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| Post-Workout High Isoleucine AA+CHO Decreases Glucose Spikes, But Impairs Musclular Glyocogen Resynthesis - Reason Enough to Skip Amino Acids? |
In their latest study Wang and colleagues from the University of Texas at Austin and the Shanghai Research Institute of Sports Science did just that: They studied the effects isoleucine and four additional amino acids, on blood glucose homeostasis and glycogen synthesis after strenuous exercise.
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| Table 1: Subjects’ characteristics (Wang. 2015). |
The actual tests consisted of cycling on an ergometer to deplete muscle glycogen. Blood sampling and a muscle biopsy were performed immediately on cessation of exercise. After the muscle biopsy, subjects were given the first of two supplement doses. More specifically they received either..."Two to three days after the VO2max test, the subjects reported to the laboratory to perform a practice ride to familiarize them with the laboratory environment and the experimental protocol. The practice ride was also used to adjust and verify appropriate workloads for the experimental trials. The practice rides simulated the protocol ride but without blood samples or muscle biopsies being taken. The ride consisted of cycling at 70 % VO2max for 2 h, which was followed by five 1-min sprints at 85 % VO2max. The sprints were separated by 1 min cycling at 45 % VO2max. During the first 15 min of each hour, oxygen uptake was measured for 5 min to verify workload.
Figure 1: Basically the AA supplement contained almost exclusively isoleucine. It was administered in the dosage shown above and at twice that amount in the LAA and HAA trials (Wang. 2015)
Water (250 mL) was provided every 20 min of exercise. Heart rate (HR) was monitored and ratings of perceived exertion (RPE) on a Borg-scale (ranging from 6 to 20) were collected every 30 min of exercise. The practice ride and each of the following three experimental trials were separated by a minimum of 7 days and maximum of 12 days" (Wang. 2015).
- 1.2 g carbohydrate/kg body weight (CHO), 1.2 g carbohydrate/kg body weight plus 6.5 g AA (CHO/LAA) or
- the same carbohydrate supplement plus 6.5g (CHO/LAA) or 13 g AA (CHO/HAA)
Why would you even believe that there may be benefits from AA supplementation?
As Wang et al. point out, "this amino acid mixture was selected as it was previously reported to be more effective in lowering the blood glucose response to a glucose challenge than isoleucine alone" (Wang. 2015) by Bernard et al. (2011).
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Figure 2: Blood glucose AUC during the oral glucose tolerance test (OGTT). Sprague-Dawley rats were gavaged with either glucose (CHO), glucose plus a 5-amino acid mixture (CHO-AA-1), glucose plus a 5-amino acid mixture with increased leucine concentration (CHO-AA-2), or placebo (PLA). Blood was taken from the tail immediately before the gavage and 15, 30, 60, and 120 min afterward (Bernard. 2011). |
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| Figure 3: Blood glucose postexercise and during the 4-h recovery. Treatments were with CHO (circle), CHO/LAA (triangle), and CHO/HAA (filled circle) supplements provided immediately after and 2 h after exercise. Values are mean ± SE. CHO/HAA vs. CHO (*p < 0.05). CHO/LAA vs. CHO (# p < 0.05) - left; Blood glucose area under the curve (AUC) during the 4-h recovery. Treatments were CHO, CHO/LAA, and CHO/HAA supplements provided immediately after and 2 h after exercise. AUC was calculated with baseline (pre). Values are mean ± SE. CHO/HAA vs. CHO (*p < 0.05). CHO/LAA vs. CHO (# p < 0.05) - right (Wang. 2015). |
Glucose modulation without glycogen optimization?! How does that work? Well, obviously glucose can also be oxidized or used to replete ATP in the muscle. It is at least no real news that isoleucine will decrease glucose levels in the blood and increase glucose uptake in the muscle without, however, producing increased glycogen levels. For example, Doi et al. (2005) reported that an oral administration of 1.35 g/kg isoleucine in food-deprived rats significantly decreased the plasma glucose concentration and increased glucose uptake in the muscle of rats without an increase in muscle glycogen storage.
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| Figure 4: Total muscle glycogen storage in the vastus lateralis during the 4-h recovery from intense cycling. Treatments were CHO, CHO/LAA, and CHO/HAA supplements provided immediately after and 2 h after exercise. Values are mean ± SE. CHO/HAA vs. CHO (*p < 0.05 | Wang. 2015) |
As the data in Figure 4 shows, the exact opposite was the case. After 4h of recovery the muscle glycogen levels were not higher, but lower in the amino acid supplemented trials.
For diabetics this wouldn't be a problem. For athletes it's yet clearly a disadvantage that the 4-g recovery glycogen levels were lower and significantly lower in the low and high dose amino acid supplement trials.
Eventually this result is surprising because specifically in the high amino acid group (a) the insulin levels, (b) the AS160, a protein that controls insulin mediated glucose uptake, (c) the mTOR & p-AKT levels, (d) the "exercise hormon" levels of serum irisin and (e) the levels of glycogen synthase which stores carbs in forms of glycogen in the high dose AA trials were significantly elevated.
Bottom line: While the study at hand did confirm that isoleucine (in conjunctio with other, but probably irrelevant amino acids) will improve the glucose response to high GI carbohydrates, it did not confirm the assumption that this makes isoleucine the ideal intra- and/or post-workout amino acid to optimize glycogen synthesis and thus post-workout recovery. For diabetics the increase in insulin and the corresponding decrease in glucose response still is a major plus. This assumes that the insulin increase occurs in the obese (in previous studies by Wang et al. (2012) an increased insulin release to a high isoleucine AA mixture was not observed) and / or that there is an independent effect of the amino acid mixture on glucose uptake in the muscle or the periphery.
For athletes, however, it appears to be detrimental as it reduces the rate of muscle glycogen synthesis after workouts and puts a questionmark behind the "repartitioning effects" of amino acids - if there is a repartitioning effect involved, here, it would be away from the glyocogen stores of your muscle. An effect that may be related to the increase in mTOR which triggers protein synthesis via p70S6k which inactivates the glycogen synthase kinase-3 (Armstrong. 2001). This would indicate that you cannot have both maximal protein & glycogen synthesis and thus relativize the obvious conclusion that isoleucine supplements are not suitable for athletes. What it won't do, though, is to provide the missing evidence that amino acid supplements have an advantage over whey, which has been shown to increase glycogen synthesis and storage (Morifuji. 2005, 2010; Zawadzki. 1992; Ivy. 2002, 2008) - why would you use AAs, then? | Comment on Facebook!
References: |
| In contrast to the high isoleucine amino acid supplement that was used in the study at hand, plain whey protein does increase glycogen storage after workouts - significantly, as the data Ivy et al. generated in a 2004 randomized controlled human study involving well-conditioned subjects observed (Ivy. 2004). |
- Armstrong, Jane L., et al. "Regulation of glycogen synthesis by amino acids in cultured human muscle cells." Journal of biological Chemistry 276.2 (2001): 952-956.
- Bernard, Jeffrey R., et al. "An amino acid mixture improves glucose tolerance and insulin signaling in Sprague-Dawley rats." American Journal of Physiology-Endocrinology and Metabolism 300.4 (2011): E752-E760.
- Doi, Masako, et al. "Isoleucine, a potent plasma glucose-lowering amino acid, stimulates glucose uptake in C2C12 myotubes." Biochemical and biophysical research communications 312.4 (2003): 1111-1117.
- Ivy, John L., et al. "Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement." Journal of Applied Physiology 93.4 (2002): 1337-1344.
- Ivy, J. L., et al. "Post exercise carbohydrate–protein supplementation: phosphorylation of muscle proteins involved in glycogen synthesis and protein translation." Amino acids 35.1 (2008): 89-97.
- Morifuji, Masashi, et al. "Dietary whey protein increases liver and skeletal muscle glycogen levels in exercise-trained rats." British journal of nutrition 93.04 (2005): 439-445.
- Morifuji, Masashi, et al. "Post-exercise carbohydrate plus whey protein hydrolysates supplementation increases skeletal muscle glycogen level in rats." Amino acids 38.4 (2010): 1109-1115.
- Wang, Bei, et al. "Amino acid mixture acutely improves the glucose tolerance of healthy overweight adults." Nutrition Research 32.1 (2012): 30-38.
- Zawadzki, K. M., B. B. Yaspelkis, and J. L. Ivy. "Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise." J Appl Physiol 72.5 (1992): 1854-9.