The art of resistance training is rife with “broscience,” pseudo-intellectual claims that permeate the gym despite being routinely disproven by scientific research. After years of growing up in the gym and then several years of training on an active path to make myself stronger and better, I think I’ve heard most of these adages. Now that most of the people around me know that I follow a ketogenic diet, I get some great responses.
The one that drives me craziest, however, is this:
“I mean, yeah, I think a ketogenic diet is great for a cut and everything, but you can’t train while ketogenic because you’ve got depleted glycogen.”
This is one of the most common critiques of the ketogenic diet. Depleted glycogen and no carbohydrates to replenish glycogen must mean impaired exercise right? Well, this is what your trainer or common internet article may tell you leading you to believe that for a resistance training individual, keto may not be the best option for you. Before we jump to conclusions, let’s first give a very high level overview about the physiology of ketosis as it pertains to resistance training and glycogen storage to see if this is true. We’ll begin by discussing glycogen. Glycogen is nothing more than glucose molecules bound together to form long chains. These chains are largely found in two places that we are concerned about for the topic at hand.
The liver, a vital organ, can store around 70-100g of glycogen. Since the cells of the liver contain an enzyme called glucose-6-phosphatase, they can readily release glucose into the blood stream and raise blood glucose levels. This is done in response to a signal from glucagon that the body is becoming hypoglycemic, a term meaning “low blood sugar.” The body’s transportable “glucose fuel tank” is the liver, and the tank isn’t terribly large – around 300-400 calories at most.
The muscle tissue has a glucose transporter called GLUT4 that can take circulating glucose from the blood and bring it into the cell for immediate energy use or to be stored for later use (as glycogen). The maximal capacity of the muscles to store glucose as glycogen is around 400g, although this number varies based on the amount of muscle mass of the individual. The challenge of using this glycogen to make glucose is that there’s not exactly a lot of it and secondarily it’s entirely trapped within the cell. That’s right…once the glucose is transported into the cell, muscle cells lack the ability to release that glucose back into the blood stream, meaning that tissues outside the body can’t access it. It’s a one-way ticket.
Now that we understand glycogen storage, we need to understand that the body is seldom truly depleted of glycogen. When glycogen depletion actually happens, negative things occur, such as the ever feared “bonk” that endurance athletes are familiar with.
The resistance training community has the common thought that glycogen is easy to deplete and that this can happen at accelerated rates. The ketogenic individual has diminished but not completely depleted liver glycogen. Muscle glycogen depletion, however, is a bit more interesting a topic for the conversation at hand.
After scrubbing the research, 30 minutes of exercise in a lifting/recovery ratio of 1:2 or 1:3 yielded around 20-40% glycogen depletion in the muscle tissue of the tested subject (some were not human studies). Even something as demanding as an entire professional soccer match was yielding 50-90% glycogen depletion, with the more recent and more accurate results being closer to 50%.
So, what’s the takeaway? It’s REALLY difficult to completely deplete muscle glycogen, and neither ketosis nor the exercise we think of as highly glucose-demanding is sufficient to do so unless carried out over exceedingly long periods of time at exceedingly high intensity, which may not be applicable to the majority of the population.
Now that we understand the physiologic aspects of glycogen supply and depletion, let’s talk about the issue of repletion – how do we get more when we have have burned through a large portion of our reserves? That is, after all, the real criticism of a ketogenic diet and heavy resistance training, right? You don’t have any glycogen left in the muscle and you can’t make more.
Well let’s take a look at the research. First, it may be important to address how critical muscle glycogen replenishment is. Many resistance training individuals may believe that glycogen is essential to produce positive adaptations from their training. However, one study demonstrated that neither the anabolic window nor protein synthesis was decreased due to diminished muscle glycogen (1). This could mean that if you are concerned with muscle glycogen regarding your training adaptations, you can breathe a sigh of relief. Note that this only addresses one issue. It is plausible to think that having diminished glycogen stores could affect your training intensity, which could offer an additional concern to those considering a ketogenic diet. But is it possible that ketogenic dieters can also replete glycogen?. One 1993 study tested 8 non-trained subjects and determined that even when training fasted and recovering with only water, 75% of pre-exercise glycogen had been restored in the muscle cells (2). In other words, glycogen was replenishing without carbohydrates. More research by Volek found that long-term ketogenic dieters not only have similar pre-exercise levels of glycogen but also deplete glycogen slower AND replete glycogen at a similar rate compared to long-term carbohydrate-adapted athletes (3). Even though the athletes in this study were endurance training, this still proposes that an athlete following a ketogenic diet is not only sparing muscle glycogen but also replenishing it without the use of carbohydrates. This is likely an adaptation that occurs following longer adherence to the diet and becoming fully keto-adapted.
So let’s just go ahead and kill the broscience now. Resistance training is not only possible in a ketogenic diet, but neither the anabolic response, muscle protein synthesis, nor glycogen repletion have been demonstrated as material limitations of performance in the gym. One could argue that for bleeding edge Olympic-caliber athletes, the difference in glycogen repletion matters, but for everyday exercisers like most of us, there appears to be no performance decrease in resistance training after keto -adaptation occurs. It is important to note that some of the above adaptations discussed in this article may only occur following complete adaptation to the diet, meaning training may be impaired initially, however, most individuals find that after sticking to the diet, strength and performance in the gym typically return!