The Ketogenic Diet and Performance: Notes From a Conversation With Dr Fionn McSwiney

Back in May 2020, during the lockdown, I began hosting Instagram Live conversations with various guests to expand my knowledge across different aspects of my practice, including nutrition, sports science, CrossFit, and business. I’m now revisiting and sharing some of these insightful discussions in blog form. One of the highlights was my conversation with Dr. Fionn McSwiney about his research into ketogenic diets (KDs) and performance, his current work at Dublin City University (DCU), and his role as a nutrition consultant at LUCID. Here, I’ll highlight several key takeaways from that conversation.

Low Carb Ketogenic Diet

A significant portion of our discussion revolved around Fionn’s research into ketogenic diets and their impact on performance—a topic that has seen a surge in research interest recently. This uptick is partly due to the growing popularity of KDs and anecdotal reports of their effects on performance, lean muscle mass, and body composition. From a performance perspective, the Low Carb KD (LCKD) has been studied due to the limited energy available from glycogen stores. This is particularly relevant for endurance sports, where glycogen stores provide only about 2000-2200 kcal, which is less than what’s needed for events like marathons. Athletes often consume carbohydrates during races to address this. LCKD might improve fatty acid oxidation during exercise by enhancing mitochondrial density and oxidative enzymes. It could also supply brain fuel via ketone bodies, preserving glucose.

Fionn referenced a notable study by Phinney et al. (1983) which showed that endurance performance at submaximal intensity (62-64% of VO2 max) was maintained on a low-carb diet. There was a research gap until a few years ago when Fionn and others resumed this line of inquiry. His recent paper, “Impact of Ketogenic Diet On Athletes: Current Insights” (2019), reviews existing research on ketogenic diets and performance. The key finding is that LCKD interventions generally do not lead to performance decrements in endurance, maximal strength, or power. The paper is open access, so it’s worth checking out. Our conversation focused more on Fionn’s experiences as a researcher and practitioner rather than just the results of his past research.

Before diving into Fionn’s research, we discussed the importance of education, stepping outside your comfort zone, and embracing the learning process—areas I am keen to improve upon.

Ketogenic Diet and Endurance Performance

We covered Fionn’s first study, which he described as a “considerable undertaking.” It investigated the effect of an LCKD on endurance performance using cyclists performing a 100km time trial on a stationary bike. Key takeaways included no performance decrement with LCKD. However, Fionn openly discussed the study’s limitations. For instance, the carbohydrate group didn’t consume a large amount of carbs before the time trial, which might have been more appropriate. Additionally, the study wasn’t fully randomized; participants chose their groups, leading to a discrepancy in physique between groups. Some low-carb participants had significant body fat to lose, which could confound results related to body composition. The lab-based nature of the study also has limitations, as athletes performed at a set intensity, which may not reflect real-world conditions.

Looking ahead, Fionn highlighted the need for research on health markers and the impact of LCKD on them. Positive health improvements, such as reductions in LDL cholesterol and triglycerides, are likely, particularly in the context of weight loss. However, adherence to an LCKD beyond 12 weeks can lead to increased carbohydrate consumption, potentially resulting in weight gain. Additionally, fiber intake on a KD is a concern since fiber is crucial for cardiovascular health and bowel regularity, and obtaining adequate fiber on a KD can be challenging.

When might a KD be recommended? Fionn suggested it could be suitable for ultra-endurance athletes as part of a periodized approach, where carbs are reintroduced later. It might also be used for elite field athletes needing to lose weight quickly, though with caution. Fionn’s ongoing research shows that a 7-day KD intervention in rowers increased fat oxidation and led to fat loss. However, making such a significant dietary change close to a race should be approached with caution.

Omega Supplements In The Elderly

We briefly touched on Fionn’s current research into multi-ingredient supplements for individuals aged 75 and older. While there were no changes in body composition, significant increases in strength were observed in participants taking whey and omega supplements without a training intervention. This research has promising implications for reducing injuries in older populations.

Finally, Fionn shared insights from his work at his nutrition consultancy, LUCID. His focus on positively impacting individuals, beyond just the science and numbers, resonated with me. This is a value I aim to incorporate into my own practice.

In summary:

- Ketogenic diets generally do not impair performance in endurance, strength, or high-intensity exercises (though they may not offer benefits either).

- Future research should adopt sport-specific approaches, address weight loss confounding factors, and explore health markers and long-term adherence.

- Embrace the learning process, push beyond your expertise, and accept discomfort as part of growth.

- Prioritizing the individual over numbers and science can lead to a greater impact.

- Strive to positively influence others, as Fionn has done with me.

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