Keto diets are everywhere, but how do they stack up for athletes—especially female athletes? With promises of increased fat-burning, metabolic flexibility and improved endurance, keto sounds like a magic bullet. But is it too good to be true? Let’s dive into the latest position stand from the International Society of Sports Nutrition (ISSN). But before we jump in, let’s define what a position stand is and what ketogenic diets entail.

What is a position stand?

A position stand provides a clear, objective summary of the latest evidence on a given topic, in this case, ketogenic diets. To develop this position stand, the ISSN and invited authors completed a critical review of research on ketogenic diets with a focus on athletic performance and body composition (scope n=149 research papers).

What is a ketogenic diet?

The ketogenic diet is high in fat, typically moderate in protein, and extremely low in carbohydrates, though carb cutoffs can vary. The goal is to shift your body into a state of ketosis, where it burns fat for fuel instead of carbohydrates.

This shift to burning fat is viewed as advantageous for athletes given body fat can provide more than 50x more energy than is available in the form of glycogen, or stored carbohydrate¹. With this context, let’s jump into the key conclusions from the ISSN’s review of the evidence on ketogenic diets.

What is the ISSNs Position Stand on Ketogenic Diets?

“1. A ketogenic diet induces a state of nutritional ketosis, which is generally defined as serum ketone levels above 0.5 mM. While factors can impact what amount of daily carbohydrate intake will result in these levels, a broad guideline is a daily dietary carbohydrate intake of less than 50 grams per day.”² (For context, 1 cup of long grain white rice is ~50g of carbs).

“2. Nutritional ketosis achieved through carbohydrate restriction and a high dietary fat intake is not intrinsically harmful and should not be confused with ketoacidosis, a life-threatening condition most commonly seen in clinical populations and metabolic dysregulation.”²

“3. A ketogenic diet has largely neutral or detrimental effects on athletic performance compared to a diet higher in carbohydrates and lower in fat, despite achieving significantly elevated levels of fat oxidation during exercise (~1.5 g/min).”²

“4. The endurance effects of a ketogenic diet may be influenced by both training status and duration of the dietary intervention, but further research is necessary to elucidate these possibilities. All studies involving elite athletes showed a performance decrement from a ketogenic diet, all lasting six weeks or less. Of the two studies lasting more than six weeks, only one reported a statistically significant benefit of a ketogenic diet.”²

“5. A ketogenic diet tends to have similar effects on maximal strength or strength gains from a resistance training program compared to a diet higher in carbohydrates. However, a minority of studies show superior effects of non-ketogenic comparators.”²

“6. When compared to a diet higher in carbohydrates and lower in fat, a ketogenic diet may cause greater losses in body weight, fat mass, and fat-free mass, but may also heighten losses of lean tissue. However, this is likely due to differences in calorie and protein intake, as well as shifts in fluid balance.”²

“7. There is insufficient evidence to determine if a ketogenic diet affects males and females differently. However, there is a strong mechanistic basis for sex differences to exist in response to a ketogenic diet.”²

What are the Sex Differences?

As you may recall from our prior posts, a small fraction of sport & exercise science research (including sports nutrition) is based solely on women, or was intentionally designed to study sex differences in response to a given treatment. Unsurprisingly, this is also the case with respect to the body of research on ketogenic diets.

After a review of the available research, the ISSN noted that males may benefit more from ketogenic diets in terms of increased fat burning and body composition changes which makes sense given well-established sex differences in metabolism as highlighted in the paper i.e. “females metabolize a higher percentage of total energy from fat than males, independent of intensity or mode of exercise, and utilize different proportions of carbohydrate and fat sources for fuel.”²

The Bottom Line: Should You Do Keto?

Before you slash your carb intake, it is important to be aware of the potential risks. The single most important nutritional consideration for health & performance is to ensure you are eating enough for the activity you are doing avoiding chronic low energy availability (LEA) which can lead to a host of serious health & performance issues due to Relative Energy Deficiency in Sport (REDs).³ Research suggests that ~1 in 2 female athletes may be at risk for LEA⁴, and those participating in endurance sports may be at higher risk⁵, which means, you, our gentle reader, may not be eating enough!

Further, new research highlights the importance of also ensuring adequate carbohydrate intake relative as low carbohydrate availability (LCA) may also independently increase the risk of health & performance issues due to REDs, even with adequate energy intake.⁶ Additionally, athletes with LCA may also have deficiencies in important micronutrients.⁶

So instead of cutting carbs, let us help you learn how to fuel for your health & performance! Reach out to schedule a complimentary information call to learn more.

References

1. Jeukendrup, A. & Gleeson, M.. Sport Nutrition 4^th Edition (p. 98). 2024. Human Kinetics.
2. Leaf, A., Rothschild, J. A., Sharpe, T. M., Sims, S. T., Macias, C. J., Futch, G. G., … Antonio, J. (2024). International society of sports nutrition position stand: ketogenic diets. Journal of the International Society of Sports Nutrition, 21(1). https://doi.org/10.1080/15502783.2024.2368167
3. Sims ST, Kerksick CM, Smith-Ryan AE, Janse de Jonge XAK, Hirsch KR, Arent SM, Hewlings SJ, Kleiner SM, Bustillo E, Tartar JL, Starratt VG, Kreider RB, Greenwalt C, Rentería LI, Ormsbee MJ, VanDusseldorp TA, Campbell BI, Kalman DS, Antonio J. International society of sports nutrition position stand: nutritional concerns of the female athlete. J Int Soc Sports Nutr. 2023 Dec;20(1):2204066. doi: 10.1080/15502783.2023.2204066. PMID: 37221858; PMCID: PMC10210857.
4. Holtzman, B., Ackerman, K.E. Recommendations and Nutritional Considerations for Female Athletes: Health and Performance. Sports Med (2021). https://doi.org/10.1007/s40279-021-01508-8
5. Jagim, A. R., Fields, J., Magee, M. K., Kerksick, C. M., & Jones, M. T. (2022). Contributing factors to low energy availability in female athletes: A narrative review of energy availability, training demands, nutrition barriers, body image, and disordered eating. Nutrients, 14(5), 986. https://doi.org/10.3390/nu14050986
6. Birna Vardardottir, Sigridur Lara Gudmundsdottir, Ellen Alma Tryggvadottir, & Olafsdottir, A. S. (2024). Patterns of energy availability and carbohydrate intake differentiate between adaptable and problematic low energy availability in female athletes. Frontiers in Sports and Active Living, 6. https://doi.org/10.3389/fspor.2024.1390558