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Carbohydrate Periodization – The Strategic Manipulation of Dietary Carbs to Enhance Endurance Performance

Confuse the muscles! Shock the system! Trick your body!

 Cyclic Ketogenic Diet

Saying any of the three phrases above are different ways that people fully admit to knowing nothing whatsoever about how our bodies adapt to training. Sure, they’re (almost) catchy phrases, but they are completely ridiculous. Muscles don’t get confused or tricked because they don’t think; they have no thought processes. They do have mild electrical currents, but to suddenly overwhelm the body’s capacity for exercise is a recipe for disaster – that is why we TRAIN for athletics in the first place! Otherwise, we could just sign up for a marathon, shock the system, and then casually return to the couch while we wait for chiseled bodies to take form.

Unfortunately, that’s not quite how it works. Those silly phrases are just used as substitutes for a more complex and scientifically-appropriate word – periodization.

Periodization is systematic and planned variation in a program, typically a training program. While we sure do love talking about periodized training, we can’t help but shed some light on periodization of the diet. Often, the two go hand-in-hand, as an athlete should be dieting to meet their athletic demands and to realize their physical goals, whether they are for endurance performance, strength, or physique. In a simple example, you go from training 4 days per week on an average 2,300 Calories per day to training 6 days per week, so you increase Calories to 2,500 per day to help meet the demands of training. This makes perfect sense, and it is an appropriate adjustment. However, there is more we can do to get faster and improve our performance.

Diet Archetypes

Targetted Ketogenic Diet

But first, we need a little background on a few of the different major dietary paradigms. These dieting archetypes can be grossly categorized as high carb, low carb, and no carb (by no carb, I mean the individual is striving towards no carb, but likely eating very few carbs). Protein usually stays somewhat constant, and fat varies indirectly with carbohydrates. Said differently, if carbs go up, fat goes down, and vice versa.

And if you’re wondering about the phrasing here, it is deliberate. It was a conscious choice to say, “diet archetype,” because that is what diets are nowadays – an attempt to fit into an ideal pattern or mold so much so that people unnecessarily stress over hitting their numbers. Part of the point of this article is to describe how one dieting archetype is not always superior to another, and the truly perfect example of a diet is one that changes and adapts.

High Carb Diets

High carb diets are the standard diets prescribed to Americans and athletes. Because our mission is to improve athletes’ physical capacity, we’re going to focus on the dietary needs associated with sport. In this sense, high carb diets are probably something you have heard of before, which 50-70% of total Calories come from carbohydrates (carbs contain 4 Cals per gram). High carb diets are also low in fat (20-30% Cals) and moderate in protein (15-20% Cals). High carb diets are popular among athletes, nutritionists, and scientists because carbohydrates are the primary fuel source during exercise*. Emphasis on the asterisk.

Low Carb Diets

One important distinction that needs to be made immediately when discussing this topic is low-carb is NOT the same as ketogenic. The two share similar aspects, but they are two distinct types of diets. Low-carb diets contain 20-40% of Calories as carbohydrate, ~20-30% as protein, and 20-40% as fat. Paleo diets and Mediterranean diets often fall into the low-carb category. Low carb archetypes generally understand the health benefits of monounsaturated fats like walnuts or olive oil, while maintaining admonishments of reduced saturated fat intake. The healthful aspects of protein are well understood as well as the benefits of fish and omega-3 fats that accompany the lean protein in fish. The common theme here is health, and most athletes assuming a low carb diet does so for health reasons, including a mild fat-adaptation.

“No” Carb Diets

What we’re calling no carb diets in this article do include ketogenic diets. For our purposes, “no” carb diets are ones with a primary goal of reducing carbohydrate intake to a nearly complete or fully complete (such as with the carnivore diet) degree. These diets include 0-10% of Calories as carbs, 20-40% as protein, and 50-75% as fat. Due to the severe restriction of carbohydrates, these diets are almost always ketogenic diets, as they result in the generation of ketones from fat. Athletes’ purposes for taking on a no carb diet are typically for fat loss, cognitive clarity, and a metabolic shift onto fat, presumably as body fat to increase the size of the fuel tank for endurance training and the facilitate reduction of body fat stores.

P.S. I am aware that 11-19% and 41-49% carbs are not defined. This is a gray area inside of another grayer area that isn’t important enough to comment on for the purposes of this article.

The Asterisk. Explained.

Best carbohydrates for athletes

Do you remember the *? Of course you do, it was only 2 paragraphs ago, and if you were not existentially offended by the opening rant about muscle confusion, you’re intelligent enough to remember what happened 5 minutes ago. Carbohydrates are the primary fuel source during exercise*. This is not necessarily untrue, but we can only see as well as the looking glass allows us. What I mean is, carbohydrates are perceived to be the body’s preferred fuel source because that is what is made available. When we study the “preferred fuel source” we are studying it in humans that are consuming a high carb diet.

Fortunately, we’ve made this realization and swapped out the looking glass for a fresh lens. When looking for the preferred fuel source in athletes consuming a no carb diet, instead of a high carb diet, fat would clearly be the preferred source under most scenarios. Do you remember the “fat-burning zone?” The fat-burning zone is an exercise intensity which “maximally burns fat.” Well, that zone is way bigger when the athlete is already fat-adapted. The fact of the matter is, carbohydrate is only the preferred fuel source during high-intensity exercise!

High-intensity exercise is known by athletes as the lactic acid type of training and all those good burns. Lactic acid is just buildup of glucose metabolic end products that cannot be completely metabolized because we’re burning through the glucose too fast for our cells to handle. There’s nothing inherently wrong with this, but fat-adaptation can make it so that we only start accumulating lactic acid at an even higher exercise intensity because at moderately high intensities, the fat-adapted athlete is still primarily using fat as fuel.

All of this is to say that we have metabolic flexibility; we can shift back and forth between fats and carbs as a primary fuel source depending on our metabolic conditioning and our exercise intensity. However, carbohydrates are the only fuel source used at the greatest of exercise intensities, which would be “all out” exercise of about 30 seconds to 2 minutes. After about 2 minutes, we can no longer maintain this type of metabolism and drift back towards our “normal” metabolisms.

A Little Something for Everyone

When is the best time to eat carbs

So which is the best diet? The answer is all of them. More specifically, it depends on your goals, and you will consume one type of diet at different times to reach different goals. In fact, you might consume different diets to meet the same goal. A great friend and mentor of mine likes to say, “The best type of diet is the one you are not on!” How does that work?

What my mentor is suggesting is that once you’ve adapted to a certain way of eating, your changes are complete. Now, that’s not to say that you cannot continue making adaptations, but the adaptations you are going to make won’t be because you are still adapting to a diet (Confuse the gut! Shock the stomach!). This leads us to dietary periodization.

We have to assume you are already varying your training. These don’t need to be dramatic changes, but you should be modifying your volume, intensity, frequency, or some other variables on a somewhat consistent basis (e.g., daily or weekly). The most common variations are volume and intensity. Do you run for one hour or two? At fast pace or moderate pace? Hill sprints or flat ground? All of these different types of modification are included in periodized training. Accordingly, you can change up your dietary patterns to meet the needs of training and/or to force the body to adapt to training under certain conditions. It’s the second part of that last sentence that is the fun part.

When and Why to Change your Diet

Diet for fat loss

Here are a few of the “rules” you may have been waiting for:

  1. Consume carbs when you need to perform. Before and/or during the exercise bout. This may be for a race, other competitive event, or high-intensity training lasting a total of 30 minutes or more. For competitive events, don’t hold back. It’s better to be safe than sorry. Of course, eating too much might make you sick. Don’t do that! Just don’t be scared to get enough.

  2. You do not need carbs for low intensity exercise (up to top end of the traditional “fat burning” zone, ~60% VO2Max). You do not need carbs for moderate intensity exercise lasting up to 60 minutes.

  3. Within an entire training year (a macrocycle, if you will), go “no carb” for at least 4 weeks, probably during the off season. Preferably, during the 4-8 weeks prior to beginning a competitive or pre-competitive phase of training, so your metabolic adaptations persist through the competitive phase.

  4. As an alternative or adjunct to rule 3, if you have the flexibility in your competitive schedule for within-day undulations in carbohydrate intake, follow rules 1 and 2 throughout the competitive season with rule #2 meaning if you don’t need them, don’t use them.

Here’s some “why.” The best stimulus for becoming a better athlete is to train. The diet supports the training, and it is the second best stimulus for becoming a better athlete. Diet periodization capitalizes on the metabolic changes that occur in response to diet. Trying to train at high intensities without carbs in the body or made available to the body will ultimately result in NOT training at a high intensity. It will be physiologically impossible to maintain an “all out” effort without carbohydrate nutrition. We say “maintain” here because no matter what type of diet you follow, you will have some muscle glycogen.

At some point however, the ability to use the glycogen effectively begins to dwindle as fat utilization increases with strict no carb scenarios. By providing carbs to exercise at high intensities then immediately using them during exercise, we maintain the ability to use the carbs while also supporting the training. Afterwards, the body can shift back into a more fat-based metabolism during rest or during low to moderate intensity activity.

Practical Examples

Carbohydrates for runners

By training at moderate intensity with low carbohydrate availability, we also train the body to make best use of fat as fuel. This can actually occur within any dietary archetype, and it has been demonstrated by scientific inquiry. Supplying adequate carbohydrates prior to high-intensity, but NOT prior to moderate-intensity, exercise improved 10km running time and decreased body fat in trained triathletes, while all athletes consumed a total of 5.5 grams of carbs per kilogram of body weight every day. This was accomplished by eating carbs in the morning before a HIIT session, then not eating carbs again until after a moderate-intensity training session the following day. Twice per week, the athletes trained twice per day: moderate-intensity in the morning, ate carbs, performed HIIT, ate no carbs, slept, and then woke up for another moderate-intensity training session. This carbohydrate consumption pattern was superior to consuming carbohydrates in an equal distribution throughout the day.

Similar adaptations may be made from different, but functionally similar approaches. Consider an opposing scenario to the one just described, which athletes consumed 5.5 g carbs/kg body weight.

Ketogenic triathletes consuming a normal diet of no carbs except for those in vegetables, nuts, and dairy can use a similar approach and NOT interrupt their overall metabolic state. A ketogenic athlete may take on the same training as was just described. However, instead of consuming the same total amount of carbs, they may just consume the carbs that will be utilized during high-intensity exercise that will preferentially burn carbs. Let’s say that they know the HIIT session will take about 200 Calories, they can go ahead and “load” 50 grams of carbs briefly before training. The ketogenic athlete will be back in ketosis the next time they eat fat or after a few hours of fasting, definitely by time the moderate intensity training session comes around, during which they will still use fat at a maximal rate.

In a Nutshell

carb backloading

Athletes need gratuitous amounts of energy. The energy can come in the form of fat or carbohydrate, with one exception previously described. Therefore, it behooves the athlete to be able to have a “dual fueling” system. One that responds well to both carbs and fat. However, under typical high carb scenarios, athletes become carbohydrate dependent, and their ability to use fat is inhibited. Conversely, a strict ketogenic diet can curb the ability to oxidize carbs (although the science is currently not thoroughly vetted). What is the athlete to do?! Utilize both diet archetypes at the appropriate times and for the appropriate reasons to acquire the best of both worlds!

References

Marquet, L. A., Brisswalter, J., Louis, J., Tiollier, E., Burke, L., Hawley, J., & Hausswirth, C. (2016). Enhanced Endurance Performance by Periodization of CHO Intake:" sleep low" strategy. Medicine and science in sports and exercise48(4), 663-672.

Volek, J. S., Freidenreich, D. J., Saenz, C., Kunces, L. J., Creighton, B. C., Bartley, J. M., ... & Lee, E. C. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism-Clinical and Experimental65(3), 100-110.

Stellingwerff, T., Spriet, L. L., Watt, M. J., Kimber, N. E., Hargreaves, M., Hawley, J. A., & Burke, L. M. (2006). Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. American Journal of Physiology-Endocrinology and Metabolism290(2), E380-E388.



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