Post-Workout Glycogen Repletion - The Role of Protein, Leucine, Phenylalanine and Insulin. Plus: Protein & Carbs How Much do You Actually Need After a Workout?

Pascal Behrenbruch, German decathlete and one of those athletes whose performance during a meet will certainly depend on "optimal" glycogen repletion between the different sports.
Within the past couple of weeks I have often talked (on the Science Round-Up) and written (here at the SuppVersity) about the importance of glycogen repletion to maintain optimal exercise performance and stave off the metabolic downregulation that's a characteristic of the nasty combination of overtraining and undereating. The recent post on the anti-plateau effect of sucrose should actually have made it quite clear: Even when you are "just" dieting, you should make it a priority to satisfy your body's desire to have an adequate reserve of glucose in the muscle and more importantly the liver.

But what does that mean? Do you really have to guzzle gallons of sugar water (aka weight gainers) after a workout? Certainly not.

The notion that you need to flood your skeletal muscle tissue with sugar right after the workout and that even showering before you do so would compromise your training success and put you at danger of losing muscle is simply hilarious.

That being said, the results of the latest study from the Institute of Sport at the Carnegie Faculty of the Leeds Metropolitan University in the UK is probably of greater importance to professional athletes like triathletes, decathletes, cyclists, etc. After all, they are the ones for whom immediate glycogen repletion can make the difference between victory and defeat. On the other hand, this does not mean that there wasn't something to be learned from the data Detko et al. gathered by the means of 13C magnetic resonance spectroscopy - after all, they took a different approach to the problem and did - instead of modifying the carbohydrate source - try to elucidate how the addition of protein would influence the restoration of muscle and liver glycogen in the immediate vicinity of a workout (Detko. 2013).

Is there even such a thing as an "optimal PWO glycogen replenisher"?

The quest for the optimal PWO carbohydrate source has long been a quest for the highest GI carbohydrate. Until the low carb craze hit home, the mainstay paradigm of figure, bodybuilding and performance athletes was "the higher the GI, the faster the uptake, the greater the gylcogen (re-)synthesis, the better the results". From a scientific perspective, it has has yet long been refuted that the GI and thus the insulin response a given carbohydrate would elicit was the only determinant of its practical value as a muscle (let alone liver) glycogen replenisher.

Did you know that there is a catalytic dose of ~40g of fructose per day (=6 normal size bananas) that will improve your glucose metabolism? (learn more)
One of my favorite and in fact comparably recent studies that demonstrates the fallacy of using the glycemic index as a gauge for post-workout glycogen replenishment is the 2008 study by Wallis et al. In a well-controlled experiment, the researchers were able to show that a post-workout drink that contained 2:1 glucose to fructose ratio was on par with pure glucose in its ability to replenish the depleted muscle and liver glycogen, when it was consumed right after a standardized glycogen depleting exercise bout (Wallis. 2008). Obviously, this result stands in stark conflict with the "glycemic index (GI) hypothesis". After all, the falsely dreaded fructose, the demon of Dr. Lustig's worst nightmares, has a GI of <20 and thus the lowest glycemic index of all natural sugars.

If the "GI hypothesis" was accurate, fructose should therefore be by far the worst choice for an athlete who wants to replete his / her glycogen stores as fast as possible. That this is not the case, goes to show you that things are - once again - much more complex, than the widely accepted, but overtly simplistic "rules of thumb" would suggest.

Why is the glycemic index a bad avisor, when it comes to PWO glycogen replenishment?

Before we head on to the new data the Detko study has to offer, let's briefly take a look at why the glycemic index does not qualify as a compass to guide us on our quest for the perfect post-workout carbohdydrate source. Don't worry, I am trying to cut myself short, just listing the four most important caveats:
  • Table 1: It's rarely talked about, but especially endurance athletes will also benefit from increased intramuscular lipid stores. Therefore the overview of the intramuscular glycogen and lipid storage rates from a 2003 paper by Jacques Décombaz could come especially handy to the marathoners among the SuppVersity readers (Décombaz. 2003)
    Non-insulin-dependent glucose uptake: In the first 30-60min after a workout, for example the GI, i.e. the ability of a given carbohydrate source to trigger an insulin release is negligible, simply because the non-insulin dependent uptake of glucose into the muscle is already maxed out.
  • Organ specificity: Contrary to the skeletal muscle tissue, the liver has a is downright dotty about fructose; and the more fructose it takes up, processes it and turns it into glycogen (see pathway, here), the more glucose will remain for your muscles to feast on.
  • Ceiling effects: The amount of glycogen your muscles can synthesize is limited to approximately 9–10mmol/kg wet weight (WW). This rate can be sustained by the intake of 1.2g of carbohydrates per kg of body weight - more cannot end up in your muscle, regardless what kind of useless nutrient partitioner the company rep in disguise on your favorite bulletin board may have persuaded you to buy.
  • Figure 1: Muscle glycogen content 2h into the recovery period (left) and rise and fall of glucose concentrations after the ingestion of a low and high molecular weight starch immediately after a standardized glycogen depleting exercise bout (Gunnar. 2012)
    Molecular weight and absorption dynamics: While it is obvious that the latter should have a major effect they should (a) interact with the glycemic index (faster appearance in the blood = greater insulin response in healthy individuals) and (b) warrant the use of carbohydrate blends (after all, you don't want to run out, after the intitial spike, right). From my use of the conditional in the previous paragraph you may however already have realized that this assumption is not unambiguously supported by the currently available literature which does support the faster transit times, but not necessarily the purported downstream effects on the repletion of the glycogen stores in exercised muscles.
    In his 2012 thesis, Frances Gunnar from the University of Nottingham, for example, demonstrated that the much praised high molecular weight starch Vitargo(TM) did not yield produce greater increases in post-workout glycogen resynthesis than a low molecular weight counterpart (Gunnar. 2012). On the other hand, we have seminal papers such as the Y2k paper by Piehl et al. that are usually cited in this context (Piehl. 2000) and in which solutions with high molecular carbohydrate sources yielded greater rates of skeletal muscle re-synthesis.
I guess these were more than enough, "on the other hands" as Carl Lenore likes to call these lengthy departures of mine on the weekly SuppVersity Science Round-Up on the Super Human Radio Network from time to time. So let's now finally get to the study at hand.

Protein and galactose? What's that got to do with PWO glycogen repletion?

As I already hinted at in the introduction, the experiment Detko et al. conducted was not designed to compare carbohydrate solution A with carbohydrate solution B. The idea was rather to elucidate whether and by which mechanisms the addition of protein to the a standardized post-workout carbohydrate solution could accelerate the PWO glycogen repletion even further. Accordingly the test solutions the scientists prepared from commercially available raw materials contained either
  • maltodextrin + galactose - 0.9 g/kg body mass (BM) maltodextrin + 0.3g/kg BM galactose, or
  • maltodextrin + glactose + protein + leicine + phenylalanine - 0.5g/kg maltodectrine, 0.3g/kg galactose, 0.2g/kg whey and 0.1g/kg of each leucine and phenylalanine
As subjects, the scientists selected a total of seven recreationally, yet highly trained male cyclists who had been training for least 10h per week over the least 5 years (mean age: 33y, body weight: 79kg, VO2Max: 58 ml/kg per min).
It would have been more promising to use isoleucine instead of leucine and phenylalanine as "additives" to boost glucose uptake (click here to learn why)
Why would the scientists use galactose, leucine and phenylalanine? According to previous research the combination of maltodextrin + galactose has a slight, but significant advantage over the glucose + fructose combination mentioned earlier in this article. Practically it's unlikely that it will make a significant difference, anyways. After all, the important thing here is that fructose and galactose are preferred glycogen sources of the liver, which is thus not going to "steal" the glucose from the maltodextrin which is supposed to end up in the glycogen stores of the musculature - not the live (Decombaz. 2011).

The addition of leucine and phenylalanine, on the other hand, was supposed to increase the insulin response and thus help to shuttle the glucose into the cells. Needless to say that this is not necessarily a good idea and actually based on the same fallacious notion that insulin would be the main determinant of the rate of glucose replenishment after a workout, right?
In order to prevent differences in the baseline diet to interfere with the study outcome, the participants were not only asked to reproduce their nutrient intake in the days prior to the two testing sessions, they were also provided with standardized meals. which containing 150 g CHO, 67 g PRO and 22 g fat  and had to be consumed on the evening before the tests which consisted of
  • 45min of steady state cycling at 70% VO2max,
  • 6x1min sprints at 120% of the VO2max (2min recovery at 50% VO2max) and 
  • 45min of steady state cycling at 70% VO2max
The steady 2nd state part of the intervention was meant to "further promote [the] depletion of glycogen in type I fibres" and to elicit a "reduction of plasma lactate concentrations at the end of the glycogen-depleting exercise".

"Ok, I got it, what about the supps and the results?"

During the trial the subjects were free to consume as much water as they wanted. Blood samples were drawn at the start, 45min after the intervention and every 30min during the 4h recovery period. The crucial part of the study, the supplementation, took place immediately after the first vastus lateralis scan. The drinks were ingested in a single 400ml bolus and 6 smaller 150ml portions every 30 min (see figure 2, left - small bottles).
Figure 2: Outline of the experimental design (left) and glycogen repletion rates - calculated based on averages for all subjects over the full course of the 4h post-workout window (Detko. 2013)
As you can see in figure 2, the averaged glucose repletion rates were virtually identical with a non-significant, but visible advantage for the muscular glycogen with higher carbohydrate and no protein intake. The result clearly refutes the researchers initial hypothesis that
"[...] the post-exercise ingestion of MD and GAL with PRO and AA would enhance liver and muscle glycogen repletion compared with an isoenergetic MD–GAL formulation." (Detko. 2013)
What's particularly intriguing about this result is that it manifested despite the fact that the large spike in insulin, the researchers had expected in response to the addition of whey and the pro-insulinogenic amino acids leucine and phenylalanine to the mix (see figure 3).
Figure 3: Blood glucose and insulin levels in the post-workout period (my markups in Detko. 2013)
In conjunction with the data about the glucose concentration, which did not crash in response to the insulin spike (this should happen if the equation "more insulin = more glucose uptake = faster glycogen replenishment held) this just confirms that the effects of the carbohydrate, protein and amino acid induced insulin spikes have little to no effect on the rate post-workout glycogen re-synthesis. While previous research suggests that a threshold limit must be maintained to keep the influx of glucose constant after the initial ~30min, this threshold is so low that any special "tactics" to increase the insulinogenic effect of post workout-nutrition appears to be a waste of time.

Bottom line: If we follow the Taubsian mantra that insulin is the root cause of all disease, the necessary conclusion we'd have to take away from the results of this study is that you better avoid having protein in your post-workout nutrition and rather resort to carbohydrates alone... just kiddin' ;-) We obviously all know about the benefits the ingestion of a fast digesting protein in the vicinity of workout has on protein synthesis. Simply skipping on the protein fraction of your post-workout shake is therefore not really an option. After all, the transient increase in insulin, as useless as it may be, is probably not going to kill you.

That being said, this is study #2 within no more than a week that questions the usefulness of adding leucine as a free-form amino acid to your supplement stash (compare "Leucine Supplementation Exemplifies Potential Downsides of Non-Specific Insulin Sensitizers"). With ~30g of whey you should have enough readily available amino acids (including leucine!) to kickstart protein synthesis, anywa - plus: contrary to the average study participant in this and similar experiments, you are not going to fast for the next 4h, so that the protein from your next full meal is going to help you keep the plasma amino acid levels steady (Tip: If you cannot have a full meal, afterwards add 20g of casein to the shake).

What happens if you eat 194 bananas in 3 weeks? You will get fit and sick, right? No, false. What actually happens is a reduction in body fat (read more)
With your protein needs taken care of, the only other thing you'll need are some carbohydrates to satisfy your bodies desire to refill its glyocogen stores. Preferably, those carbs come at a ratio of 2g of muscle substrate (=glucose or precursors) to 1g of liver substrate (=fructose or galactose). A banana, a food I have previously recommended as a post workout carbohydrate source, would provide you with 5g of free glucose and 5g of free fructose (per 100g). It does however also contain 5g of starch, 2g of sucrose and 2.5g of fiber, so that you would end up with a 2:1 ratio of glucose (+starch) to fructose and thus "right in the zone" (if you really need to replete your glycogen levels as fast as possible, you will have to resort to non-whole food sources, though).

With 32g of carbs a single large banana (~140g) would get you up to a 1:1 ratio of protein and carbs and thus to the lower end of what I would consider a rational post-workout nutrient mix. If you (a) don't follow that up with a real meal, when you are back from the gym, it is probably smart to double the amount of minimal carbs. While this would be the bare minimum, your diet (low or high carb), the respective carbohydrate allowance (limited to X g of carbs per day), your current goals (cutting or bulking, perfromance of body composition changes) and obviously your individual "carb tolerance" (rule of thumb: the leaner the better) dictate how much you can our rather should add to that to see optimal results. And as the results of the study actually underline, only very few of the SuppVersity readers will have to go past the 1g/kg body weight margin, as long as this is not their only carbohydrate containing meal of the day.

  • Décombaz J. Nutrition and recovery of muscle energy stores after exercise. Schweizerische Zeitschrift für Sportmedizin und Sporttraumatologie. 2003; 51 (1): 31–38.
  • Décombaz J, Jentjens R, Ith M, Scheurer E, Buehler T, Jeukendrup A, Boesch C. Fructose and galactose enhance postexercise human liver glycogen synthesis. Med Sci Sports Exerc. 2011 Oct;43(10):1964-71.
  • Detko E, O'Hara JP, Thelwall PE, Smith FE, Jakovljevic DG, King RF, Trenell MI. Liver and muscle glycogen repletion using 13C magnetic resonance spectroscopy following ingestion of maltodextrin, galactose, protein and amino acids. Br J Nutr. 2013 Feb 6:1-8.
  • Gunnar, F. The effects of a high molecular weight glucose polymer on muscle metabolism and exercise performance in humans. Thesis submitted to the University of Nottingham. July 2012. 
  • Piehl Aulin K, Söderlund K, Hultman E. Muscle glycogen resynthesis rate in humans after supplementation of drinks containing carbohydrates with low and high molecular masses. Eur J Appl Physiol. 2000 Mar;81(4):346-51.
  • Wallis GA, Hulston CJ, Mann CH, Roper HP, Tipton KD, Jeukendrup AE. Postexercise muscle glycogen synthesis with combined glucose and fructose ingestion. Med Sci Sports Exerc. 2008 Oct;40(10):1789-94.
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