Author: Michael Bernstein, MS, IFNCP
Date: April 2025
Please read the article “Energy Systems Used in Endurance and Strength Training” before reading this article, since it contains information that may be helpful in understanding this article.
An important point to make is that the anaerobic and aerobic energy systems both use glycolysis, which specifically uses carbohydrates to produce ATP. Anaerobic glycolysis, which is used to produce energy for physical activities, including long sprints and higher repetition weightlifting, relies on carbohydrates for energy. Aerobic glycolysis, which is used to produce energy for physical activities, including distance running and cycling, also relies on carbohydrates for energy. It is well-established that carbohydrates are necessary for high performance in aerobic exercise such as distance running, however, it is less widely recognized that carbohydrates are needed for activities such as weightlifting. Weightlifting, which involves short, intense bursts of energy, depends heavily on the anaerobic system, which is fueled by carbohydrates. Based on this, low-carb diets may not be ideal for athletes and those engaging in high-intensity exercise. When carbohydrates are consumed, they get broken down into glucose and stored in the muscles and liver as glycogen. During exercise, glycogen is converted back into glucose and used for energy. If early fatigue is experienced during exercise, it may be related to reduced glycogen stores. If a low-carb diet is being followed and early fatigue is experienced during exercise, increasing carbohydrate intake may help alleviate the fatigue. There are other causes of fatigue during exercise, however, a low-carb diet may be a contributing factor. Consuming carbohydrates increases blood sugar which can also can cause increases in insulin. Insulin is an anabolic hormone that facilitates nutrient uptake and tissue growth. It can also help prevent muscle protein breakdown after exercise. As long as total energy and protein intakes are met, carbohydrate consumption can support muscle growth. A study by Henselmans et al. (2022) found that high-carbohydrate intakes may not be necessary for bodybuilders or powerlifters if their workouts included a maximum of 10 sets per muscle group. However, if engaging in 11+ sets per muscle group or another high-intensity workout that same day, increasing carbohydrate consumption may help with glycogen resynthesis. A general recommendation for carbohydrate intake for athletes is 55% or higher of total calories, however, it may vary depending on how much exercise is performed. There are also timing considerations of when to consume carbohydrates, including before, during, and after workouts (Fink & Mikesky, 2021; Lodge et al., 2023).
Another issue with weightlifters has to do with consuming too much protein. 2.2 grams of protein per kilogram of body weight is the maximum amount of protein weightlifters should be consuming to maximize muscle protein synthesis (Stokes et al., 2018). This is a person’s body weight in grams. For a person weighing 150 lbs, this would be 150 grams of protein per day. In a meta-analysis, it was found that a greater intake of protein above 1.6 grams per kilogram of body weight didn’t result in increased muscle hypertrophy (Stokes et al., 2018). The recommended range for protein consumption for athletes is 1.6-2.2 grams per kilogram of body weight (Stokes et al., 2018). In terms of dietary fat consumption, there is the Acceptable Macronutrient Distribution Range (AMDR), which comes from the Dietary Guidelines for Americans. The AMDR for dietary fat is 20-35% of total calories (Harcombe, 2019).
In terms of low-carb diets, they usually consist of high or moderate amounts of protein and fat. Low-carb high-fat (LCHF) diets are popular, as well as the ketogenic diet, which is high fat and extremely low in carbohydrates. A study by Kruszewski et al. (2024), specifically in regards to strength training, found that a low-carb high-fat (LCHF) diet resulted in lower body weight and a reduction in fat mass, while a high-carb low-fat (HCLF) diet resulted in greater muscle mass and increased strength. Those engaging in strength training may want to adjust their macronutrient ratios based on their body composition goals, however, if they are experiencing fatigue and consuming low carbohydrates, they may want to increase their carbohydrate consumption. The ketogenic diet may also offer performance benefits in ultra-endurance events, however, further research is needed. In general, a LCHF diet, as well as the ketogenic diet, may be difficult to sustain long term (Fink & Mikesky, 2021).
References:
Fink, H. H., & Mikesky, A. E. (2021). Practical Applications in Sports Nutrition (6th ed.). Jones & Bartlett Learning.
Henselmans, M., Bjørnsen, T., Hedderman, R., & Vårvik, F. T. (2022). The Effect of Carbohydrate Intake on Strength and Resistance Training Performance: A Systematic Review. Nutrients, 14(4), 856. https://doi.org/10.3390/nu14040856
Lodge, M. T., Ward-Ritacco, C. L., & Melanson, K. J. (2023). Considerations of Low Carbohydrate Availability (LCA) to Relative Energy Deficiency in Sport (RED-S) in Female Endurance Athletes: A Narrative Review. Nutrients, 15(20), 4457. https://doi.org/10.3390/nu15204457
Stokes, T., Hector, A. J., Morton, R. W., McGlory, C., & Phillips, S. M. (2018). Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients, 10(2), 180. https://doi.org/10.3390/nu10020180
Harcombe Z. (2019). US dietary guidelines: is saturated fat a nutrient of concern?. British journal of sports medicine, 53(22), 1393–1396. https://doi.org/10.1136/bjsports-2018-099420
Kruszewski, M., Kruszewski, A., Tabęcki, R., Kuźmicki, S., Stec, K., Ambroży, T., Aksenov, M. O., Merchelski, M., & Danielik, T. (2024). Effectiveness of high-fat and high-carbohydrate diets on body composition and maximal strength after 15 weeks of resistance training. Advances in medical sciences, 69(1), 139–146. https://doi.org/10.1016/j.advms.2024.02.008
* The content provided by this article is for informational purposes only. These statements are not intended to diagnose, treat, cure, or prevent any disease. This article is not intended to provide personal medical advice, which should be obtained from a medical professional.
