The Counterintuitive Catabolic & Pro-Diabetic Effects of Leucine Supplementation in Rodents on Corticosteroids

Not the mice from this study, but still a nice example of the effects of dexamethasone on skeletal muscle (right; Quin. 2012)

"Leucine-laced water + stress = insulin resistance" - This simple equation is the net result of a recent study by Nelo Eidy Zanchi and his colleagues from the Laboratory of Applied Nutrition and Metabolism at the School of Physical Education and Sports of the University of Sao Paulo in Brazil. Inspired by previous research which clearly indicated that leucine does not only have pro-anabolic, but also insulin sensitizing effects, Zanchi et al. speculated that the provision of adequate amounts of leucine would blunt the catabolic and pro-diabetic effects of 7 days of intraperitoneally injections of  dexamethasone, an artificial corticosteroid that's used to treat all sorts of inflammatory diseases.

Remember SuppVersity Rule of Smart Supplementation No. 2? Right. Specificity!

In order to test their hypothesis that leucine supplementation either in low doses in the drinking water or as higher dosed oral gavage would ameliorate the negative side effects of DEXA treatment, the scientists randomized groups of 10 male Wistar rats to six groups receiving either low dose or high dose leucine supplements with and without dexmethasone.

"During  the duration of the experiment, which lasted  seven  days,  DEXA (a synthetic glucocorticoid analogue that does not bind to plasma binding proteins) was given daily (at 9:00 a.m.) through intraperitoneal injection (5 mg/kg/day); control groups received  an equivalent volume of saline (0.9% NaCl). As DEXA was reported to decrease food intake, all groups were  fed the same amount of food (in terms of caloric intake) equal to the DEX group. Thus, differences among groups did not originate from different food intakes. We measured the caloric content of our standard chow (16.32 kJ/g) as well as leucine (25 kJ/g) in a calorimetric bomb (FTT Oxygen Bomb Calorimeter) in  order to avoid differences in the caloric ingestion between experimental groups and observed that the total caloric consumption was not statistically different among groups." (Zanchi. 2012)

The leucine was administered either in dosages of 0.068g/kg body weight per day (low dose) or 1.35 g/kg per day (high-dose) twice daily at 8:00  a.m. and  2:00  p.m. through gavage over seven days. And while the scientists had selected the high dose (LH) "to induce a maximal increase in muscle protein synthesis and insulin plasmatic levels", the dosage in the LL (=low leucine) group was too low to increase either muscle protein synthesis or plasma insulin levels. The third, non-supplemented control group received an NaCl (sodium) placebo, the volume of which was identical to the supplement to make sure that any possible volume-induced effects of oral gavage that could for example be induced by gastric expansion would not skew the study results.

"But leucine has been shown to be anabolic! So it must help."

Aside from the usual basal fasting glucose, insulin, tryacilglycerol (TAG) and HOMA-IR values, the scientists did also assess the motor performance of the animals by the means of two standardized strength and ambulation tests (Kennel. 1996; Anderson. 2004; Viera. 2008).

Figure 1: Effect of 7 days of low (LL) and high (LH) dose leucine supplementation with and with out dexamethasone on total body mass, soleus (slow twitch) and EDL (fast twitch) muscle mass in male Wistar rats (left; values expressed relative to non-supplemented control) and corresponding changes in mean ambulation and grip strength (right; Zanchi. 2012)

As you can see in figure 1 the supplemental leucine failed to reduce the negative side effects of dexamethasone. As far as the total body weight and the fast-twitch muscle mass (EDL) are concerned, you could even argue that the high dose treatment (DEX-LH) did even amplify the catabolic effects of the synthetic corticosteroid:

"Thus, leucine supplementation at both low and high doses did not counteract body weight loss in both food restricted (control groups) and DEXA-treated animals. Soleus muscle mass did not differ among groups. Leucine supplementation at  high doses  attenuated food  restriction-induced EDL muscle loss (CON-LH group) when compared with the CON-NS group  (p < 0.05). All DEXA-treated animals presented reduced EDL muscle mass when compared with the CON-NS group (p < 0.05), and leucine supplementation at both low and high doses of amino acid did not attenuate it." (Zanchi. 2012)

Now, you may well argue that the mere fact that the muscle weight was "statistically significant" reduced, this does not mean that these reductions would be physiologically significant and that the minimal differences between the DEX groups would not matter, anyway. If you just go by the data on the left side of figure 1, this is certainly right, if you do yet also consider the significant reductions in muscle function (figure 1, right) and the fact that all that happened within no more than 7 days, the overall result should actually remind you of the "Three Simple Rules of Smart Supplementation" - and here specifically the 2nd one: Specificity!

Figure 2: Time course of the dexamethasone-induced detoriations in fed serum glucose levels and ameliorative effect of low and high dose leucine supplementation (left) and effects of the treatment on fasting insulin levels and HOMA-IR (index of insulin resistance) at the end of the study (Zanchi. 2012)

In fact, the data in figure 2 only confirms the notion that things that you cannot define "good and bad", "black and white" and "beneficial or detrimental" without a context and the outcome you are expecting. If you are trying to keep the postprandial blood sugar in check, for example he addition of an effective (high dose) of leucine to the diet would appear to be a good idea. If, on the other hand, you are more concerned about insulin resistance, you would be better advised to use minimal amounts of leucine or simply refrain from supplementation altogether.

Figure 3: If the ingestion of bolus amounts of leucine is not helpful, lacing the water of the rodents DEXA treated rodents with leucine turned them into full-blown diabetics (Zanchi. 2012)

As these results clearly demonstrate the provision of additional leucine is not useful to counter the negative side-effects of synthetic corticosteroids. On the contrary, the negative effects on insulin resistance are apparently even augmented and the muscle function is further compromised by the purpotedly anabolic high dose leucine supplement.

And while the overall effects of the bolus administration may still be negligible, the scientists ingenious idea that the provision of similar amounts of leucine in the drinking water in a second follow-up experiment turned out to be "capable of inducing a massive diabetic state" (Zanchi. 2012; see figure 3 for the ensuing surge in fasting blood glucose levels) while decreasing the mass of the fast-twich EDL muscles even further.

Bottom line: Overall these results only confirm the simple, but often neglected truth that inductive reasoning is a futile undertaking in the realms of exercise and nutrition sciences: What is good for an athlete is rarely optimal for an obese person, the same diet that helps the obese lose weight, will make the athlete feel miserable, and lacing the drinking water of rodents on corticosteroids with the exact same amount of leucine that has had highly beneficial effects on the insulin sensitivity of diabetic rodents in previous studies (Guo. 2010) will not only fail to ameliorate the glucocorticoid-induced detoriations in blood glucose, it will even exasperate them.

That said, there may even be implications for the average pre-diabetic inhabitant of the Western hemisphere who is eating his hamburger and French fries on the parking lot of the local fast food restaurant, because he cannot make room to prepare and consume a real meal somewhere in his busy and stressful schedule. I mean, despite the fact that the aforementioned specificity principle does not allow for anything but a still to be verified hypothesis, it does at least appear not to far-fetched that this chronic endogenous stress, despite being very different from the "stress" that's induced by the administration of a synthetic corticosteroid that does not bind to serum proteins, could have similar negative modulatory effects on the purported benefits of chronic leucine supplementation ... but as I've said before, this would be something to investigate in another study. So unless you are actually taking dexamethasone for medical reasons, you are probably not at risk of developing diabetes due to a high amount of leucine in your diet.

In the unfortunate case that you are actually on synthetic corticosteroids, a previous study by the same group of scientists, in the same rodent model does suggests that three workouts with three sets of squats (10 reps each) per week may offer the protection against corticosteroid induced muscle loss decreased skeletal muscle GLUT-4 expression and insulin resistance, leucine does not have to offer.... well, at least as long as you abstain from leucine supplementation, because the latter had the exact same detrimental effects in the 2011 study where it was administered to one of the experimental groups in conjunction with resistance training as it had in these more recent experiments in the absence of any type of workout (Nicastro. 2011). 

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