"Is Butter A Carb?" The Effects of a Ketogenic, Low Carb Diet on Health and Performance
By: Tana Mardian
If you’ve browsed social media or the aisles of a grocery store recently, you have probably heard of the “keto diet.” A ketogenic diet consists of a low carbohydrate, high fat (LCHF) selection of foods that many people have taken interest in due to its alleged association with weight loss. While there are variations of keto, the diet normally calls for about 75-80% of calories coming from foods that are high in fat, such as salmon, avocados, nuts, and seeds. Additionally, carbohydrate consumption should be limited, with the typical ketogenic diet allowing for 50 grams of carbohydrates, which equates to roughly the total amount of carbohydrates in one bagel. With the Dietary Guidelines for Americans calling for 45-65% of energy from carbohydrates (Mayo Clinic, 2022), how does limiting our carb intake affect us, and how might it explicitly affect exercise performance?
Just as a reminder, when we reference carbohydrates (carbs), we’re talking about one of three macronutrients, along with protein and fat. Carbohydrates come in three main forms – sugars, starches, and fibers – and serve as our bodies’ main fuel, especially when it comes to exercise. Our bodies also store carbohydrates in the form of glycogen in the liver and muscles so that we can tap into these stores if we need some more energy; this process is called glycogenolysis (Nakrani et al., 2021). So what happens when we start limiting carbohydrate intake?
To start, a ketogenic diet can cause quick weight loss, more specifically, quick water weight loss. Carol Johnston, a professor and associate director of the nutrition program at Arizona State University, explains this phenomenon. Johnston describes that a few days of low carbohydrate intake will reduce muscular glycogen stores, and for every gram of muscle glycogen that is stored, there are at least 3 grams of water that are stored (ASU College of Health Solutions, Fernández-Elías, et al., 2015). This means that when we deplete glycogen stores, we also lose water, and once someone starts eating carbs again, the weight will quickly return. Johnston also points out that most of us rely on scales, which don’t tell us where the weight loss is coming from, so the keto diet could make someone think they are losing fat (ASU College of Health Solutions).
Since our bodies rely primarily on carbohydrates for exercise, how does a ketogenic diet affect performance? In a study looking into the impact of an LCHF diet on elite race walkers, the investigators observed the detrimental effects of a ketogenic diet on these athletes. The participants on a high carbohydrate diet improved their performance in a 10,000 m race by 4.8%, which equates to about 134 seconds faster compared to the start of the study. On the other hand, those on the LCHF plan experienced significantly slower speeds; their race time worsened by 2.3%, or roughly 86 seconds. Additionally, even though the LCHF group had greater whole-body fat oxidation and increased their aerobic capacity, their walking economy decreased. In other words, the oxygen cost of a given speed increased for this group. This means that, at any given velocity, the LCHF group was doing a greater amount of relative work compared to their high carbohydrate counterparts. We can decipher this by understanding how we get energy from fat compared to carbohydrates. Based on the structure of a fat molecule, more oxygen is required to create the energy currency that our cells use: adenosine triphosphate (ATP). Since these athletes depleted their muscle glycogen and relied on fat at high intensities, their bodies needed more oxygen to make energy. The LCHF athletes were, therefore, less economical; they could get the same amount of energy as the high-carb athletes, but they required much more oxygen to do so. Our bodies will preferentially use carbohydrates for energy, especially at high intensities, due to the fact that we can get more ATP for the same amount of oxygen compared to a fat molecule (Burke et al., 2020).
While decreased athletic performance might not seem like a big deal, the ketogenic diet could potentially have much more serious implications on overall health that outweigh its alleged weight-loss benefits. There are concerns about the high intake of fats in this food plan, which could increase the risk of cardiovascular disease. A high-fat diet may also cause disturbances in the gut microbiome, increasing gut permeability and inflammation. A study looking into the effects of an LCHF diet on normal-weight adults with type 1 diabetes also found evidence of severe health complications, such as dyslipidemia (Valsdottir et al., 2019).
With all of this being said, the social media frenzy around an LCHF diet is a good reminder to read scientifically-backed research before making any big changes in our daily lives. Carbs are certainly not the devil, as many people like to say; they are an essential nutrient for our minds and bodies, meaning that keto might not be all that great. The media is saturated with the hottest and newest “wellness” plans, and as a consequence, we have to dig into the research and talk to physicians before making any decisions. Every person is different, so it’s essential that we pay attention to our internal cues to ensure we are making the best choices for ourselves.
References
Burke, Louise M., Avish P. Sharma, Ida A. Heikura, Sara F. Forbes, Melissa Holloway, Alannah K. A. McKay, Julia L. Bone, Jill J. Leckey, Marijke Welvaert, and Megan L. Ross. “Crisis of Confidence Averted: Impairment of Exercise Economy and Performance in Elite Race Walkers by Ketogenic Low Carbohydrate, High Fat (LCHF) Diet Is Reproducible.” PloS One 15, no. 6 (2020): e0234027. https://doi.org/10.1371/journal.pone.0234027.
Mayo Clinic. “Choose Your Carbs Wisely.” Accessed April 3, 2022. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/carbohydrates/art-20045705.
Fernández-Elías, Valentín E., Juan F. Ortega, Rachael K. Nelson, and Ricardo Mora-Rodriguez. “Relationship between Muscle Water and Glycogen Recovery after Prolonged Exercise in the Heat in Humans.” European Journal of Applied Physiology 115, no. 9 (September 2015): 1919–26. https://doi.org/10.1007/s00421-015-3175-z.
Nakrani, Mihir N., Robert H. Wineland, and Fatima Anjum. “Physiology, Glucose Metabolism.” In StatPearls. Treasure Island (FL): StatPearls Publishing, 2022. http://www.ncbi.nlm.nih.gov/books/NBK560599/.
ASU College of Health Solutions. “The Keto Diet: Is Eating More Fat the Key to Weight Loss?,” August 3, 2017. https://chs.asu.edu/news/keto-diet-eating-more-fat-key-weight-loss.
Valsdottir, Thorhildur Ditta, Christine Henriksen, Nancy Odden, Birgitte Nellemann, Per B. Jeppesen, Jonny Hisdal, Ane C. Westerberg, and Jørgen Jensen. “Effect of a Low-Carbohydrate High-Fat Diet and a Single Bout of Exercise on Glucose Tolerance, Lipid Profile and Endothelial Function in Normal Weight Young Healthy Females.” Frontiers in Physiology 10 (2019). https://www.frontiersin.org/article/10.3389/fphys.2019.01499.