high BCAA protein sources.

Against that background, I would venture the guess that many vegan athletes spike their diets with copious amounts of the ubiquitous BCAA supplements, supplement vendors all around the globe are pushing on unsuspecting customers who have no clue that a new study claims that these supplements may ruin one of the often-heard benefits of vegan diets: improved glucose management and reduced diabetes risk (eg. -62% in Tonstad et al. 2013).
Based on the observation that BCAAs will reduce the glucose clearance rates in healthy human beings, in some (Tremblay 2005 | glucose uptake ↓ by 33%; Robinson 2015 | glucose uptake ↓ by 40% and 23% at low and high insulin levels, respectively), but not all (Everman 2015) pertinent studies and in view of the fact that

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"[d]ata on the effect of a chronic supplementation with BCAA in humans are still limited making it impossible to clarify whether increased dietary BCAA themselves are sufficient to trigger IR-related diseases or whether the perturbations in BCAA levels only reflect an already developed insulin resistant state [here, the authors refer to the observation that people with metabolic syndrome have, across the board, significantly elevated BCAA levels in the blood]" (Gojda. 2017)

the authors speculated that supplementing healthy subjects with 20g of BCAAs (female subjects received only 15g to make up for their lower body weight) and comparing the results of vegan (=low BCAA intake) and omnivore (=high BCAA intake) subjects would yield valuable insights into the 'true' effects of BCAAs on human glucose metabolism.
Now, while I cannot tell in how far a single 12-week study can do that, i.e. contribute valuable insights into the 'true' effects of BCAAs on human glucose metabolism, I can tell you that the results Gojda et al. present in the European Journal of Clinical Nutrition will make at least the vegans in the SuppVersity audience sit up and question their use of BCAA supplements... at least for as long as they didn't read the rest of the article ;-)

Figure 1: At first sight, the changes in the subjects' basal glucose levels and their ability to clear glucose during the hyperinsulinemic euglycemic clamp test clearly suggest that 20g/15g/day BCAAs are bad for vegans (Gojda 2017).

It stands out of question, a -28% decrease in glucose clearance during the scientists' two-hour hyperinsulinemic euglycemic clamp test is quite a significant negative effect (the effect size, here, is d = 0.99; anything >0.8 is considered a "large" effect size). Before you freak out, however, it must be said that the metabolic rate of glucose clearance per unit of insulin, which is what I would consider a much better measure of insulin sensitivity, was decreased by a statistically highly non-significant, practically (check out the standard deviation in Figure 2) irrelevant 3%, only (addendum: I calculated the effect size, which is d = 0.08 and would thus confirm the lack of practical relevance of this finding, after all, anything < 0.2 is already considered a "small" effect size - 0.08 is thus quasi no effect).

Figure 2: Unlike the absolute glucose infusion rates during the hyperinsulinemic euglycemic clamp, the rates per unit of insulin were not affected by 3 months on 20/15g of BCAAs per day (Gojda 2017).

Nevertheless, the scientists are still confident to conclude that "[a] chronic increase in BCAA intake led to a decrease of IS only in vegans" (Gojda 2017) - and that despite the fact that they did not observe the typical increases in serum BCAAs seen in obese / metabolically diseased subjects during the supplementation period (only the levels of leucine increased from the 20g of BCAAs that contained leucine, valine, and isoleucine at a ratio of 4:1:1) and admit that previous studies in metabolically deranged people show "an improvement of glucose uptake after a long term high-BCAA protein supplementation" (Gojda 2017).

Obviously, the last mentioned real-world (i.e. meals vs. insulin clamp + glucose infusion as in the study at hand) effects may obviously be a mere result of an increased release of insulin in the otherwise insulin resistant subjects when they were fed cod and whey protein, the "high-BCAA protein sources" in Ouellet, et al. (2007) and Jakubowicz, et al. (2013), the two studies Godja et al. are referring to in the previously cited statement. With nothing but eventually elusive evidence from a single lab test with conditions that hardly resemble our everyday dietary glucose exposure, I would still be hesitant to jump on the 'BCAAs mess with your glucose metabolism'-train - and that's despite the fact that I have been very critical in previous articles about BCAA supplementation.
References:

• Everman, Sarah, et al. "Effects of acute exposure to increased plasma branched-chain amino acid concentrations on insulin-mediated plasma glucose turnover in healthy young subjects." PloS one 10.3 (2015): e0120049.
• Gojda, J., et al. "Chronic dietary exposure to branched chain amino acids impairs glucose disposal in vegans but not in omnivores." European Journal of Clinical Nutrition (2017).
• Jakubowicz, Daniela, et al. "Incretin, insulinotropic and glucose-lowering effects of whey protein pre-load in type 2 diabetes: a randomised clinical trial." Diabetologia 57.9 (2014): 1807-1811.
• Newgard, Christopher B. "Interplay between lipids and branched-chain amino acids in development of insulin resistance." Cell metabolism 15.5 (2012): 606-614.
• Robinson, Matthew M., et al. "High insulin combined with essential amino acids stimulates skeletal muscle mitochondrial protein synthesis while decreasing insulin sensitivity in healthy humans." The Journal of Clinical Endocrinology & Metabolism 99.12 (2014): E2574-E2583.
• Tonstad, S., et al. "Vegetarian diets and incidence of diabetes in the Adventist Health Study-2." Nutrition, Metabolism and Cardiovascular Diseases 23.4 (2013): 292-299.
• Tremblay, Frédéric, et al. "Overactivation of S6 kinase 1 as a cause of human insulin resistance during increased amino acid availability." Diabetes 54.9 (2005): 2674-2684.
• Ouellet, Véronique, et al. "Dietary cod protein improves insulin sensitivity in insulin-resistant men and women." Diabetes Care 30.11 (2007): 2816-2821.