The Glucose Repartitioning Effects of Isoleucine: Falsely Underappreciated BCAA and Its Dipeptides Maximize GLUT-4 Expression and Ramp Up Muscular Glucose Uptake
|Still waiting for your abs to appear? Maybe you have the wrong "scientifically proven", "superior", or "modern", but unnatural ratio of BCAAs in your peri-workout nutrition - just kiddin' that alone won't be the reason, but still...|
Leucine was yesterday, isoleucine is the future - at least for lean mass gains
|You already know from previous articles that EAAs increase GLUT-4 expression - could it be that this effect was stimulated by isoleucine, alone? As a branch-chained amino acid it is after all one of the EAAs. Or is it rather a synergistic effect of various amino acids?|
To study the individual effects of various components of whey on glucose uptake, the scientists administered a mixture of glucose + whey protein hydrosolate or one of the following amino acids / dipeptides to 49 rats who had been exercised the day before and were kept in a fasted state for 15:30hr afterwards (this protocol was meant to deplete muscle and liver glycogen): L-isoleucine (ILE), L-leucine (LEU), L-leucine plus L-isoleucine (LEU+ILE), L-isoleucyl-L-leucine and (ILE-LEU), L-leucyl-L-isoleucine (LEU-ILE).
Important recent update on isoleucine: I highly suggest you read my more recent article on isoleucine, as well. It discusses the beneficial effects on blood glucose in man, but adds that an amino acid mix containing high amounts of isoleucine blunts glycogen resynthesis after the workout.After receiving these solutions, the animals (N=7 per group) were sacrificed and the effects on glucose transporter 4 (GLUT-4), p-Akt and AMPK in skeletal muscle, as well as the insulin and glucose levels in the blood and the glycogen content of liver, skeletal muscle and heart were evaluated.
|Figure 1: Skeletal muscle protein expression, insulin and glucose levels and glycogen content of muscle, liver and heart 30min after the ingestion of the glucose + whey / AA / peptide solutions (Morato. 2013)|
Where did the glucose go, dude?
|Training glycogen deplete can be regarded as an intensity technique that can increase markers of mitochondrial biogenesis by +700% (read more), not repleting your glycogen levels for days must be regarded as madness, though.|
Now you could certainly argue that the scientists would not have had to measure the glycogen content, in the first place, if they already knew it would not change. In a way, this is correct, but since we know that the rate of glucose uptake is inversely related to the glycogen levels in the muscle, measuring the actual glycogen content was necessary simply to make sure that inter-group differences in terms of the amount of glycogen that was still left in muscle, liver and heart tissue of the animals would not interfere with the study outcomes.
Amino acids, lactate dehydrogenase (LDH), creatine kinase and more
|No wonder the cup on the left is the only one that smiles. The black coffee it contains may be among the least known, but most consumed GLUT4 promoters worldwide. That's at least what a paper by Guarino et al. from 2012 suggests. And while this partly explains the reduced diabetes risk in habitual coffee drinkers, the lower incidence of CVD and cancer are brought about by the natural synergy of various nutrients in coffee (read more)|
In addition to the previously discussed parameter, Morato et al. also analyzed a whole host of additional parameters, mostly with non-significant or physiologically irrelevant results. One thing that's worth mentioning though are the higher serum levels of the (main) glyconeogenic amino acid l-alanine in the l-isoleucine group.
The scientist ascribe the latter to the competition of isoleucine and alanine for hepatic transport via the neutral amino acid transporter. The decreased uptake of alanine by liver, in turn, could have reduced hepatic (=by the liver) gluconeogenesis and thus contributed to a further reduction (or absence of an increase) in serum glucose levels. This would also explain the lower ALT levels in the isoleucine group. After all, this enzyme that's often misattributed as an indicator of liver damage is actually nothing but a marker of the transamination of alanine (hence "ALT" as in ALanine amino-Transferase), a process that is a necessary step in hepatic gluconeogenesis from alanine to pyruvate, which will subsequently be converted to glucose and released into the blood.
Bottom line: If we recap the results the main take home messages of this study are as follows: (1) Never mess with nature's wisdom *lol*; (2) the hitherto mostly overlooked #3 of the BCAAs could be a very important contributer to the nutrient and thus body recompositioning effects of branch-chained amino acids and BCAA rich protein; (3) while l-isoleucine may be king, when it comes to the non-insulin dependent increase in GLUT-4 activity and the subsequential lowering of blood glucose, the whey(-exclusive?) dipeptide l-leucyl-isoleucine with its profound effects on both Akt and insulin, is probably the more anabolic GLUT-4 stimulant.
|Having 10g of essential amino acids (EAAs) or 2030g of "high quality = high EAA" protein with each and every of your meals is one of the easiest an most reliable strategies to become and stay lean (read more). With isoleucine obviously being one of those EAAs and 25g of whey and casein having ~1.75g respectively 1.13g of this carbohydrate repartitioning amino acid in it, this could well explain part of the benefits (note: 125g of chicken breast will also yield 1.5g of isoleucine and the same amounts of beef and pork also have >1g; the same goes for 3-4 eggs or 500g of peas and 2.5kg pumpkin or 4kg of eggplant ;-)|
Whether or not there would be real world benefits of isolated l-isoleucine supplementation for people with compromised insulin sensitivity or even full-blown diabetes will have to be elucidated in future studies. In view of the fact that BCAAs have yet already been proposed as viable "treatment" (I'd rather prefer the term "management", though) strategies for type II diabetes and related diseases (e.g. Manders. 2012; Takeshita. 2012) and considering the fact that leucine alone did not have any beneficial effects on glucose management on pro-diabetic diets (Nairizi. 2009), the addition of some isoleucine to products meant to increase glucose uptake from skeletal muscle does certainly look worth investigating. Whether the outcomes will be significantly superior to those of plain whey protein hydrolysates (Sousa. 2012), on the other hand, is something I wouldn't be too certain about.
- Jentjens R, Jeukendrup A. Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Medicine. 2003; 33(2):117-144.
- Manders RJ, Little JP, Forbes SC, Candow DG. Insulinotropic and muscle protein synthetic effects of branched-chain amino acids: potential therapy for type 2 diabetes and sarcopenia. Nutrients. 2012 Nov 8;4(11):1664-78.
- Morato PN, Lollo PCB, Moura CS, Batista TM, Carneiro EM, Amaya-Farfan J. A dipeptide and an amino acid present in whey protein hydrolysate increase translocation of GLUT-4 to the plasma membrane in Wistar rats, Food Chemistry. 2013 [epub ahead of print].
- Nairizi A, She P, Vary TC, Lynch CJ. Leucine supplementation of drinking water does not alter susceptibility to diet-induced obesity in mice. J Nutr. 2009 Apr;139(4):715-9.
- Sousa GT, Lira FS, Rosa JC, de Oliveira EP, Oyama LM, Santos RV, Pimentel GD. Dietary whey protein lessens several risk factors for metabolic diseases: a review. Lipids Health Dis. 2012 Jul 10;11:67.
- Takeshita Y, Takamura T, Kita Y, Ando H, Ueda T, Kato K, Misu H, Sunagozaka H, Sakai Y, Yamashita T, Mizukoshi E, Honda M, Kaneko S. Beneficial effect of branched-chain amino acid supplementation on glycemic control in chronic hepatitis C patients with insulin resistance: implications for type 2 diabetes. Metabolism. 2012 Oct;61(10):1388-94.