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Nutrition for Metabolic Adaptation and Performance

By Gaelle Abecassis | Dec 4, 2022

Carb Periodization Explained

As we discussed in our previous blog, carbohydrates are the most recommended energy source for endurance athletes looking to achieve optimal performance during competitions and intense training. In recent years, however, we’ve seen more athletes turning to low-carb diets to increase their fat-burning capacity at moderate intensity and reduce the need for carbohydrates during long training and races. Others use this dietary approach to improve their body composition. Still others follow the low-carb method to avoid a high-carb diet that can result in metabolic imbalances and lead to chronic inflammation, high blood sugar, or insulin resistance. However, many of these low-carb diets are also high in fat. This poses a problem because a high-fat approach also has its drawbacks, the most obvious being compromised training quality, reduced performance at higher intensities, and diminished ability for muscle cells to oxidize glycogen efficiently.¹

Periodized nutrition offers an excellent alternative to the extremes of low-carb or high-fat diets. This base phase of this approach, which is now encouraged by the sport nutrition guidelines, limits your carbs during your off-season — when your training intensity is low and can be fueled by fat — but increases your carb intake as you move into your build and peak phases, where your training requires higher intensity and longer duration. You can go one step further and adjust your carb intake for each session depending on your training goal. This practice, known as carb periodization, can produce favorable metabolic adaptations that increase fat oxidation at higher intensities, enhance exercise performance, and improve metabolic flexibility.

By following this periodization, you will adjust your carb intake to your training requirements and experience the benefits of optimal performance, improved training quality, and positive metabolic adaptations.²

With those enhancements in mind, let’s explore carb periodization with a focus on low-carb training, the mechanisms and metabolic adaptations in play, the potential benefits you can get from this practice, and how to incorporate it into your training and nutrition routine.

What Is Carb Periodization?

Carbohydrate periodization is the manipulation of carbohydrate availability on a day-to-day or meal-by-meal basis according to the intensity, duration, and goals you have planned for an upcoming workout. Adjusting your carb intake can enhance the desired outcome for that session.

•If you want to perform optimally, train at high intensities or for long durations, ensure high-quality outputs, reduce symptoms of fatigue and overreaching, and maximize your recovery, you should train with full glycogen stores. To accomplish this, your pre-training carb intake should be high, and you may need to supplement with additional carbs during exercise. (The standard recommendation is 30-60 g of carbohydrates per hour). You should also consume carbs post-exercise to allow glycogen restoration and proper recovery.

•If you want to train your gut, you can increase your daily carbohydrate intake or boost your mid-exercise carb consumption to improve your gut absorptive capacity and reduce GI discomfort.

•If you want to train your race nutrition, you should implement all aspects of your race nutrition strategy (food, gels, drinks, supplements, timing, etc.) in your training session.

•If you want to enhance the metabolic adaptations of your skeletal muscle that will develop your fat metabolism, improve your metabolic flexibility, and possibly enhance your time to exhaustion during exercise and your performance, you should periodically train with low-carb availability. ^1,2,3

The chart below indicates the metabolic adaptations you can expect from a workout depending on your exercise duration, exercise intensity, starting muscle glycogen, and pre-exercise nutrition.

Figure 2 - Metabolic Adaptation

Because training low has potential advantages for your performance and health, let’s explore this approach, how to include it in your training and how it can benefit you.

Low-Carb Training

Mechanisms in Play at a Cellular Level

Low-carb training appears to enhance some molecular signaling pathways in the muscle cells, specifically those associated with adaptations that can benefit endurance sports. Exercising with low glycogen availability can activate key cell-signaling proteins (e.g., AMPK, p38, PPAR, PGC-1α) that upregulate the expression of genes involved in mitochondrial biogenesis, lipid oxidation, and angiogenesis.

•Increased mitochondrial biogenesis means more mitochondria in the muscle cells, thus greater capacity to produce cellular energy and potentially increase endurance capacity and performance.

•Increased lipid oxidation enables more fatty acids to be used for energy production at higher intensities, sparing glycogen in the process.

•Angiogenesis supplies the muscle with a greater blood supply, which improves the delivery of nutrients and oxygen to the working muscles.^1,4

How To Implement Low-Carb Training

There are several ways to train with low-carb availability.

•Train fasted. After an overnight fast, train before breakfast. With this method, while muscle glycogen levels may be normal or even high, liver glycogen levels will be low. This permits increased free fatty acid availability and activation of the AMPK signaling, enabling lipid oxidation and other positive metabolic adaptations. However, such adaptations are likely due to carb restriction only, as opposed to complete fasting, so you may consume some protein (e.g., 20g of whey protein) before or during the session. This approach will allow the same adaptations while improving net muscle protein balance.^1,2,3

•Train twice a day. Do your first workout of the day after consuming some carbs, and then don’t eat any carbs before your second workout. Your first session will lower your muscle glycogen so that you perform your second training in a low-glycogen state. This method has been shown to increase oxidative enzyme activity and fat utilization and improve exercise capacity and performance.^1,2,3

•Sleep low. Train in the evening, restrict carbs overnight and do a fasted session in the morning. The effect is similar to training twice a day, except that the duration with low muscle and liver glycogen is extended for several hours while you sleep. Studies using this method have demonstrated beneficial effects on cell signaling and performance.^1,2,3,5

•Recover low: Don’t consume carbs for 2-4 hours post-exercise, not even with your usual recovery meal. By restricting carbs post-exercise, you keep muscle and liver glycogen low, extend the availability of circulating free fatty acids for fuel, sustain the upregulation of cell signaling pathways, and boost the adaptive response to the session. Some studies have also reported an improved metabolic adaptation to exercise using this method.³

Performance Benefits

Low-carb training can improve endurance capacity and performance due to enhanced mitochondria biogenesis and increased blood supply to working muscles.^1,4 However, while some studies saw performance improvements in sub-elite athletes with a Sleep Low approach,⁵ a recent meta-analysis concluded that evidence of performance enhancement associated with carb periodization in well-trained endurance athletes is limited. As such, low-carb training is not necessarily associated with enhanced endurance.⁶ That said, while not all studies have shown a long-term performance benefit, none have shown a drop in performance.

A clear benefit of low-carb training, though, is improved fat oxidation. This occurs because you are conditioning your body to use its stored fat as fuel instead of recently consumed carbohydrates.^1,4 This may benefit your body composition and increase the intensity at which you can exercise while predominantly using fat as fuel, sparing glycogen stores, which allows you to last longer without carb intake during long training sessions and races. This benefit may be advantageous if you compete in long-distance events such as ultra-marathon or Ironman or if you are prone to GI issues when consuming a high amount of sports nutrition products.

Furthermore, by improving your capacity to use fat as fuel, you enhance your metabolic flexibility, a critical health marker that we will briefly cover in the last section of this article.

A Word Of Caution

While low-carb training brings benefits, you should not do every workout on low glycogen stores. First, you will lose your ability to convert carbohydrates to energy efficiently if you don’t train high-carb from time to time.¹ Second, your exercise capacity is diminished in a low-carb capacity, which may compromise high-intensity training sessions. If you are unable to complete the scheduled training sessions, your long-term training and competition goals may be jeopardized.^1,2 Due to these risks, we recommend you undertake only 30-50% of your training sessions with low-carb availability.²

Metabolic Flexibility

The primary advantage of carb periodization is that it enhances your metabolic flexibility, which is a critical marker of good health.

Metabolic flexibility refers to your body's ability to efficiently use whatever fuel is available, fat or carbs, and seamlessly switch from one fuel source to another. Carb periodization is an excellent way to promote metabolic flexibility since it improves fat oxidation by occasionally exercising with low-carb levels while maintaining carb oxidation efficiency with regular high-carb sessions.

Metabolic flexibility provides many benefits, including sustained energy, fewer blood sugar fluctuations, reduced cravings, and improved fat-burning. As your metabolic flexibility improves, you are less likely to develop conditions like type 2 diabetes and obesity. Individuals suffering from type 2 diabetes or obesity are typically metabolically inflexible, and current research suggests that exercise and carb periodization can help improve metabolic flexibility in skeletal muscle and adipose tissue, which could make them valuable for preventing and treating metabolic diseases.⁷

Conclusion

Hopefully, you have a better understanding of carb periodization and see some potential benefits for you. While we tried to provide enough information to get you started, incorporating carb periodization into your training and nutrition routine might be intimidating. If in doubt, please reach out. We are here to support you. We can work with you to create an individualized nutrition plan and suggest a periodization that best aligns with your training plan, targeted race, and dietary preferences.

As you refine your training diet, it’s important to remember that your recovery is just as important as your training!

In our next article, we will discuss relative energy deficiency in sport (RED-S), its negative consequences on your performance and health, and how adequate nutrition can help mitigate the risks and help you properly recover from training.

References

Burke LM, Hawley JA, Jeukendrup A, Morton JP, Stellingwerff T, Maughan RJ. Toward a Common Understanding of Diet–Exercise Strategies to Manipulate Fuel Availability for Training and Competition Preparation in Endurance Sport. International Journal of Sport Nutrition and Exercise Metabolism. 2018;28(5):451-463.
Impey SG, Hearris MA, Hammond KM, et al. Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Medicine. 2018;48(5):1031-1048.
Jeukendrup AE. Periodized Nutrition for Athletes. Sports medicine (Auckland, NZ). 2017;47(Suppl 1):51-63. doi:10.1007/s40279-017-0694-2
Stellingwerff T, Morton JP, Burke LM. A Framework for Periodized Nutrition for Athletics. Int J Sport Nutr Exerc Metab. 2019;29(2):141-151. doi:10.1123/ijsnem.2018-0305.
Marquet LA, Brisswalter J, Louis J, et al. Enhanced Endurance Performance by Periodization of Carbohydrate Intake: "Sleep Low" Strategy. Med Sci Sports Exerc. 2016;48(4):663-672.
Gejl KD, Nybo L. Performance effects of periodized carbohydrate restriction in endurance trained athletes - a systematic review and meta-analysis. J Int Soc Sports Nutr. 2021;18(1):37.
Goodpaster BH, Sparks LM. Metabolic Flexibility in Health and Disease. Cell Metab. 2017;25(5):1027-1036. doi:10.1016/j.cmet.2017.04.015

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Posted by Gaelle Abecassis